Add an error_handler parameter for UTF-8 to the binary readers and writers

Adds error_handler_t::keep (invalid UTF-8 sequences are left unchanged) as
a fourth error_handler_t value, and threads an error_handler parameter
through the binary writers and readers:

- to_cbor/to_ubjson/to_bjdata/to_bson gain a trailing error_handler
  parameter (default strict, matching their existing type_error.316
  behavior); keep writes a string value or object key's bytes as is
  instead of throwing, and replace/ignore sanitize it exactly like
  dump() would, including for the BSON length prefix. to_msgpack and
  to_bon8 are unchanged.
- from_cbor/from_msgpack/from_ubjson/from_bjdata/from_bson gain a
  trailing error_handler parameter (default keep, i.e. the lenient
  behavior every binary reader had in 3.12.0 and still has after
  #5741); strict checks every string value and object key and raises
  parse_error.113 for ill-formed UTF-8, honoring allow_exceptions;
  replace/ignore sanitize it like dump() would. from_bon8 is
  unchanged, since UTF-8 lead bytes are structural there.

dump()'s own keep support writes ill-formed bytes as is, even with
ensure_ascii, while still \u-escaping well-formed characters around
them as usual.

The UTF-8 validity check (is_valid_utf8) and the replace/ignore
sanitizing logic (sanitize_utf8) now live in string_utils.hpp, shared
by the serializer and the binary reader/writer; error_handler_t itself
moved to its own header (detail/output/error_handler.hpp) so that
string_utils.hpp does not need to depend on serializer.hpp.

See #5529 and #5741.

Signed-off-by: Niels Lohmann <mail@nlohmann.me>

.github/workflows/check_amalgamation.yml

@@ -2,23 +2,16 @@ name: "Check amalgamation"
 
 on:
   pull_request:
-  # also check develop itself: a PR can be merged before its own run of this
-  # workflow completes (e.g. while it is still queued), leaving single_include
-  # stale on develop without any failing check
-  push:
-    branches:
-      - develop
 
 concurrency:
   group: ${{ github.workflow }}-${{ github.ref || github.run_id }}
-  cancel-in-progress: ${{ github.event_name == 'pull_request' }}
+  cancel-in-progress: true
 
 permissions:
   contents: read
 
 jobs:
   save:
-    if: github.event_name == 'pull_request'
     runs-on: ubuntu-latest
     steps:
       - name: Harden Runner
@@ -50,11 +43,11 @@ jobs:
         with:
           egress-policy: audit
 
-      - name: Checkout pull request or pushed commit
+      - name: Checkout pull request
         uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7.0.1
         with:
           path: main
-          ref: ${{ github.event.pull_request.head.sha || github.sha }}
+          ref: ${{ github.event.pull_request.head.sha }}
           persist-credentials: false
 
       - name: Checkout tools

.github/workflows/comment_check_amalgamation.yml

@@ -10,8 +10,7 @@ permissions:
 
 jobs:
   comment:
-    # push runs on develop have no PR to comment on (and no "pr" artifact)
-    if: ${{ github.event.workflow_run.conclusion == 'failure' && github.event.workflow_run.event == 'pull_request' }}
+    if: ${{ github.event.workflow_run.conclusion == 'failure' }}
     runs-on: ubuntu-latest
     permissions:
       contents: read

README.md

@@ -1394,7 +1394,7 @@ THE SOFTWARE IS PROVIDED “AS IS”, WITHOUT WARRANTY OF ANY KIND, EXPRESS OR I
 - The class contains a slightly modified version of the Grisu2 algorithm from Florian Loitsch which is licensed under the [MIT License](https://opensource.org/licenses/MIT) (see above). Copyright © 2009 [Florian Loitsch](https://florian.loitsch.com/)
 - The class contains a copy of [Hedley](https://nemequ.github.io/hedley/) from Evan Nemerson which is licensed as [CC0-1.0](https://creativecommons.org/publicdomain/zero/1.0/).
 - The class contains parts of [Google Abseil](https://github.com/abseil/abseil-cpp) which is licensed under the [Apache 2.0 License](https://opensource.org/licenses/Apache-2.0).
-- The class contains an adapted version of the Eisel-Lemire algorithm, its table of powers of five, and its digit comparison for long numbers from [fast_float](https://github.com/fastfloat/fast_float) by Daniel Lemire and contributors, which is available under the [MIT License](https://opensource.org/licenses/MIT) (used here), the Apache 2.0 License, and the Boost Software License. Copyright © 2021 The fast_float authors
+- The class contains an adapted version of the Eisel-Lemire algorithm and its table of powers of five from [fast_float](https://github.com/fastfloat/fast_float) by Daniel Lemire and contributors, which is available under the [MIT License](https://opensource.org/licenses/MIT) (used here), the Apache 2.0 License, and the Boost Software License. Copyright © 2021 The fast_float authors
 
 <img align="right" src="https://git.fsfe.org/reuse/reuse-ci/raw/branch/master/reuse-horizontal.png" alt="REUSE Software">
 

docs/mkdocs/docs/api/basic_json/dump.md

@@ -25,10 +25,12 @@ and `ensure_ascii` parameters.
     result consists of ASCII characters only.
 
 `error_handler` (in)
-:   how to react on decoding errors; there are three possible values (see [`error_handler_t`](error_handler_t.md):
+:   how to react on decoding errors; there are four possible values (see [`error_handler_t`](error_handler_t.md):
     `strict` (throws an exception in case a decoding error occurs; default), `replace` (replace invalid UTF-8 sequences
-    with U+FFFD), and `ignore` (ignore invalid UTF-8 sequences during serialization; all valid bytes are copied to the
-    output unchanged, and invalid bytes are dropped)).
+    with U+FFFD), `ignore` (ignore invalid UTF-8 sequences during serialization; all valid bytes are copied to the
+    output unchanged, and invalid bytes are dropped), and `keep` (write the ill-formed bytes to the output as is,
+    without escaping them, even if `ensure_ascii` is `#!cpp true`; the result is then not valid UTF-8, but equals the
+    input bytes exactly, and well-formed characters around the ill-formed bytes are still escaped as usual)).
     
 ## Return value
 
@@ -94,3 +96,4 @@ Binary values are serialized as an object containing two keys:
 - Indentation character `indent_char`, option `ensure_ascii` and exceptions added in version 3.0.0.
 - Error handlers added in version 3.4.0.
 - Serialization of binary values added in version 3.8.0.
+- Error handler `keep` added in version 3.13.0.

docs/mkdocs/docs/api/basic_json/error_handler_t.md

@@ -4,15 +4,30 @@
 enum class error_handler_t {
     strict,
     replace,
-    ignore
+    ignore,
+    keep
 };
 ```
 
-This enumeration is used in the [`dump`](dump.md) function to choose how to treat decoding errors while serializing a
-`basic_json` value. Three values are differentiated:
+This enumeration is used to choose how to treat ill-formed UTF-8 in a string value or object key:
+
+- [`dump`](dump.md) uses it while serializing a `basic_json` value to text.
+- [`to_cbor`](to_cbor.md), [`to_ubjson`](to_ubjson.md), [`to_bjdata`](to_bjdata.md), and [`to_bson`](to_bson.md) use it
+  while serializing a `basic_json` value to that binary format; none of CBOR, UBJSON, BJData, or BSON requires a
+  decoder to reject ill-formed UTF-8, so by default (`strict`) the library checks on write instead. `to_msgpack` and
+  `to_bon8` do not take this parameter: MessagePack's specification explicitly allows a string to contain ill-formed
+  UTF-8, so `to_msgpack` always passes it through, while BON8 always validates, since UTF-8 lead bytes are structural
+  to that format.
+- [`from_cbor`](from_cbor.md), [`from_msgpack`](from_msgpack.md), [`from_ubjson`](from_ubjson.md),
+  [`from_bjdata`](from_bjdata.md), and [`from_bson`](from_bson.md) use it while parsing that binary format, to decide
+  whether to check a string value or object key for well-formed UTF-8 at all; by default (`keep`) they do not, as no
+  binary reader did before this parameter was added. `from_bon8` does not take this parameter, for the same reason
+  `to_bon8` does not.
+
+Four values are differentiated:
 
 strict
-:   throw a `type_error` exception in case of invalid UTF-8
+:   throw a `type_error`/`parse_error` exception in case of invalid UTF-8
 
 replace
 :   replace invalid UTF-8 sequences with U+FFFD (� REPLACEMENT CHARACTER)
@@ -20,6 +35,12 @@ replace
 ignore
 :   ignore invalid UTF-8 sequences; all valid bytes are copied to the output unchanged, and invalid bytes are dropped
 
+keep
+:   keep invalid UTF-8 sequences unchanged; only meaningful for the binary formats mentioned above, since [`dump`]
+    (dump.md) itself must produce text, and `keep` there writes the ill-formed bytes to the output as is, so the
+    result is then not valid UTF-8 (but still equals the input bytes exactly, including around any well-formed
+    characters, which are still escaped as usual)
+
 ## Examples
 
 ??? example
@@ -40,3 +61,5 @@ ignore
 ## Version history
 
 - Added in version 3.4.0.
+- Added `keep`, and made this enumeration apply to the binary readers and writers in addition to `dump`, in version
+  3.13.0.

docs/mkdocs/docs/api/basic_json/from_bjdata.md

@@ -5,12 +5,14 @@
 template<typename InputType>
 static basic_json from_bjdata(InputType&& i,
                               const bool strict = true,
-                              const bool allow_exceptions = true);
+                              const bool allow_exceptions = true,
+                              const error_handler_t error_handler = error_handler_t::keep);
 // (2)
 template<typename IteratorType, typename SentinelType = IteratorType>
 static basic_json from_bjdata(IteratorType first, SentinelType last,
                               const bool strict = true,
-                              const bool allow_exceptions = true);
+                              const bool allow_exceptions = true,
+                              const error_handler_t error_handler = error_handler_t::keep);
 ```
 
 Deserializes a given input to a JSON value using the BJData (Binary JData) serialization format.
@@ -58,6 +60,12 @@ The exact mapping and its limitations are described on a [dedicated page](../../
 `allow_exceptions` (in)
 :   whether to throw exceptions in case of a parse error (optional, `#!cpp true` by default)
 
+`error_handler` (in)
+:   how to treat a string value or object key that is not valid UTF-8; see [`error_handler_t`](error_handler_t.md).
+    BJData does not require a decoder to reject ill-formed UTF-8, so checking is opt-in: the default, `keep`, does not
+    check at all, as every binary reader did before this parameter was added; `strict` checks and throws;
+    `replace`/`ignore` sanitize the string the same way [`dump`](dump.md) would
+
 ## Return value
 
 deserialized JSON value; in case of a parse error and `allow_exceptions` set to `#!cpp false`, the return value will be
@@ -73,7 +81,7 @@ Strong guarantee: if an exception is thrown, there are no changes in the JSON va
   the end of the file was not reached when `strict` was set to true
 - Throws [parse_error.112](../../home/exceptions.md#jsonexceptionparse_error112) if a parse error occurs
 - Throws [parse_error.113](../../home/exceptions.md#jsonexceptionparse_error113) if a string could not be parsed
-  successfully
+  successfully, or if a string value or object key is not valid UTF-8 and `error_handler` is `strict`
 - Throws [out_of_range.408](../../home/exceptions.md#jsonexceptionout_of_range408) if the size of an optimized container
   or n-dimensional array cannot be represented by `std::size_t`
 
@@ -111,3 +119,4 @@ Linear in the size of the input.
 - Added in version 3.11.0.
 - Extended container support (1) to include types with lvalue-only ADL `begin`/`end` (matching `std::begin`/`std::end` semantics) in version 3.13.0.
 - Extended overload (2) to accept heterogeneous iterator+sentinel pairs (C++20 ranges support) in version 3.13.0.
+- Added `error_handler` parameter in version 3.13.0.

docs/mkdocs/docs/api/basic_json/from_bson.md

@@ -5,12 +5,14 @@
 template<typename InputType>
 static basic_json from_bson(InputType&& i,
                             const bool strict = true,
-                            const bool allow_exceptions = true);
+                            const bool allow_exceptions = true,
+                            const error_handler_t error_handler = error_handler_t::keep);
 // (2)
 template<typename IteratorType, typename SentinelType = IteratorType>
 static basic_json from_bson(IteratorType first, SentinelType last,
                             const bool strict = true,
-                            const bool allow_exceptions = true);
+                            const bool allow_exceptions = true,
+                            const error_handler_t error_handler = error_handler_t::keep);
 ```
 
 Deserializes a given input to a JSON value using the BSON (Binary JSON) serialization format.
@@ -58,6 +60,12 @@ The exact mapping and its limitations are described on a [dedicated page](../../
 `allow_exceptions` (in)
 :   whether to throw exceptions in case of a parse error (optional, `#!cpp true` by default)
 
+`error_handler` (in)
+:   how to treat a string value or object key that is not valid UTF-8; see [`error_handler_t`](error_handler_t.md).
+    BSON does not require a decoder to reject ill-formed UTF-8, so checking is opt-in: the default, `keep`, does not
+    check at all, as every binary reader did before this parameter was added; `strict` checks and throws;
+    `replace`/`ignore` sanitize the string the same way [`dump`](dump.md) would
+
 ## Return value
 
 deserialized JSON value; in case of a parse error and `allow_exceptions` set to `#!cpp false`, the return value will be
@@ -75,6 +83,8 @@ Strong guarantee: if an exception is thrown, there are no changes in the JSON va
   invalid string or byte array length)
 - Throws [`parse_error.114`](../../home/exceptions.md#jsonexceptionparse_error114) if an unsupported BSON record type is
   encountered
+- Throws [`parse_error.113`](../../home/exceptions.md#jsonexceptionparse_error113) if a string value or object key is
+  not valid UTF-8 and `error_handler` is `strict`
 
 ## Complexity
 
@@ -111,6 +121,7 @@ Linear in the size of the input.
 - Added in version 3.4.0.
 - Extended container support (1) to include types with lvalue-only ADL `begin`/`end` (matching `std::begin`/`std::end` semantics) in version 3.13.0.
 - Extended overload (2) to accept heterogeneous iterator+sentinel pairs (C++20 ranges support) in version 3.13.0.
+- Added `error_handler` parameter in version 3.13.0.
 
 !!! warning "Deprecation"
 

docs/mkdocs/docs/api/basic_json/from_cbor.md

@@ -6,14 +6,16 @@ template<typename InputType>
 static basic_json from_cbor(InputType&& i,
                             const bool strict = true,
                             const bool allow_exceptions = true,
-                            const cbor_tag_handler_t tag_handler = cbor_tag_handler_t::error);
+                            const cbor_tag_handler_t tag_handler = cbor_tag_handler_t::error,
+                            const error_handler_t error_handler = error_handler_t::keep);
 
 // (2)
 template<typename IteratorType, typename SentinelType = IteratorType>
 static basic_json from_cbor(IteratorType first, SentinelType last,
                             const bool strict = true,
                             const bool allow_exceptions = true,
-                            const cbor_tag_handler_t tag_handler = cbor_tag_handler_t::error);
+                            const cbor_tag_handler_t tag_handler = cbor_tag_handler_t::error,
+                            const error_handler_t error_handler = error_handler_t::keep);
 ```
 
 Deserializes a given input to a JSON value using the CBOR (Concise Binary Object Representation) serialization format.
@@ -65,6 +67,12 @@ The exact mapping and its limitations are described on a [dedicated page](../../
 :   how to treat CBOR tags (optional, `error` by default); see [`cbor_tag_handler_t`](cbor_tag_handler_t.md) for more
     information
 
+`error_handler` (in)
+:   how to treat a string value or object key that is not valid UTF-8; see [`error_handler_t`](error_handler_t.md).
+    CBOR does not require a decoder to reject ill-formed UTF-8, so checking is opt-in: the default, `keep`, does not
+    check at all, as every binary reader did before this parameter was added; `strict` checks and throws;
+    `replace`/`ignore` sanitize the string the same way [`dump`](dump.md) would
+
 ## Return value
 
 deserialized JSON value; in case of a parse error and `allow_exceptions` set to `#!cpp false`, the return value will be
@@ -80,8 +88,9 @@ Strong guarantee: if an exception is thrown, there are no changes in the JSON va
   the end of the file was not reached when `strict` was set to true
 - Throws [parse_error.112](../../home/exceptions.md#jsonexceptionparse_error112) if unsupported features from CBOR were
   used in the given input or if the input is not valid CBOR
-- Throws [parse_error.113](../../home/exceptions.md#jsonexceptionparse_error113) if a map key is not a string (keys of other
-  types are not supported, as JSON object keys are always strings) or a string is malformed
+- Throws [parse_error.113](../../home/exceptions.md#jsonexceptionparse_error113) if a map key is not a string (keys of
+  other types are not supported, as JSON object keys are always strings), or if a string value or object key is not
+  valid UTF-8 and `error_handler` is `strict`
 
 ## Complexity
 
@@ -121,6 +130,7 @@ Linear in the size of the input.
 - Added `tag_handler` parameter in version 3.9.0.
 - Extended container support (1) to include types with lvalue-only ADL `begin`/`end` (matching `std::begin`/`std::end` semantics) in version 3.13.0.
 - Extended overload (2) to accept heterogeneous iterator+sentinel pairs (C++20 ranges support) in version 3.13.0.
+- Added `error_handler` parameter in version 3.13.0.
 
 !!! warning "Deprecation"
 

docs/mkdocs/docs/api/basic_json/from_msgpack.md

@@ -5,12 +5,14 @@
 template<typename InputType>
 static basic_json from_msgpack(InputType&& i,
                                const bool strict = true,
-                               const bool allow_exceptions = true);
+                               const bool allow_exceptions = true,
+                               const error_handler_t error_handler = error_handler_t::keep);
 // (2)
 template<typename IteratorType, typename SentinelType = IteratorType>
 static basic_json from_msgpack(IteratorType first, SentinelType last,
                                const bool strict = true,
-                               const bool allow_exceptions = true);
+                               const bool allow_exceptions = true,
+                               const error_handler_t error_handler = error_handler_t::keep);
 ```
 
 Deserializes a given input to a JSON value using the MessagePack serialization format.
@@ -58,6 +60,12 @@ The exact mapping and its limitations are described on a [dedicated page](../../
 `allow_exceptions` (in)
 :   whether to throw exceptions in case of a parse error (optional, `#!cpp true` by default)
 
+`error_handler` (in)
+:   how to treat a string value or object key that is not valid UTF-8; see [`error_handler_t`](error_handler_t.md).
+    MessagePack's specification explicitly allows ill-formed UTF-8, so checking is opt-in: the default, `keep`, does
+    not check at all, as every binary reader did before this parameter was added; `strict` checks and throws;
+    `replace`/`ignore` sanitize the string the same way [`dump`](dump.md) would
+
 ## Return value
 
 deserialized JSON value; in case of a parse error and `allow_exceptions` set to `#!cpp false`, the return value will be
@@ -73,8 +81,9 @@ Strong guarantee: if an exception is thrown, there are no changes in the JSON va
   the end of the file was not reached when `strict` was set to true
 - Throws [parse_error.112](../../home/exceptions.md#jsonexceptionparse_error112) if unsupported features from
   MessagePack were used in the given input or if the input is not valid MessagePack
-- Throws [parse_error.113](../../home/exceptions.md#jsonexceptionparse_error113) if a map key is not a string (keys of other
-  types are not supported, as JSON object keys are always strings) or a string is malformed
+- Throws [parse_error.113](../../home/exceptions.md#jsonexceptionparse_error113) if a map key is not a string (keys of
+  other types are not supported, as JSON object keys are always strings), or if a string value or object key is not
+  valid UTF-8 and `error_handler` is `strict`
 
 ## Complexity
 
@@ -113,6 +122,7 @@ Linear in the size of the input.
 - Added `allow_exceptions` parameter in version 3.2.0.
 - Extended container support (1) to include types with lvalue-only ADL `begin`/`end` (matching `std::begin`/`std::end` semantics) in version 3.13.0.
 - Extended overload (2) to accept heterogeneous iterator+sentinel pairs (C++20 ranges support) in version 3.13.0.
+- Added `error_handler` parameter in version 3.13.0.
 
 !!! warning "Deprecation"
 

docs/mkdocs/docs/api/basic_json/from_ubjson.md

@@ -5,12 +5,14 @@
 template<typename InputType>
 static basic_json from_ubjson(InputType&& i,
                               const bool strict = true,
-                              const bool allow_exceptions = true);
+                              const bool allow_exceptions = true,
+                              const error_handler_t error_handler = error_handler_t::keep);
 // (2)
 template<typename IteratorType, typename SentinelType = IteratorType>
 static basic_json from_ubjson(IteratorType first, SentinelType last,
                               const bool strict = true,
-                              const bool allow_exceptions = true);
+                              const bool allow_exceptions = true,
+                              const error_handler_t error_handler = error_handler_t::keep);
 ```
 
 Deserializes a given input to a JSON value using the UBJSON (Universal Binary JSON) serialization format.
@@ -58,6 +60,12 @@ The exact mapping and its limitations are described on a [dedicated page](../../
 `allow_exceptions` (in)
 :   whether to throw exceptions in case of a parse error (optional, `#!cpp true` by default)
 
+`error_handler` (in)
+:   how to treat a string value or object key that is not valid UTF-8; see [`error_handler_t`](error_handler_t.md).
+    UBJSON does not require a decoder to reject ill-formed UTF-8, so checking is opt-in: the default, `keep`, does not
+    check at all, as every binary reader did before this parameter was added; `strict` checks and throws;
+    `replace`/`ignore` sanitize the string the same way [`dump`](dump.md) would
+
 ## Return value
 
 deserialized JSON value; in case of a parse error and `allow_exceptions` set to `#!cpp false`, the return value will be
@@ -73,7 +81,7 @@ Strong guarantee: if an exception is thrown, there are no changes in the JSON va
   the end of the file was not reached when `strict` was set to true
 - Throws [parse_error.112](../../home/exceptions.md#jsonexceptionparse_error112) if a parse error occurs
 - Throws [parse_error.113](../../home/exceptions.md#jsonexceptionparse_error113) if a string could not be parsed
-  successfully
+  successfully, or if a string value or object key is not valid UTF-8 and `error_handler` is `strict`
 - Throws [out_of_range.408](../../home/exceptions.md#jsonexceptionout_of_range408) if the size of an optimized container
   or n-dimensional array cannot be represented by `std::size_t`
 
@@ -112,6 +120,7 @@ Linear in the size of the input.
 - Added `allow_exceptions` parameter in version 3.2.0.
 - Extended container support (1) to include types with lvalue-only ADL `begin`/`end` (matching `std::begin`/`std::end` semantics) in version 3.13.0.
 - Extended overload (2) to accept heterogeneous iterator+sentinel pairs (C++20 ranges support) in version 3.13.0.
+- Added `error_handler` parameter in version 3.13.0.
 
 !!! warning "Deprecation"
 

docs/mkdocs/docs/api/basic_json/number_float_t.md

@@ -23,10 +23,9 @@ type to use.
 ## Template parameters
 
 `NumberFloatType`
-:   the type to store floating-point numbers. The parser converts `#!cpp float`, `#!cpp double`, and a
-    `#!cpp long double` that is IEEE 754 binary64 itself and other `#!cpp long double` formats with
-    `#!cpp std::from_chars` or `#!cpp std::strtold`, and serialization falls back to `#!cpp std::snprintf`, so the
-    type must be `#!cpp float`, `#!cpp double`, or `#!cpp long double`. The
+:   the type to store floating-point numbers. Parsing and serialization are implemented in terms of
+    `#!cpp std::strtof`/`#!cpp std::strtod`/`#!cpp std::strtold` and `#!cpp std::snprintf`, so the type must be
+    `#!cpp float`, `#!cpp double`, or `#!cpp long double`. The
     [binary formats](../../features/binary_formats/index.md) additionally require `#!cpp float` or `#!cpp double`,
     because they have no encoding for `#!cpp long double`. See
     [Template Parameter Requirements](../../features/types/template_parameters.md#numberfloattype).

docs/mkdocs/docs/api/basic_json/to_bjdata.md

@@ -5,15 +5,18 @@
 static std::vector<std::uint8_t> to_bjdata(const basic_json& j,
                                            const bool use_size = false,
                                            const bool use_type = false,
-                                           const bjdata_version_t version = bjdata_version_t::draft2);
+                                           const bjdata_version_t version = bjdata_version_t::draft2,
+                                           const error_handler_t error_handler = error_handler_t::strict);
 
 // (2)
 static void to_bjdata(const basic_json& j, detail::output_adapter<std::uint8_t> o,
                       const bool use_size = false, const bool use_type = false,
-                      const bjdata_version_t version = bjdata_version_t::draft2);
+                      const bjdata_version_t version = bjdata_version_t::draft2,
+                      const error_handler_t error_handler = error_handler_t::strict);
 static void to_bjdata(const basic_json& j, detail::output_adapter<char> o,
                       const bool use_size = false, const bool use_type = false,
-                      const bjdata_version_t version = bjdata_version_t::draft2);
+                      const bjdata_version_t version = bjdata_version_t::draft2,
+                      const error_handler_t error_handler = error_handler_t::strict);
 ```
 
 Serializes a given JSON value `j` to a byte vector using the BJData (Binary JData) serialization format. BJData aims to
@@ -43,6 +46,12 @@ The exact mapping and its limitations are described on a [dedicated page](../../
 :   which version of BJData to use (see note on "Binary values" on [BJData](../../features/binary_formats/bjdata.md));
 optional, `#!cpp bjdata_version_t::draft2` by default.
 
+`error_handler` (in)
+:   how to treat a string or object key in `j` that is not valid UTF-8; see [`error_handler_t`](error_handler_t.md).
+    The default, `strict`, throws; `keep` writes the ill-formed bytes to the output as is, as every version of
+    `to_bjdata` did before this parameter was added; `replace`/`ignore` sanitize it the same way
+    [`dump`](dump.md) would
+
 ## Return value
 
 1. BJData serialization as byte vector
@@ -56,6 +65,8 @@ Strong guarantee: if an exception is thrown, there are no changes in the JSON va
 
 - Throws [`other_error.502`](../../home/exceptions.md#jsonexceptionother_error502) if `use_type` is true and `use_size`
   is false.
+- Throws [type_error.316](../../home/exceptions.md#jsonexceptiontype_error316) if a string or object key in `j` is
+  not valid UTF-8 and `error_handler` is `strict` (the default)
 
 ## Complexity
 
@@ -89,4 +100,6 @@ Linear in the size of the JSON value `j`.
 ## Version history
 
 - Added in version 3.11.0.
-- BJData version parameter (for draft3 binary encoding) added in version 3.12.0.
+- BJData version parameter (for draft3 binary encoding) added in version 3.12.0.
+- Throwing `type_error.316` for a string or object key that is not valid UTF-8 added in version 3.13.0.
+- Added `error_handler` parameter in version 3.13.0.

docs/mkdocs/docs/api/basic_json/to_bson.md

@@ -2,11 +2,14 @@
 
 ```cpp
 // (1)
-static std::vector<std::uint8_t> to_bson(const basic_json& j);
+static std::vector<std::uint8_t> to_bson(const basic_json& j,
+                                         const error_handler_t error_handler = error_handler_t::strict);
 
 // (2)
-static void to_bson(const basic_json& j, detail::output_adapter<std::uint8_t> o);
-static void to_bson(const basic_json& j, detail::output_adapter<char> o);
+static void to_bson(const basic_json& j, detail::output_adapter<std::uint8_t> o,
+                    const error_handler_t error_handler = error_handler_t::strict);
+static void to_bson(const basic_json& j, detail::output_adapter<char> o,
+                    const error_handler_t error_handler = error_handler_t::strict);
 ```
 
 BSON (Binary JSON) is a binary format in which zero or more ordered key/value pairs are stored as a single entity (a
@@ -25,6 +28,12 @@ The exact mapping and its limitations are described on a [dedicated page](../../
 `o` (in)
 :   output adapter to write serialization to
 
+`error_handler` (in)
+:   how to treat a string or object key in `j` that is not valid UTF-8; see [`error_handler_t`](error_handler_t.md).
+    The default, `strict`, throws; `keep` writes the ill-formed bytes to the output as is, as every version of
+    `to_bson` did before this parameter was added; `replace`/`ignore` sanitize it the same way
+    [`dump`](dump.md) would
+
 ## Return value
 
 1. BSON serialization as a byte vector
@@ -46,6 +55,8 @@ Strong guarantee: if an exception is thrown, there are no changes in the JSON va
 - Throws [`out_of_range.415`](../../home/exceptions.md#jsonexceptionout_of_range415) if the subtype of a binary value
   exceeds 255, the maximum of the BSON binary subtype; example:
   `"subtype 70000 is too large for the BSON binary subtype (max 255)"`
+- Throws [type_error.316](../../home/exceptions.md#jsonexceptiontype_error316) if a string or object key is
+  not valid UTF-8 and `error_handler` is `strict` (the default)
 
 ## Complexity
 
@@ -82,3 +93,6 @@ pass before anything is written.
 - Added in version 3.4.0.
 - Linear in the size of `j`, and no longer limited by the call stack for deeply nested values, since version 3.13.0.
 - `out_of_range.415` is now detected before anything is written, like the other exceptions above, since version 3.13.0.
+- Throwing `type_error.316` for a string value or object key that is not valid UTF-8, detected before anything is
+  written, added in version 3.13.0.
+- Added `error_handler` parameter in version 3.13.0.

docs/mkdocs/docs/api/basic_json/to_cbor.md

@@ -2,11 +2,14 @@
 
 ```cpp
 // (1)
-static std::vector<std::uint8_t> to_cbor(const basic_json& j);
+static std::vector<std::uint8_t> to_cbor(const basic_json& j,
+                                          const error_handler_t error_handler = error_handler_t::strict);
 
 // (2)
-static void to_cbor(const basic_json& j, detail::output_adapter<std::uint8_t> o);
-static void to_cbor(const basic_json& j, detail::output_adapter<char> o);
+static void to_cbor(const basic_json& j, detail::output_adapter<std::uint8_t> o,
+                     const error_handler_t error_handler = error_handler_t::strict);
+static void to_cbor(const basic_json& j, detail::output_adapter<char> o,
+                     const error_handler_t error_handler = error_handler_t::strict);
 ```
 
 Serializes a given JSON value `j` to a byte vector using the CBOR (Concise Binary Object Representation) serialization
@@ -26,6 +29,12 @@ The exact mapping and its limitations are described on a [dedicated page](../../
 `o` (in)
 :   output adapter to write serialization to
 
+`error_handler` (in)
+:   how to treat a string or object key in `j` that is not valid UTF-8; see [`error_handler_t`](error_handler_t.md).
+    The default, `strict`, throws; `keep` writes the ill-formed bytes to the output as is, as every version of
+    `to_cbor` did before this parameter was added; `replace`/`ignore` sanitize it the same way
+    [`dump`](dump.md) would
+
 ## Return value
 
 1. CBOR serialization as a byte vector
@@ -35,6 +44,11 @@ The exact mapping and its limitations are described on a [dedicated page](../../
 
 Strong guarantee: if an exception is thrown, there are no changes in the JSON value.
 
+## Exceptions
+
+- Throws [type_error.316](../../home/exceptions.md#jsonexceptiontype_error316) if a string or object key in `j` is
+  not valid UTF-8 and `error_handler` is `strict` (the default)
+
 ## Complexity
 
 Linear in the size of the JSON value `j`.
@@ -68,3 +82,5 @@ Linear in the size of the JSON value `j`.
 
 - Added in version 2.0.9.
 - Compact representation of floating-point numbers added in version 3.8.0.
+- Throwing `type_error.316` for a string or object key that is not valid UTF-8 added in version 3.13.0.
+- Added `error_handler` parameter in version 3.13.0.

docs/mkdocs/docs/api/basic_json/to_ubjson.md

@@ -4,13 +4,16 @@
 // (1)
 static std::vector<std::uint8_t> to_ubjson(const basic_json& j,
                                            const bool use_size = false,
-                                           const bool use_type = false);
+                                           const bool use_type = false,
+                                           const error_handler_t error_handler = error_handler_t::strict);
 
 // (2)
 static void to_ubjson(const basic_json& j, detail::output_adapter<std::uint8_t> o,
-                      const bool use_size = false, const bool use_type = false);
+                      const bool use_size = false, const bool use_type = false,
+                      const error_handler_t error_handler = error_handler_t::strict);
 static void to_ubjson(const basic_json& j, detail::output_adapter<char> o,
-                      const bool use_size = false, const bool use_type = false);
+                      const bool use_size = false, const bool use_type = false,
+                      const error_handler_t error_handler = error_handler_t::strict);
 ```
 
 Serializes a given JSON value `j` to a byte vector using the UBJSON (Universal Binary JSON) serialization format. UBJSON
@@ -36,6 +39,12 @@ The exact mapping and its limitations are described on a [dedicated page](../../
 :   whether to add type annotations to container types (must be combined with `#!cpp use_size = true`); optional,
     `#!cpp false` by default.
 
+`error_handler` (in)
+:   how to treat a string or object key in `j` that is not valid UTF-8; see [`error_handler_t`](error_handler_t.md).
+    The default, `strict`, throws; `keep` writes the ill-formed bytes to the output as is, as every version of
+    `to_ubjson` did before this parameter was added; `replace`/`ignore` sanitize it the same way
+    [`dump`](dump.md) would
+
 ## Return value
 
 1. UBJSON serialization as a byte vector
@@ -49,6 +58,8 @@ Strong guarantee: if an exception is thrown, there are no changes in the JSON va
 
 - Throws [`other_error.502`](../../home/exceptions.md#jsonexceptionother_error502) if `use_type` is true and `use_size`
   is false.
+- Throws [type_error.316](../../home/exceptions.md#jsonexceptiontype_error316) if a string or object key in `j` is
+  not valid UTF-8 and `error_handler` is `strict` (the default)
 
 ## Complexity
 
@@ -82,3 +93,5 @@ Linear in the size of the JSON value `j`.
 ## Version history
 
 - Added in version 3.1.0.
+- Throwing `type_error.316` for a string or object key that is not valid UTF-8 added in version 3.13.0.
+- Added `error_handler` parameter in version 3.13.0.

docs/mkdocs/docs/examples/error_handler_t.cpp

@@ -20,5 +20,6 @@ int main()
               << j_invalid.dump(-1, ' ', false, json::error_handler_t::replace)
               << "\nstring with ignored invalid characters: "
               << j_invalid.dump(-1, ' ', false, json::error_handler_t::ignore)
-              << '\n';
+              << "\nstring with the invalid byte kept as is (" << j_invalid.dump(-1, ' ', false, json::error_handler_t::keep).size()
+              << " bytes, not valid UTF-8 itself)\n";
 }

docs/mkdocs/docs/examples/error_handler_t.output

@@ -1,3 +1,4 @@
 [json.exception.type_error.316] invalid UTF-8 byte at index 2: 0xA9
 string with replaced invalid characters: "ä�ü"
 string with ignored invalid characters: "äü"
+string with the invalid byte kept as is (7 bytes, not valid UTF-8 itself)

docs/mkdocs/docs/features/binary_formats/bjdata.md

@@ -63,6 +63,12 @@ The library uses the following mapping from JSON values types to BJData types ac
 
       - strings with more than 18446744073709551615 bytes, i.e., 2<sup>64</sup>-1 bytes (theoretical)
 
+!!! warning "UTF-8 validation of string values and object keys"
+
+    BJData strings must use UTF-8 encoding. `to_bjdata()` validates the bytes of every string value and object key
+    and throws [`type_error.316`](../../home/exceptions.md#jsonexceptiontype_error316) for ill-formed UTF-8, so a
+    value with such a string cannot be serialized in the first place.
+
 !!! info "Unused BJData markers"
 
     The following markers are not used in the conversion:
@@ -208,6 +214,20 @@ The library maps BJData types to JSON value types as follows:
 
     The mapping is **complete** in the sense that any BJData value can be converted to a JSON value.
 
+!!! warning "Ill-formed UTF-8 in string values and object keys"
+
+    BJData strings must use UTF-8 encoding, but checking it on read is opt-in: with the
+    [`error_handler`](../../api/basic_json/from_bjdata.md) parameter left at `keep` (the default), `from_bjdata()`
+    accepts a string value or object key whose bytes are not valid UTF-8 and hands them back unchanged. Passing
+    `error_handler_t::strict` makes `from_bjdata()` check and throw
+    [`parse_error.113`](../../home/exceptions.md#jsonexceptionparse_error113) for ill-formed UTF-8, and
+    `replace`/`ignore` sanitize the string instead of keeping it. However,
+    [`dump()`](../../api/basic_json/dump.md) still requires valid UTF-8 and throws
+    [`type_error.316`](../../home/exceptions.md#jsonexceptiontype_error316) for a value read with the default
+    `keep` handler, unless an error handler is passed that replaces or ignores the ill-formed bytes. `to_bjdata()`'s
+    own `error_handler` parameter defaults to `strict` (see above), so a value read this way cannot be written back
+    to BJData unless a non-strict handler is passed there too.
+
 !!! info "Round trips"
 
     A value returned by [`from_bjdata`](../../api/basic_json/from_bjdata.md) can be serialized with

docs/mkdocs/docs/features/binary_formats/bson.md

@@ -109,14 +109,22 @@ The library maps BSON record types to JSON value types as follows:
     If BSON input must be validated for strict specification compliance, validate it separately before passing it to
     `from_bson()`.
 
-!!! warning "UTF-8 validation of string values"
+!!! warning "Ill-formed UTF-8 in string values"
 
-    The BSON specification requires `string` values (type `0x02`) to be valid UTF-8. This library validates the
-    bytes of every such string at decode time and rejects ill-formed UTF-8 with a
-    [`parse_error.113`](../../home/exceptions.md#jsonexceptionparse_error113) exception (or, with `allow_exceptions`
-    set to `false`, a discarded value), rather than only failing later when the resulting value is dumped. Element
-    (key) names and `binary` values (type `0x05`) are unaffected and are never validated, since they are read
-    byte-by-byte as a C string, or are not required to hold text, respectively.
+    The BSON specification requires `string` values (type `0x02`) to be valid UTF-8, but this is not required of a
+    decoder, so checking is opt-in: with the [`error_handler`](../../api/basic_json/from_bson.md) parameter left at
+    `keep` (the default), `from_bson()` accepts a `string` value whose bytes are not valid UTF-8 and hands them back
+    unchanged. Passing `error_handler_t::strict` makes `from_bson()` check and throw
+    [`parse_error.113`](../../home/exceptions.md#jsonexceptionparse_error113) for ill-formed UTF-8, and
+    `replace`/`ignore` sanitize the string instead of keeping it. However, [`dump()`](../../api/basic_json/dump.md)
+    still requires valid UTF-8 and throws [`type_error.316`](../../home/exceptions.md#jsonexceptiontype_error316)
+    for a value read with the default `keep` handler, unless an error handler is passed that replaces or ignores
+    the ill-formed bytes. `to_bson()`'s own `error_handler` parameter defaults to `strict` and throws the same
+    exception for a string value or element (key) name that is not valid UTF-8, so an object with such a key or
+    value cannot be produced in the first place unless a non-strict handler is passed there, even though
+    `from_bson()` would accept it from another source with the default `keep` handler. Element (key) names are
+    never validated on read, since they are read byte-by-byte as a C string. `binary` values (type `0x05`) are
+    unaffected, since they are not required to hold text.
 
 ??? example
 

docs/mkdocs/docs/features/binary_formats/cbor.md

@@ -189,15 +189,21 @@ The library maps CBOR types to JSON value types as follows:
     ([RFC 8392](https://www.rfc-editor.org/rfc/rfc8392.html)), cannot be read with this library and need a
     general-purpose CBOR library instead.
 
-!!! warning "UTF-8 validation of text strings"
+!!! warning "Ill-formed UTF-8 in text strings"
 
     [RFC 8949, Section 3.1](https://www.rfc-editor.org/rfc/rfc8949.html#section-3.1) requires CBOR text strings
-    (major type 3) to be valid UTF-8. This library validates the bytes of every text string (object keys included) at
-    decode time and rejects ill-formed UTF-8 with a
-    [`parse_error.113`](../../home/exceptions.md#jsonexceptionparse_error113) exception (or, with
-    `allow_exceptions` set to `false`, a discarded value), rather than only failing later when the resulting value is
-    dumped. Byte strings (major type 2) are unaffected and are never validated, since they are not required to hold
-    text.
+    (major type 3) to be valid UTF-8, but leaves it up to the decoder whether to enforce this, so checking is
+    opt-in: with the [`error_handler`](../../api/basic_json/from_cbor.md) parameter left at `keep` (the default),
+    `from_cbor()` accepts a text string (object keys included) whose bytes are not valid UTF-8 and hands them back
+    unchanged. Passing `error_handler_t::strict` makes `from_cbor()` check and throw
+    [`parse_error.113`](../../home/exceptions.md#jsonexceptionparse_error113) for ill-formed UTF-8, and
+    `replace`/`ignore` sanitize the string instead of keeping it. However, [`dump()`](../../api/basic_json/dump.md)
+    still requires valid UTF-8 and throws [`type_error.316`](../../home/exceptions.md#jsonexceptiontype_error316)
+    for a value read with the default `keep` handler, unless an error handler is passed that replaces or ignores
+    the ill-formed bytes. `to_cbor()`'s own [`error_handler`](../../api/basic_json/to_cbor.md) parameter defaults
+    to `strict` and throws the same exception for a string value or object key that is not valid UTF-8, so such a
+    value cannot be written back to CBOR unless a non-strict handler is passed there too. Byte strings (major
+    type 2) are unaffected, since they are not required to hold text.
 
 !!! warning "Tagged items"
 

docs/mkdocs/docs/features/binary_formats/messagepack.md

@@ -153,14 +153,21 @@ The library maps MessagePack types to JSON value types as follows:
     This applies to the [SAX interface](../parsing/sax_interface.md) as well, as the key is read before it is passed
     on. Such input needs a general-purpose MessagePack library instead.
 
-!!! warning "UTF-8 validation of string values"
+!!! warning "Ill-formed UTF-8 in string values"
 
-    The MessagePack specification requires `str` values (`fixstr`, `str 8`, `str 16`, `str 32`) to be valid UTF-8.
-    This library validates the bytes of every such string (object keys included) at decode time and rejects
-    ill-formed UTF-8 with a [`parse_error.113`](../../home/exceptions.md#jsonexceptionparse_error113) exception (or,
-    with `allow_exceptions` set to `false`, a discarded value), rather than only failing later when the resulting
-    value is dumped. `bin`/`ext`/`fixext` values are unaffected and are never validated, since they are not required
-    to hold text.
+    The MessagePack specification explicitly allows a `str` value (`fixstr`, `str 8`, `str 16`, `str 32`) to contain
+    a byte sequence that is not valid UTF-8, and expects a deserializer to hand the original bytes back unchanged.
+    This library follows that by default: with its
+    [`error_handler`](../../api/basic_json/from_msgpack.md) parameter left at `keep` (the default),
+    `from_msgpack()` reads `str` bytes (object keys included) as-is, without validating them, so such a value
+    round-trips through `from_msgpack(to_msgpack(j))` byte for byte. Passing `error_handler_t::strict` makes
+    `from_msgpack()` check anyway and throw
+    [`parse_error.113`](../../home/exceptions.md#jsonexceptionparse_error113) for ill-formed UTF-8, and
+    `replace`/`ignore` sanitize the string instead of keeping it. `to_msgpack()` itself has no `error_handler`
+    parameter and always writes `str` bytes as-is, since the specification permits it. However,
+    [`dump()`](../../api/basic_json/dump.md) still requires valid UTF-8 and throws
+    [`type_error.316`](../../home/exceptions.md#jsonexceptiontype_error316) for a value read this way with the
+    default `keep` handler, unless an error handler is passed that replaces or ignores the ill-formed bytes.
 
 ??? example
 

docs/mkdocs/docs/features/binary_formats/ubjson.md

@@ -47,6 +47,12 @@ The library uses the following mapping from JSON values types to UBJSON types ac
 
       - strings with more than 9223372036854775807 bytes (theoretical)
 
+!!! warning "UTF-8 validation of string values and object keys"
+
+    UBJSON's required string encoding is UTF-8. `to_ubjson()` validates the bytes of every string value and object
+    key and throws [`type_error.316`](../../home/exceptions.md#jsonexceptiontype_error316) for ill-formed UTF-8, so
+    a value with such a string cannot be serialized in the first place.
+
 !!! info "Unused UBJSON markers"
 
     The following markers are not used in the conversion:
@@ -120,6 +126,20 @@ The library maps UBJSON types to JSON value types as follows:
 
     The mapping is **complete** in the sense that any UBJSON value can be converted to a JSON value.
 
+!!! warning "Ill-formed UTF-8 in string values and object keys"
+
+    UBJSON's required string encoding is UTF-8, but checking it on read is opt-in: with the
+    [`error_handler`](../../api/basic_json/from_ubjson.md) parameter left at `keep` (the default), `from_ubjson()`
+    accepts a string value or object key whose bytes are not valid UTF-8 and hands them back unchanged. Passing
+    `error_handler_t::strict` makes `from_ubjson()` check and throw
+    [`parse_error.113`](../../home/exceptions.md#jsonexceptionparse_error113) for ill-formed UTF-8, and
+    `replace`/`ignore` sanitize the string instead of keeping it. However,
+    [`dump()`](../../api/basic_json/dump.md) still requires valid UTF-8 and throws
+    [`type_error.316`](../../home/exceptions.md#jsonexceptiontype_error316) for a value read with the default
+    `keep` handler, unless an error handler is passed that replaces or ignores the ill-formed bytes. `to_ubjson()`'s
+    own `error_handler` parameter defaults to `strict` (see above), so a value read this way cannot be written back
+    to UBJSON unless a non-strict handler is passed there too.
+
 ??? example
 
     ```cpp

docs/mkdocs/docs/features/types/number_handling.md

@@ -71,13 +71,10 @@ otherwise, it uses unsigned integer storage.
 
     - Numbers with a decimal digit or scientific notation are always stored as `#!c double`.
     - The number types can be changed, see [Template number types](#template-number-types). 
-    - The library converts integers and floating-point numbers itself, independent of the locale. Floating-point
-      numbers are correctly rounded (to nearest, ties to even). Only a `#!c long double` that is not IEEE 754 binary64
-      (e.g., the 80-bit x87 format) is converted with `#!cpp std::from_chars` where available, or else with
-      [`std::strtold`](https://en.cppreference.com/w/cpp/string/byte/strtof). For that call, the library temporarily
-      replaces the `.` with the decimal point of the current locale (which may be longer than one byte, e.g., in
-      `fa_IR.UTF-8`), so the result does not depend on the locale either. Changing the locale in another thread during
-      parsing is undefined behavior of the C library, though.
+    - As of version 3.9.1, the conversion is realized by
+      [`std::strtoull`](https://en.cppreference.com/w/cpp/string/byte/strtoul),
+      [`std::strtoll`](https://en.cppreference.com/w/cpp/string/byte/strtol), and
+      [`std::strtod`](https://en.cppreference.com/w/cpp/string/byte/strtof), respectively.
 
 !!! example "Examples"
 
@@ -88,10 +85,10 @@ otherwise, it uses unsigned integer storage.
 ### Number limits
 
 - Any 64-bit signed or unsigned integer can be stored without loss of precision.
-- Numbers exceeding the limits of `#!c double` (i.e., numbers whose rounded value is not satisfying
+- Numbers exceeding the limits of `#!c double` (i.e., numbers that after conversion via
+[`std::strtod`](https://en.cppreference.com/w/cpp/string/byte/strtof) are not satisfying
 [`std::isfinite`](https://en.cppreference.com/w/cpp/numeric/math/isfinite) such as `#!c 1E400`) will throw exception
-[`json.exception.out_of_range.406`](../../home/exceptions.md#jsonexceptionout_of_range406) during parsing. Numbers too
-small for `#!c double` (such as `#!c 1E-400`) become zero, with the sign of the number.
+[`json.exception.out_of_range.406`](../../home/exceptions.md#jsonexceptionout_of_range406) during parsing.
 - Floating-point numbers are rounded to the next number representable as `double`. For instance
 `#!c 3.141592653589793238462643383279` is stored as [`0x400921fb54442d18`](https://float.exposed/0x400921fb54442d18).
 This is the same behavior as the code `#!c double x = 3.141592653589793238462643383279;`.

docs/mkdocs/docs/features/types/template_parameters.md

@@ -26,9 +26,8 @@ Requirements are split into two groups:
     diagnosed with dedicated error messages, and violating most of them results in a compiler error somewhere inside
     the library. Four violations are not caught at compile time at all:
 
-    - A [`StringType`](#stringtype) whose `data()` is not null-terminated compiles and silently misparses numbers
-      stored as a `#!cpp long double` that is not IEEE 754 binary64 (e.g., the 80-bit x87 format), because the lexer
-      hands the buffer to `#!cpp std::strtold`.
+    - A [`StringType`](#stringtype) whose `data()` is not null-terminated compiles and silently misparses numbers,
+      because the lexer hands the buffer to `#!cpp std::strtoull`/`#!cpp std::strtoll`/`#!cpp std::strtod`.
     - A stateful [`AllocatorType`](#allocatortype) compiles and silently ignores its state: allocation, deallocation,
       and [`get_allocator()`](../../api/basic_json/get_allocator.md) each use a different default-constructed instance.
     - The two [cross-specialization conversions](#cross-specialization-conversions) below. These abort on an assertion
@@ -536,10 +535,8 @@ therefore silently changes parse results rather than raising an error. See
 
 `NumberFloatType` must be one of `#!cpp float`, `#!cpp double`, or `#!cpp long double`:
 
-- The [parser](../parsing/index.md) converts number literals to `#!cpp float`, `#!cpp double`, and a
-  `#!cpp long double` that is IEEE 754 binary64 itself; other `#!cpp long double` formats are converted with
-  `#!cpp std::from_chars` where available, or with `#!cpp std::strtold`. The library provides overloads for exactly
-  these three types.
+- The [parser](../parsing/index.md) converts number literals with `#!cpp std::strtof`, `#!cpp std::strtod`, or
+  `#!cpp std::strtold`; the library provides overloads for exactly these three types.
 - [`dump`](../../api/basic_json/dump.md) falls back to `#!cpp std::snprintf` with the `%g` and `%Lg` conversion
   specifiers, for which the library likewise provides only `#!cpp double` and `#!cpp long double` overloads
   (`#!cpp float` is promoted to `#!cpp double`).

docs/mkdocs/docs/home/exceptions.md

@@ -341,7 +341,10 @@ An unexpected byte was read in a [binary format](../features/binary_formats/inde
 
 A string could not be read from a [binary format](../features/binary_formats/index.md): either a value that is not a
 string was read where one was required (for instance as a map key), the string's length specification is invalid, or
-the string's bytes are not valid UTF-8.
+the string's bytes are not valid UTF-8 and the `error_handler` parameter of the corresponding `from_*` function is
+set to `strict`. By default (`error_handler_t::keep`), the bytes of a string are not checked for valid UTF-8 on read;
+see the ill-formed UTF-8 notes on the individual [binary format](../features/binary_formats/index.md) pages for how
+such a string is handled depending on `error_handler`.
 
 CBOR and MessagePack allow map keys of any type, but JSON object keys are always strings. Maps with keys of any other
 type (for instance integers or `null`) are therefore not supported; see the notes on

docs/mkdocs/docs/home/license.md

@@ -20,4 +20,4 @@ The class contains a slightly modified version of the Grisu2 algorithm from Flor
 
 The class contains a copy of [Hedley](https://nemequ.github.io/hedley/) from Evan Nemerson which is licensed as [CC0-1.0](https://creativecommons.org/publicdomain/zero/1.0/).
 
-The class contains an adapted version of the Eisel-Lemire algorithm, its table of powers of five, and its digit comparison for long numbers from [fast_float](https://github.com/fastfloat/fast_float) by Daniel Lemire and contributors, which is available under the [MIT License](https://opensource.org/licenses/MIT) (used here), the Apache 2.0 License, and the Boost Software License. Copyright © 2021 The fast_float authors
+The class contains an adapted version of the Eisel-Lemire algorithm and its table of powers of five from [fast_float](https://github.com/fastfloat/fast_float) by Daniel Lemire and contributors, which is available under the [MIT License](https://opensource.org/licenses/MIT) (used here), the Apache 2.0 License, and the Boost Software License. Copyright © 2021 The fast_float authors

include/nlohmann/detail/input/binary_reader.hpp

@@ -31,6 +31,7 @@
 #include <nlohmann/detail/macro_scope.hpp>
 #include <nlohmann/detail/meta/is_sax.hpp>
 #include <nlohmann/detail/meta/type_traits.hpp>
+#include <nlohmann/detail/output/error_handler.hpp>
 #include <nlohmann/detail/string_concat.hpp>
 #include <nlohmann/detail/string_utils.hpp>
 #include <nlohmann/detail/value_t.hpp>
@@ -108,8 +109,16 @@ class binary_reader
     @brief create a binary reader
 
     @param[in] adapter  input adapter to read from
+    @param[in] format   the binary format to parse
+    @param[in] error_handler  how to treat text strings and object keys that
+               are not well-formed UTF-8; none of the supported formats
+               requires a decoder to reject those, so the default is to
+               @ref error_handler_t::keep them unchanged, as every binary
+               reader did before this parameter existed
     */
-    explicit binary_reader(InputAdapterType&& adapter, const input_format_t format = input_format_t::json) noexcept : ia(std::move(adapter)), input_format(format)
+    explicit binary_reader(InputAdapterType&& adapter, const input_format_t format = input_format_t::json,
+                           const error_handler_t error_handler = error_handler_t::keep) noexcept
+        : ia(std::move(adapter)), input_format(format), error_handler(error_handler)
     {
         (void)detail::is_sax_static_asserts<SAX, BasicJsonType> {};
     }
@@ -428,7 +437,7 @@ class binary_reader
     {
         if (get_bson_cstr_bulk(result, std::integral_constant<bool, bulk_scan> {}))
         {
-            return true;
+            return check_string_utf8(result, "key");
         }
 
         auto out = std::back_inserter(result);
@@ -441,7 +450,7 @@ class binary_reader
             }
             if (current == 0x00)
             {
-                return true;
+                return check_string_utf8(result, "key");
             }
             *out++ = static_cast<typename string_t::value_type>(current);
         }
@@ -522,7 +531,7 @@ class binary_reader
                                             "string"), nullptr));
         }
 
-        return true;
+        return check_string_utf8(result, "string");
     }
 
     /*!
@@ -1149,7 +1158,7 @@ class binary_reader
 
     @return whether string creation completed
     */
-    bool get_cbor_string(string_t& result)
+    bool get_cbor_string(string_t& result, const char* context = "string")
     {
         // number of indefinite-length strings that have been opened and not
         // closed yet. RFC 8949, Section 3.2.3 does not permit nesting them,
@@ -1179,7 +1188,7 @@ class binary_reader
             {
                 if (--open == 0)
                 {
-                    return true;
+                    return check_string_utf8(result, context);
                 }
                 get();
                 continue;
@@ -1192,7 +1201,7 @@ class binary_reader
 
             if (open == 0)
             {
-                return true;
+                return check_string_utf8(result, context);
             }
 
             get();
@@ -1216,7 +1225,7 @@ class binary_reader
         // EOF and major type 3 (text string) are left to get_cbor_string
         if (current == char_traits<char_type>::eof() || (static_cast<unsigned int>(current) & 0xE0u) == 0x60u)
         {
-            return get_cbor_string(result);
+            return get_cbor_string(result, "key");
         }
 
         const char* found = nullptr;
@@ -2004,7 +2013,7 @@ class binary_reader
 
     @return whether string creation completed
     */
-    bool get_msgpack_string(string_t& result)
+    bool get_msgpack_string(string_t& result, const char* context = "string")
     {
         if (JSON_HEDLEY_UNLIKELY(!unexpect_eof(input_format_t::msgpack, "string")))
         {
@@ -2047,25 +2056,25 @@ class binary_reader
             case 0xBE:
             case 0xBF:
             {
-                return get_string(input_format_t::msgpack, static_cast<unsigned int>(current) & 0x1Fu, result);
+                return get_string(input_format_t::msgpack, static_cast<unsigned int>(current) & 0x1Fu, result) && check_string_utf8(result, context);
             }
 
             case 0xD9: // str 8
             {
                 std::uint8_t len{};
-                return get_number(input_format_t::msgpack, len) && get_string(input_format_t::msgpack, len, result);
+                return get_number(input_format_t::msgpack, len) && get_string(input_format_t::msgpack, len, result) && check_string_utf8(result, context);
             }
 
             case 0xDA: // str 16
             {
                 std::uint16_t len{};
-                return get_number(input_format_t::msgpack, len) && get_string(input_format_t::msgpack, len, result);
+                return get_number(input_format_t::msgpack, len) && get_string(input_format_t::msgpack, len, result) && check_string_utf8(result, context);
             }
 
             case 0xDB: // str 32
             {
                 std::uint32_t len{};
-                return get_number(input_format_t::msgpack, len) && get_string(input_format_t::msgpack, len, result);
+                return get_number(input_format_t::msgpack, len) && get_string(input_format_t::msgpack, len, result) && check_string_utf8(result, context);
             }
 
             default:
@@ -2143,7 +2152,7 @@ class binary_reader
                 // byte 0xC1 are left to get_msgpack_string
                 if (current == char_traits<char_type>::eof())
                 {
-                    return get_msgpack_string(result);
+                    return get_msgpack_string(result, "key");
                 }
                 if (current <= 0x7F || current >= 0xE0)
                 {
@@ -2159,7 +2168,7 @@ class binary_reader
                 }
                 else
                 {
-                    return get_msgpack_string(result);
+                    return get_msgpack_string(result, "key");
                 }
                 break;
         }
@@ -2405,7 +2414,7 @@ class binary_reader
                         if (top.is_object)
                         {
                             key.clear();
-                            if (JSON_HEDLEY_UNLIKELY(!get_ubjson_string(key) || !sax->key(key)))
+                            if (JSON_HEDLEY_UNLIKELY(!get_ubjson_string(key, true, "key") || !sax->key(key)))
                             {
                                 return false;
                             }
@@ -2427,7 +2436,7 @@ class binary_reader
                     if (top.is_object)
                     {
                         key.clear();
-                        if (JSON_HEDLEY_UNLIKELY(!get_ubjson_string(key, false) || !sax->key(key)))
+                        if (JSON_HEDLEY_UNLIKELY(!get_ubjson_string(key, false, "key") || !sax->key(key)))
                         {
                             return false;
                         }
@@ -2495,7 +2504,7 @@ class binary_reader
 
     @return whether string creation completed
     */
-    bool get_ubjson_string(string_t& result, const bool get_char = true)
+    bool get_ubjson_string(string_t& result, const bool get_char = true, const char* context = "string")
     {
         if (get_char)
         {
@@ -2516,31 +2525,31 @@ class binary_reader
             case 'U':
             {
                 std::uint8_t len{};
-                return get_number(input_format, len) && get_string(input_format, len, result);
+                return get_number(input_format, len) && get_string(input_format, len, result) && check_string_utf8(result, context);
             }
 
             case 'i':
             {
                 std::int8_t len{};
-                return get_number(input_format, len) && check_ubjson_string_length(len) && get_string(input_format, len, result);
+                return get_number(input_format, len) && check_ubjson_string_length(len) && get_string(input_format, len, result) && check_string_utf8(result, context);
             }
 
             case 'I':
             {
                 std::int16_t len{};
-                return get_number(input_format, len) && check_ubjson_string_length(len) && get_string(input_format, len, result);
+                return get_number(input_format, len) && check_ubjson_string_length(len) && get_string(input_format, len, result) && check_string_utf8(result, context);
             }
 
             case 'l':
             {
                 std::int32_t len{};
-                return get_number(input_format, len) && check_ubjson_string_length(len) && get_string(input_format, len, result);
+                return get_number(input_format, len) && check_ubjson_string_length(len) && get_string(input_format, len, result) && check_string_utf8(result, context);
             }
 
             case 'L':
             {
                 std::int64_t len{};
-                return get_number(input_format, len) && check_ubjson_string_length(len) && get_string(input_format, len, result);
+                return get_number(input_format, len) && check_ubjson_string_length(len) && get_string(input_format, len, result) && check_string_utf8(result, context);
             }
 
             case 'u':
@@ -2550,7 +2559,7 @@ class binary_reader
                     break;
                 }
                 std::uint16_t len{};
-                return get_number(input_format, len) && get_string(input_format, len, result);
+                return get_number(input_format, len) && get_string(input_format, len, result) && check_string_utf8(result, context);
             }
 
             case 'm':
@@ -2560,7 +2569,7 @@ class binary_reader
                     break;
                 }
                 std::uint32_t len{};
-                return get_number(input_format, len) && get_string(input_format, len, result);
+                return get_number(input_format, len) && get_string(input_format, len, result) && check_string_utf8(result, context);
             }
 
             case 'M':
@@ -2570,7 +2579,7 @@ class binary_reader
                     break;
                 }
                 std::uint64_t len{};
-                return get_number(input_format, len) && get_string(input_format, len, result);
+                return get_number(input_format, len) && get_string(input_format, len, result) && check_string_utf8(result, context);
             }
 
             default:
@@ -4031,27 +4040,50 @@ class binary_reader
                     const NumberType len,
                     string_t& result)
     {
-        // get_bytes() appends to result, and CBOR indefinite-length strings
-        // collect all their chunks in the same result; validating only the
-        // newly read bytes keeps the check linear in the input size
-        const std::size_t old_size = result.size();
-        if (JSON_HEDLEY_UNLIKELY(!get_bytes(format, len, "string", result)))
+        // Strings are taken as is by default: none of CBOR (RFC 8949 §3.1
+        // leaves the choice to the decoder), MessagePack (whose spec
+        // explicitly allows a str object to contain an invalid byte
+        // sequence), UBJSON, BJData, or BSON requires a decoder to reject
+        // ill-formed UTF-8. Checking (and, with @ref error_handler_t::strict,
+        // rejecting, or with `replace`/`ignore`, sanitizing) is opt-in via
+        // @ref error_handler, applied once the whole string (all chunks of
+        // an indefinite-length CBOR string included) has been assembled, by
+        // @ref check_string_utf8 at the call site.
+        return get_bytes(format, len, "string", result);
+    }
+
+    /*!
+    @brief validate a decoded text string (value or object key) against @ref error_handler
+
+    None of the binary formats requires a decoder to reject ill-formed UTF-8
+    in a text string (see @ref get_string), so by default
+    (@ref error_handler_t::keep) this does nothing. A stricter
+    @ref error_handler opts into the same well-formedness check @ref
+    serializer::dump_escaped_impl applies when dumping a string:
+    @ref error_handler_t::strict rejects ill-formed input with
+    parse_error.113 (honoring `allow_exceptions` via @a sax), while
+    @ref error_handler_t::replace / @ref error_handler_t::ignore sanitize
+    @a result in place, using the exact same rules.
+
+    @param[in,out] result  the already assembled string to check
+    @param[in] context     further context information (for diagnostics)
+    @return whether @a result is acceptable (always true for `keep`)
+    */
+    bool check_string_utf8(string_t& result, const char* context)
+    {
+        if (error_handler == error_handler_t::keep || is_valid_utf8(result))
         {
-            return false;
+            return true;
         }
 
-        // RFC 8949 (CBOR) §3.1 and the MessagePack/BSON/UBJSON specifications
-        // all require text strings to be valid UTF-8; reject anything else
-        // right here so malformed input is caught at decode time instead of
-        // only surfacing later as a type_error.316 when the value is dumped
-        // (which would defeat allow_exceptions=false / strict discarding).
-        if (JSON_HEDLEY_UNLIKELY(!is_valid_utf8(result, old_size)))
+        if (error_handler == error_handler_t::strict)
         {
-            return sax->parse_error(chars_read, get_token_string(),
-                                    parse_error::create(113, chars_read,
-                                            exception_message(format, "invalid string: ill-formed UTF-8 byte", "string"), nullptr));
+            auto last_token = get_token_string();
+            return sax->parse_error(chars_read, last_token, parse_error::create(113, chars_read,
+                                    exception_message(input_format, "invalid string: ill-formed UTF-8 byte", context), nullptr));
         }
 
+        result = sanitize_utf8(result, error_handler);
         return true;
     }
 
@@ -4226,6 +4258,9 @@ class binary_reader
     /// input format
     const input_format_t input_format = input_format_t::json;
 
+    /// how to treat text strings/object keys that are not well-formed UTF-8
+    const error_handler_t error_handler = error_handler_t::keep;
+
     /// the SAX parser
     json_sax_t* sax = nullptr;
 

include/nlohmann/detail/input/lexer.hpp

@@ -1039,11 +1039,9 @@ class lexer : public lexer_base<BasicJsonType>
             token_type::parse_error otherwise
 
     @note The scanner is independent of the current locale: token_buffer
-          always holds `.`. The conversion of float and double does not use
-          the locale either. Only the std::strtold fallback of
-          convert_number() for long double formats other than binary64
-          depends on it, and it looks up the decimal point right before
-          converting (see detail::convert_float_locale_aware()).
+          always holds `.`. Only the std::strtod fallback of convert_number()
+          depends on the locale, and it looks up the decimal point right
+          before converting (see detail::convert_float_locale_aware()).
     */
     token_type scan_number()  // lgtm [cpp/use-of-goto] `goto` is used in this function to implement the number-parsing state machine described above. By design, any finite input will eventually reach the "done" state or return token_type::parse_error. In each intermediate state, 1 byte of the input is appended to the token_buffer vector, and only the already initialized variables token_buffer, number_type, and error_message are manipulated.
     {
@@ -1056,7 +1054,7 @@ class lexer : public lexer_base<BasicJsonType>
 
         // offset just past the last mantissa byte in token_buffer (i.e. the
         // index of 'e'/'E', or the whole token when there is no exponent).
-        // convert_number() uses it to split the token; npos means
+        // convert_number() uses it to count significant digits; npos means
         // "not seen an exponent yet" and is resolved at scan_number_done
         std::size_t mantissa_end = std::string::npos;
 
@@ -1386,8 +1384,8 @@ scan_number_done:
     @param[in] mantissa_end  offset just past the last mantissa byte in
                              token_buffer (the index of 'e'/'E', or
                              token_buffer.size() when there is no exponent);
-                             with decimal_point_position, it locates the parts
-                             of a float token without scanning it again
+                             used to skip Clinger's fast path when it cannot
+                             possibly succeed - see detail::mantissa_fits_clinger()
     */
     token_type convert_number(token_type number_type, std::size_t mantissa_end)
     {
@@ -1441,11 +1439,10 @@ scan_number_done:
         }
 
         // this code is reached if we parse a floating-point number or if an
-        // integer conversion above overflowed. float and double (and long
-        // double where it is binary64) are converted by the library itself,
-        // correctly rounded and independent of the locale; other long double
-        // formats use std::from_chars when available, otherwise the
-        // locale-aware strtold.
+        // integer conversion above overflowed. Prefer std::from_chars
+        // (Eisel-Lemire, locale-independent, correctly rounded) when available;
+        // otherwise the exact Clinger fast path (double only); otherwise the
+        // locale-aware strtof/strtod/strtold.
         if (convert_float_fast(num_begin, num_end, decimal_point_position, mantissa_end, value_float))
         {
             return token_type::value_float;

include/nlohmann/detail/output/binary_writer.hpp

@@ -26,6 +26,7 @@
 #include <nlohmann/detail/input/binary_reader.hpp>
 #include <nlohmann/detail/input/string_scan.hpp>
 #include <nlohmann/detail/macro_scope.hpp>
+#include <nlohmann/detail/output/error_handler.hpp>
 #include <nlohmann/detail/output/output_adapters.hpp>
 #include <nlohmann/detail/string_concat.hpp>
 #include <nlohmann/detail/string_utils.hpp>
@@ -93,8 +94,12 @@ class binary_writer
     @param[in] sink  output sink to write to (a value-type sink such as
                      output_vector_sink, or output_adapter_sink wrapping a
                      type-erased output adapter)
+    @param[in] error_handler_  how to treat a string value or object key that
+               is not valid UTF-8 (CBOR, UBJSON, BJData, and BSON only; never
+               consulted by @ref write_msgpack or @ref write_bon8)
     */
-    explicit binary_writer(OutputSinkType sink) : oa(std::move(sink))
+    explicit binary_writer(OutputSinkType sink, const error_handler_t error_handler_ = error_handler_t::strict)
+        : oa(std::move(sink)), error_handler(error_handler_)
     {}
 
     /*!
@@ -107,14 +112,20 @@ class binary_writer
     from one.
 
     @param[in] adapter  output adapter to write to
+    @param[in] error_handler_  how to treat a string value or object key that
+               is not valid UTF-8 (CBOR, UBJSON, BJData, and BSON only; never
+               consulted by @ref write_msgpack or @ref write_bon8)
     */
     template < typename SinkType = OutputSinkType,
                typename std::enable_if < std::is_constructible<SinkType, output_adapter_t<CharType>>::value, int >::type = 0 >
-    explicit binary_writer(output_adapter_t<CharType> adapter) : oa(SinkType(std::move(adapter)))
+    explicit binary_writer(output_adapter_t<CharType> adapter, const error_handler_t error_handler_ = error_handler_t::strict)
+        : oa(SinkType(std::move(adapter))), error_handler(error_handler_)
     {}
 
     /*!
     @param[in] j  JSON value to serialize
+    @throw type_error.316 if a string value or an object key is not valid
+           UTF-8
     @throw type_error.317 if @a j is not an object
     */
     void write_bson(const BasicJsonType& j)
@@ -145,6 +156,8 @@ class binary_writer
 
     /*!
     @param[in] j  JSON value to serialize
+    @throw type_error.316 if a string value or an object key is not valid
+           UTF-8
     */
     void write_cbor(const BasicJsonType& j)
     {
@@ -211,13 +224,16 @@ class binary_writer
 
             case value_t::string:
             {
+                string_t storage;
+                const string_t& value = sanitize_utf8_for_write(*j.m_data.m_value.string, j, storage);
+
                 // step 1: write control byte and the string length
-                write_cbor_head(0x60, j.m_data.m_value.string->size());
+                write_cbor_head(0x60, value.size());
 
                 // step 2: write the string
                 oa.write_characters(
-                      reinterpret_cast<const CharType*>(j.m_data.m_value.string->data()),
-                      j.m_data.m_value.string->size());
+                      reinterpret_cast<const CharType*>(value.data()),
+                      value.size());
                 break;
             }
 
@@ -287,6 +303,17 @@ class binary_writer
                 // step 2: write each element
                 for (const auto& el : *j.m_data.m_value.object)
                 {
+                    // el.first is checked here, against the object as
+                    // diagnostics context, because write_cbor(el.first)
+                    // converts it to a temporary basic_json that would be
+                    // used as the context instead; for error_handler_t::keep
+                    // and ::replace/::ignore the recursive write_cbor(el.first)
+                    // call below handles the key like any other string, so no
+                    // separate check is needed here for those
+                    if (error_handler == error_handler_t::strict)
+                    {
+                        check_utf8(el.first, j);
+                    }
                     write_cbor(el.first);
                     write_cbor(el.second);
                 }
@@ -629,6 +656,8 @@ class binary_writer
     @param[in] add_prefix  whether prefixes need to be used for this value
     @param[in] use_bjdata  whether write in BJData format, default is false
     @param[in] bjdata_version  which BJData version to use, default is draft2
+    @throw type_error.316 if a string value or an object key is not valid
+           UTF-8
     */
     void write_ubjson(const BasicJsonType& j, const bool use_count,
                       const bool use_type, const bool add_prefix = true,
@@ -678,14 +707,17 @@ class binary_writer
 
             case value_t::string:
             {
+                string_t storage;
+                const string_t& value = sanitize_utf8_for_write(*j.m_data.m_value.string, j, storage);
+
                 if (add_prefix)
                 {
                     oa.write_character(to_char_type('S'));
                 }
-                write_number_with_ubjson_prefix(j.m_data.m_value.string->size(), true, use_bjdata);
+                write_number_with_ubjson_prefix(value.size(), true, use_bjdata);
                 oa.write_characters(
-                      reinterpret_cast<const CharType*>(j.m_data.m_value.string->data()),
-                      j.m_data.m_value.string->size());
+                      reinterpret_cast<const CharType*>(value.data()),
+                      value.size());
                 break;
             }
 
@@ -840,10 +872,12 @@ class binary_writer
 
                 for (const auto& el : *j.m_data.m_value.object)
                 {
-                    write_number_with_ubjson_prefix(el.first.size(), true, use_bjdata);
+                    string_t storage;
+                    const string_t& key = sanitize_utf8_for_write(el.first, j, storage);
+                    write_number_with_ubjson_prefix(key.size(), true, use_bjdata);
                     oa.write_characters(
-                          reinterpret_cast<const CharType*>(el.first.data()),
-                          el.first.size());
+                          reinterpret_cast<const CharType*>(key.data()),
+                          key.size());
                     write_ubjson(el.second, use_count, use_type, prefix_required, use_bjdata, bjdata_version);
                 }
 
@@ -884,8 +918,12 @@ class binary_writer
     /*!
     @return The size of a BSON document entry header, including the id marker
             and the entry name size (and its null-terminator).
+    @throw out_of_range.409 if @a name contains U+0000, before anything is
+           written
+    @throw type_error.316 if @a name is not valid UTF-8, before anything is
+           written
     */
-    static std::size_t calc_bson_entry_header_size(const string_t& name, const BasicJsonType& j)
+    std::size_t calc_bson_entry_header_size(const string_t& name, const BasicJsonType& j)
     {
         const auto it = name.find(static_cast<typename string_t::value_type>(0));
         if (JSON_HEDLEY_UNLIKELY(it != BasicJsonType::string_t::npos))
@@ -893,8 +931,10 @@ class binary_writer
             JSON_THROW(out_of_range::create(409, concat("BSON key cannot contain code point U+0000 (at byte ", std::to_string(it), ")"), &j));
         }
 
-        static_cast<void>(j);
-        return /*id*/ 1ul + name.size() + /*zero-terminator*/1u;
+        string_t storage;
+        const string_t& sanitized = sanitize_utf8_for_write(name, j, storage);
+
+        return /*id*/ 1ul + sanitized.size() + /*zero-terminator*/1u;
     }
 
     /*!
@@ -914,14 +954,28 @@ class binary_writer
 
     /*!
     @brief Writes the given @a element_type and @a name to the output adapter
+
+    @a name has already been validated (and, for @ref error_handler_t::strict,
+    found well-formed) by @ref calc_bson_entry_header_size during the earlier
+    size pass, so only @ref error_handler_t::replace / @ref
+    error_handler_t::ignore need to sanitize it again here, to actually write
+    the bytes that size was computed from.
     */
     void write_bson_entry_header(const string_t& name,
                                  const std::uint8_t element_type)
     {
         oa.write_character(to_char_type(element_type));
-        oa.write_characters(
-              reinterpret_cast<const CharType*>(name.data()),
-              name.size());
+
+        if (error_handler == error_handler_t::keep || error_handler == error_handler_t::strict || is_valid_utf8(name))
+        {
+            oa.write_characters(reinterpret_cast<const CharType*>(name.data()), name.size());
+        }
+        else
+        {
+            const string_t sanitized = sanitize_utf8(name, error_handler);
+            oa.write_characters(reinterpret_cast<const CharType*>(sanitized.data()), sanitized.size());
+        }
+
         // the terminating null byte is written explicitly rather than taken
         // from the buffer, so that string_t::data() need not be null-terminated
         oa.write_character(to_char_type(0x00));
@@ -949,24 +1003,50 @@ class binary_writer
 
     /*!
     @return The size of the BSON-encoded string in @a value
+    @throw type_error.316 if @a value is not valid UTF-8, before anything is
+           written
+
+    @note The UTF-8 check is skipped if @a value is already too long for the
+          32-bit BSON length field (@ref to_bson_length rejects it later, once
+          the size of the whole document is known); this also keeps the check
+          from reading past a StringType that reports a size larger than what
+          it actually holds.
     */
-    static std::size_t calc_bson_string_size(const string_t& value)
+    std::size_t calc_bson_string_size(const string_t& value, const BasicJsonType& j)
     {
+        if (JSON_HEDLEY_LIKELY(value_in_range_of<std::int32_t>(value.size())))
+        {
+            string_t storage;
+            const string_t& sanitized = sanitize_utf8_for_write(value, j, storage);
+            return sizeof(std::int32_t) + sanitized.size() + 1ul;
+        }
         return sizeof(std::int32_t) + value.size() + 1ul;
     }
 
     /*!
     @brief Writes a BSON element with key @a name and string value @a value
+
+    @a value has already been validated (and, for @ref error_handler_t::strict,
+    found well-formed) by @ref calc_bson_string_size during the earlier size
+    pass, so only @ref error_handler_t::replace / @ref error_handler_t::ignore
+    need to sanitize it again here, to actually write the bytes that size was
+    computed from.
     */
     void write_bson_string(const string_t& name,
                            const string_t& value)
     {
         write_bson_entry_header(name, 0x02);
 
-        write_number<std::int32_t>(to_bson_length(value.size() + 1ul), true);
+        const bool sanitize = error_handler != error_handler_t::keep
+                              && error_handler != error_handler_t::strict
+                              && !is_valid_utf8(value);
+        const string_t sanitized = sanitize ? sanitize_utf8(value, error_handler) : string_t{};
+        const string_t& written = sanitize ? sanitized : value;
+
+        write_number<std::int32_t>(to_bson_length(written.size() + 1ul), true);
         oa.write_characters(
-              reinterpret_cast<const CharType*>(value.data()),
-              value.size());
+              reinterpret_cast<const CharType*>(written.data()),
+              written.size());
         // the terminating null byte is written explicitly rather than taken
         // from the buffer, so that string_t::data() need not be null-terminated
         oa.write_character(to_char_type(0x00));
@@ -1080,8 +1160,10 @@ class binary_writer
             is neither an object nor an array
     @throw out_of_range.415 if @a j is binary with a subtype that does not fit
            into a byte, before anything is written
+    @throw type_error.316 if @a j is a string that is not valid UTF-8, before
+           anything is written
     */
-    static std::size_t calc_bson_value_size(const BasicJsonType& j)
+    std::size_t calc_bson_value_size(const BasicJsonType& j)
     {
         switch (j.type())
         {
@@ -1101,7 +1183,7 @@ class binary_writer
                 return calc_bson_unsigned_size(j.m_data.m_value.number_unsigned);
 
             case value_t::string:
-                return calc_bson_string_size(*j.m_data.m_value.string);
+                return calc_bson_string_size(*j.m_data.m_value.string, j);
 
             case value_t::null:
                 return 0ul;
@@ -1214,8 +1296,10 @@ class binary_writer
            written
     @throw out_of_range.415 if a binary value's subtype does not fit into a
            byte, before anything is written
+    @throw type_error.316 if a string value or a key is not valid UTF-8,
+           before anything is written
     */
-    static std::size_t calc_bson_sizes(const BasicJsonType& document, std::vector<std::size_t>& nested_sizes)
+    std::size_t calc_bson_sizes(const BasicJsonType& document, std::vector<std::size_t>& nested_sizes)
     {
         // the object or array whose entries are being sized, and the ones it
         // is in; nothing is allocated unless the document nests
@@ -2092,7 +2176,7 @@ class binary_writer
     */
     void write_bon8_string(const string_t& s, bool& string_open, const BasicJsonType& context)
     {
-        check_bon8_utf8(s, context);
+        check_utf8(s, context);
 
         // a string that follows another string terminates it
         if (string_open)
@@ -2122,7 +2206,7 @@ class binary_writer
     @throw type_error.316 if @a s is not valid UTF-8; the message names the
            first byte of the first invalid or incomplete sequence
     */
-    static void check_bon8_utf8(const string_t& s, const BasicJsonType& context)
+    static void check_utf8(const string_t& s, const BasicJsonType& context)
     {
         static_cast<void>(context); // only used when exceptions are enabled
         const auto* data = reinterpret_cast<const unsigned char*>(s.data());
@@ -2133,6 +2217,59 @@ class binary_writer
         }
     }
 
+    /*!
+    @brief return @a s as it should be written, honoring @ref error_handler
+
+    Used by @ref write_cbor, @ref write_ubjson (and so @ref write_bjdata), and
+    the BSON writing functions for string values and object keys; never by
+    @ref write_msgpack or @ref write_bon8, which do not take an @ref
+    error_handler (MessagePack's spec allows a str object to contain
+    ill-formed UTF-8, and BON8 always validates, since UTF-8 lead bytes are
+    structural there).
+
+    - @ref error_handler_t::keep: @a s is returned unchanged, without even
+      checking it (the behavior of release 3.12.0 and earlier).
+    - @ref error_handler_t::strict: @ref check_utf8 is called, which throws
+      type_error.316 if @a s is not valid UTF-8.
+    - @ref error_handler_t::replace / @ref error_handler_t::ignore: @a s is
+      sanitized into @a storage with exactly the rules @ref
+      serializer::dump_escaped_impl uses, so that parsing what @ref
+      basic_json::dump produces for the same string and the same handler
+      yields the same result.
+
+    Well-formed input is never copied: this returns a reference to @a s
+    itself in every case but a sanitized `replace`/`ignore` one, so @a
+    storage must outlive the returned reference only then.
+
+    @param[in] s        the string (value or object key) to write
+    @param[in] context  the value @a s belongs to (for diagnostics)
+    @param[out] storage  backing storage for a sanitized copy
+
+    @return a reference to @a s, or to @a storage once it holds a sanitized copy
+    */
+    const string_t& sanitize_utf8_for_write(const string_t& s, const BasicJsonType& context, string_t& storage) const
+    {
+        switch (error_handler)
+        {
+            case error_handler_t::keep:
+                return s;
+
+            case error_handler_t::strict:
+                check_utf8(s, context);
+                return s;
+
+            case error_handler_t::replace:
+            case error_handler_t::ignore:
+            default:
+                if (is_valid_utf8(s))
+                {
+                    return s;
+                }
+                storage = sanitize_utf8(s, error_handler);
+                return storage;
+        }
+    }
+
     /*!
     @brief write an integer in the shortest encoding
 
@@ -2461,6 +2598,10 @@ class binary_writer
 
     /// the output
     OutputSinkType oa;
+
+    /// how to treat a string value or object key that is not valid UTF-8
+    /// (CBOR, UBJSON, BJData, and BSON only)
+    const error_handler_t error_handler = error_handler_t::strict;
 };
 
 }  // namespace detail

include/nlohmann/detail/output/error_handler.hpp

@@ -0,0 +1,38 @@
+//     __ _____ _____ _____
+//  __|  |   __|     |   | |  JSON for Modern C++
+// |  |  |__   |  |  | | | |  version 3.12.0
+// |_____|_____|_____|_|___|  https://github.com/nlohmann/json
+//
+// SPDX-FileCopyrightText: 2013-2026 Niels Lohmann <https://nlohmann.me>
+// SPDX-License-Identifier: MIT
+
+#pragma once
+
+#include <nlohmann/detail/abi_macros.hpp>
+
+NLOHMANN_JSON_NAMESPACE_BEGIN
+namespace detail
+{
+
+/// how to treat decoding errors
+///
+/// @ref basic_json::dump uses this to decide what to do with ill-formed
+/// UTF-8 while escaping a string, and the binary writers (@ref
+/// basic_json::to_cbor, @ref basic_json::to_ubjson, @ref
+/// basic_json::to_bjdata, @ref basic_json::to_bson) use it the same way for
+/// string values and object keys. The binary readers (@ref
+/// basic_json::from_cbor, @ref basic_json::from_msgpack, @ref
+/// basic_json::from_ubjson, @ref basic_json::from_bjdata, @ref
+/// basic_json::from_bson) use it to decide whether to check text strings
+/// and object keys for well-formed UTF-8 at all, since none of those
+/// formats requires a decoder to do so.
+enum class error_handler_t
+{
+    strict,  ///< throw a type_error/parse_error exception in case of invalid UTF-8
+    replace, ///< replace invalid UTF-8 sequences with U+FFFD
+    ignore,  ///< ignore invalid UTF-8 sequences
+    keep     ///< keep invalid UTF-8 sequences unchanged
+};
+
+}  // namespace detail
+NLOHMANN_JSON_NAMESPACE_END

include/nlohmann/detail/output/serializer.hpp

@@ -27,6 +27,7 @@
 #include <nlohmann/detail/input/string_scan.hpp>
 #include <nlohmann/detail/macro_scope.hpp>
 #include <nlohmann/detail/meta/cpp_future.hpp>
+#include <nlohmann/detail/output/error_handler.hpp>
 #include <nlohmann/detail/output/output_adapters.hpp>
 #include <nlohmann/detail/recursion_depth_limit.hpp>
 #include <nlohmann/detail/string_concat.hpp>
@@ -41,14 +42,6 @@ namespace detail
 // serialization //
 ///////////////////
 
-/// how to treat decoding errors
-enum class error_handler_t
-{
-    strict,  ///< throw a type_error exception in case of invalid UTF-8
-    replace, ///< replace invalid UTF-8 sequences with U+FFFD
-    ignore   ///< ignore invalid UTF-8 sequences
-};
-
 template<typename BasicJsonType>
 class serializer
 {
@@ -839,6 +832,16 @@ class serializer
                             // EnsureAscii parameter is used, non-ASCII characters
                             if ((codepoint <= 0x1F) || (EnsureAscii && (codepoint >= 0x7F)))
                             {
+                                if (EnsureAscii && error_handler == error_handler_t::keep)
+                                {
+                                    // this character was buffered as raw bytes
+                                    // below in case it turned out to be part of
+                                    // an ill-formed sequence (which is kept as
+                                    // is); now that it decoded to a well-formed
+                                    // code point, undo that and \u-escape it
+                                    // like any other character instead
+                                    bytes = bytes_after_last_accept;
+                                }
                                 if (codepoint <= 0xFFFF)
                                 {
                                     write_u_escape(bytes, static_cast<std::uint16_t>(codepoint));
@@ -937,6 +940,44 @@ class serializer
                             break;
                         }
 
+                        case error_handler_t::keep:
+                        {
+                            // the bytes of this (now abandoned) ill-formed
+                            // sequence seen so far are already buffered below
+                            // and are kept unchanged in the output
+                            if (undumped_chars > 0)
+                            {
+                                // the byte that ended the sequence may be OK
+                                // for itself (e.g., a quote that must still be
+                                // escaped, or the lead byte of a well-formed
+                                // code point), so read it again
+                                --i;
+                            }
+                            else
+                            {
+                                // a byte that cannot start a sequence (e.g.,
+                                // 0xFF or a stray continuation byte) is kept
+                                // as well
+                                string_buffer[bytes++] = s[i];
+                            }
+
+                            // write buffer and reset index; there must be 13 bytes
+                            // left, as this is the maximal number of bytes to be
+                            // written ("\uxxxx\uxxxx\0") for one code point
+                            if (string_buffer.size() - bytes < 13)
+                            {
+                                put_buffer(string_buffer, bytes);
+                                bytes = 0;
+                            }
+
+                            bytes_after_last_accept = bytes;
+                            undumped_chars = 0;
+
+                            // continue processing the string
+                            state = UTF8_ACCEPT;
+                            break;
+                        }
+
                         default:            // LCOV_EXCL_LINE
                             JSON_ASSERT(false); // NOLINT(cert-dcl03-c,hicpp-static-assert,misc-static-assert) LCOV_EXCL_LINE
                     }
@@ -945,9 +986,12 @@ class serializer
 
                 default:  // decode found yet incomplete multibyte code point
                 {
-                    if (!EnsureAscii)
+                    if (!EnsureAscii || error_handler == error_handler_t::keep)
                     {
-                        // code point will not be escaped - copy byte to buffer
+                        // code point will not be escaped (or will be kept as
+                        // is if it turns out to be ill-formed) - copy byte to
+                        // buffer; dropped again above if it decodes to a
+                        // well-formed code point that needs \u-escaping
                         string_buffer[bytes++] = s[i];
                     }
                     ++undumped_chars;
@@ -998,6 +1042,14 @@ class serializer
                     break;
                 }
 
+                case error_handler_t::keep:
+                {
+                    // write the ill-formed trailing bytes as is; they were
+                    // buffered above regardless of EnsureAscii
+                    put_buffer(string_buffer, bytes);
+                    break;
+                }
+
                 default:            // LCOV_EXCL_LINE
                     JSON_ASSERT(false); // NOLINT(cert-dcl03-c,hicpp-static-assert,misc-static-assert) LCOV_EXCL_LINE
             }

include/nlohmann/detail/string_utils.hpp

@@ -16,6 +16,7 @@
 
 #include <nlohmann/detail/abi_macros.hpp>
 #include <nlohmann/detail/macro_scope.hpp>
+#include <nlohmann/detail/output/error_handler.hpp>
 
 NLOHMANN_JSON_NAMESPACE_BEGIN
 namespace detail
@@ -117,13 +118,14 @@ This is a single-byte step of a "shift-based" UTF-8 decoder originally
 written by Björn Hoehrmann. See
 http://bjoern.hoehrmann.de/utf-8/decoder/dfa/ for details.
 
-The library checks UTF-8 well-formedness (RFC 3629, section 4) in four
+The library checks UTF-8 well-formedness (RFC 3629, section 4) in three
 places, which differ in speed, diagnostics, and how they read the input:
 
-- decode() and @ref is_valid_utf8 below: the serializer (to escape and, in
-  strict mode, reject ill-formed UTF-8 when dumping a string) and the CBOR,
-  MessagePack, BSON, UBJSON and BJData readers (to reject ill-formed UTF-8 in
-  text strings at decode time).
+- decode() below: the serializer, to escape and, in strict mode, reject
+  ill-formed UTF-8 when dumping a string. The CBOR, MessagePack, BSON,
+  UBJSON and BJData readers do not use it: none of those specs requires a
+  decoder to reject ill-formed UTF-8 in text strings, so the readers keep
+  the bytes as is and leave the check to dump() and the binary writers.
 - the per-lead-byte switch in lexer::scan_string(): JSON text, with a
   diagnostic for each kind of error.
 - validate_one_utf8() and valid_utf8_prefix() in string_scan.hpp: the lexer's
@@ -179,19 +181,19 @@ inline std::uint8_t decode(std::uint8_t& state, std::uint32_t& codep, const std:
 }
 
 /*!
-@brief check whether a string consists solely of valid UTF-8
+@brief check a string for well-formed UTF-8 (RFC 3629, section 4)
 
-Used by the CBOR/MessagePack/BSON/UBJSON binary readers to reject text
-strings that are not valid UTF-8 at decode time (RFC 8949 §3.1 and the
-MessagePack/BSON specifications all require text strings to be UTF-8), so
-that malformed input is caught immediately instead of only surfacing later
-as a type_error.316 when the resulting value is dumped.
+Used by the binary readers (CBOR, MessagePack, UBJSON, BJData, BSON) when an
+@ref error_handler_t other than `keep` is requested for a text string value
+or object key: none of those formats requires a decoder to reject ill-formed
+UTF-8 on its own, so the check is opt-in there, unlike the JSON lexer and the
+serializer's @ref decode -based escaping, which always run it.
 
 @param[in] s      the string to check
-@param[in] first  index of the first byte to check; the bytes before it are
-                  assumed to have been validated already and to end on a
-                  code point boundary
-@return whether @a s (from index @a first on) is valid UTF-8
+@param[in] first  the index to start checking at
+@return whether `s.substr(first)` is well-formed UTF-8
+
+@sa @ref decode
 */
 template<typename StringType>
 inline bool is_valid_utf8(const StringType& s, const std::size_t first = 0) noexcept
@@ -211,5 +213,101 @@ inline bool is_valid_utf8(const StringType& s, const std::size_t first = 0) noex
     return state == UTF8_ACCEPT;
 }
 
+/*!
+@brief sanitize a string with ill-formed UTF-8 for @ref error_handler_t::replace or @ref error_handler_t::ignore
+
+Replaces every maximal ill-formed subsequence with U+FFFD (`replace`) or
+drops it (`ignore`), using exactly the same boundaries @ref
+serializer::dump_escaped_impl uses while escaping a string: a byte that does
+not extend the sequence started by the previous byte(s) is reread as the
+start of a new one, instead of being swallowed along with them.
+
+@pre @a error_handler is @ref error_handler_t::replace or @ref error_handler_t::ignore
+@note Well-formed input is copied through unchanged, including bytes (e.g.
+      control characters or quotes) that @ref serializer::dump_escaped_impl
+      would itself escape; this function only concerns itself with
+      well-formedness, not with producing valid JSON text.
+
+@param[in] s              the string to sanitize
+@param[in] error_handler  @ref error_handler_t::replace or @ref error_handler_t::ignore
+
+@return @a s with every ill-formed subsequence replaced or removed
+
+@sa @ref decode
+*/
+template<typename StringType>
+inline StringType sanitize_utf8(const StringType& s, const error_handler_t error_handler)
+{
+    JSON_ASSERT(error_handler == error_handler_t::replace || error_handler == error_handler_t::ignore);
+
+    StringType result;
+    result.reserve(s.size());
+
+    std::uint32_t codepoint = 0;
+    std::uint8_t state = UTF8_ACCEPT;
+    // length of result after the last accepted code point
+    std::size_t result_len_after_last_accept = 0;
+    // whether bytes of an as yet unresolved sequence were already appended
+    bool pending = false;
+
+    for (std::size_t i = 0; i < s.size(); ++i)
+    {
+        switch (decode(state, codepoint, static_cast<std::uint8_t>(s[i])))
+        {
+            case UTF8_ACCEPT: // decode found a well-formed code point
+            {
+                result.push_back(s[i]);
+                result_len_after_last_accept = result.size();
+                pending = false;
+                break;
+            }
+
+            case UTF8_REJECT: // decode found an ill-formed byte
+            {
+                // in case we saw this byte for the first time, read it again,
+                // because it may be fine for itself, just not for the
+                // sequence that came before it
+                if (pending)
+                {
+                    --i;
+                }
+
+                // drop the bytes of the ill-formed sequence buffered below
+                result.resize(result_len_after_last_accept);
+
+                if (error_handler == error_handler_t::replace)
+                {
+                    result.append("\xEF\xBF\xBD");
+                    result_len_after_last_accept = result.size();
+                }
+
+                pending = false;
+                state = UTF8_ACCEPT;
+                break;
+            }
+
+            default: // decode found yet incomplete multibyte code point
+            {
+                result.push_back(s[i]);
+                pending = true;
+                break;
+            }
+        }
+    }
+
+    // the string ended with an incomplete sequence
+    if (state != UTF8_ACCEPT)
+    {
+        result.resize(result_len_after_last_accept);
+
+        if (error_handler == error_handler_t::replace)
+        {
+            result.append("\xEF\xBF\xBD");
+        }
+    }
+
+    return result;
+}
+
 }  // namespace detail
 NLOHMANN_JSON_NAMESPACE_END

include/nlohmann/json.hpp

@@ -201,9 +201,10 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
     // used by the vector-returning to_* overloads
     template<typename CharType> using vector_binary_writer =
         ::nlohmann::detail::binary_writer<basic_json, CharType, ::nlohmann::detail::output_vector_sink<CharType>>;
-    template<typename CharType> static vector_binary_writer<CharType> vector_writer(std::vector<CharType>& v)
+    template<typename CharType> static vector_binary_writer<CharType> vector_writer(
+        std::vector<CharType>& v, const ::nlohmann::detail::error_handler_t error_handler = ::nlohmann::detail::error_handler_t::strict)
     {
-        return vector_binary_writer<CharType>(::nlohmann::detail::output_vector_sink<CharType>(v));
+        return vector_binary_writer<CharType>(::nlohmann::detail::output_vector_sink<CharType>(v), error_handler);
     }
 
   JSON_PRIVATE_UNLESS_TESTED:
@@ -5445,26 +5446,29 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
   public:
     /// @brief create a CBOR serialization of a given JSON value
     /// @sa https://json.nlohmann.me/api/basic_json/to_cbor/
-    static std::vector<std::uint8_t> to_cbor(const basic_json& j)
+    static std::vector<std::uint8_t> to_cbor(const basic_json& j,
+            const error_handler_t error_handler = error_handler_t::strict)
     {
         std::vector<std::uint8_t> result;
         result.reserve(detail::binary_reserve_hint(j));
-        vector_writer(result).write_cbor(j);
+        vector_writer(result, error_handler).write_cbor(j);
         return result;
     }
 
     /// @brief create a CBOR serialization of a given JSON value
     /// @sa https://json.nlohmann.me/api/basic_json/to_cbor/
-    static void to_cbor(const basic_json& j, detail::output_adapter<std::uint8_t> o)
+    static void to_cbor(const basic_json& j, detail::output_adapter<std::uint8_t> o,
+                        const error_handler_t error_handler = error_handler_t::strict)
     {
-        binary_writer<std::uint8_t>(o).write_cbor(j);
+        binary_writer<std::uint8_t>(o, error_handler).write_cbor(j);
     }
 
     /// @brief create a CBOR serialization of a given JSON value
     /// @sa https://json.nlohmann.me/api/basic_json/to_cbor/
-    static void to_cbor(const basic_json& j, detail::output_adapter<char> o)
+    static void to_cbor(const basic_json& j, detail::output_adapter<char> o,
+                        const error_handler_t error_handler = error_handler_t::strict)
     {
-        binary_writer<char>(o).write_cbor(j);
+        binary_writer<char>(o, error_handler).write_cbor(j);
     }
 
     /// @brief create a MessagePack serialization of a given JSON value
@@ -5495,28 +5499,31 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
     /// @sa https://json.nlohmann.me/api/basic_json/to_ubjson/
     static std::vector<std::uint8_t> to_ubjson(const basic_json& j,
             const bool use_size = false,
-            const bool use_type = false)
+            const bool use_type = false,
+            const error_handler_t error_handler = error_handler_t::strict)
     {
         std::vector<std::uint8_t> result;
         result.reserve(detail::binary_reserve_hint(j));
-        vector_writer(result).write_ubjson(j, use_size, use_type);
+        vector_writer(result, error_handler).write_ubjson(j, use_size, use_type);
         return result;
     }
 
     /// @brief create a UBJSON serialization of a given JSON value
     /// @sa https://json.nlohmann.me/api/basic_json/to_ubjson/
     static void to_ubjson(const basic_json& j, detail::output_adapter<std::uint8_t> o,
-                          const bool use_size = false, const bool use_type = false)
+                          const bool use_size = false, const bool use_type = false,
+                          const error_handler_t error_handler = error_handler_t::strict)
     {
-        binary_writer<std::uint8_t>(o).write_ubjson(j, use_size, use_type);
+        binary_writer<std::uint8_t>(o, error_handler).write_ubjson(j, use_size, use_type);
     }
 
     /// @brief create a UBJSON serialization of a given JSON value
     /// @sa https://json.nlohmann.me/api/basic_json/to_ubjson/
     static void to_ubjson(const basic_json& j, detail::output_adapter<char> o,
-                          const bool use_size = false, const bool use_type = false)
+                          const bool use_size = false, const bool use_type = false,
+                          const error_handler_t error_handler = error_handler_t::strict)
     {
-        binary_writer<char>(o).write_ubjson(j, use_size, use_type);
+        binary_writer<char>(o, error_handler).write_ubjson(j, use_size, use_type);
     }
 
     /// @brief create a BJData serialization of a given JSON value
@@ -5524,11 +5531,12 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
     static std::vector<std::uint8_t> to_bjdata(const basic_json& j,
             const bool use_size = false,
             const bool use_type = false,
-            const bjdata_version_t version = bjdata_version_t::draft2)
+            const bjdata_version_t version = bjdata_version_t::draft2,
+            const error_handler_t error_handler = error_handler_t::strict)
     {
         std::vector<std::uint8_t> result;
         result.reserve(detail::binary_reserve_hint(j));
-        vector_writer(result).write_ubjson(j, use_size, use_type, true, true, version);
+        vector_writer(result, error_handler).write_ubjson(j, use_size, use_type, true, true, version);
         return result;
     }
 
@@ -5536,42 +5544,47 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
     /// @sa https://json.nlohmann.me/api/basic_json/to_bjdata/
     static void to_bjdata(const basic_json& j, detail::output_adapter<std::uint8_t> o,
                           const bool use_size = false, const bool use_type = false,
-                          const bjdata_version_t version = bjdata_version_t::draft2)
+                          const bjdata_version_t version = bjdata_version_t::draft2,
+                          const error_handler_t error_handler = error_handler_t::strict)
     {
-        binary_writer<std::uint8_t>(o).write_ubjson(j, use_size, use_type, true, true, version);
+        binary_writer<std::uint8_t>(o, error_handler).write_ubjson(j, use_size, use_type, true, true, version);
     }
 
     /// @brief create a BJData serialization of a given JSON value
     /// @sa https://json.nlohmann.me/api/basic_json/to_bjdata/
     static void to_bjdata(const basic_json& j, detail::output_adapter<char> o,
                           const bool use_size = false, const bool use_type = false,
-                          const bjdata_version_t version = bjdata_version_t::draft2)
+                          const bjdata_version_t version = bjdata_version_t::draft2,
+                          const error_handler_t error_handler = error_handler_t::strict)
     {
-        binary_writer<char>(o).write_ubjson(j, use_size, use_type, true, true, version);
+        binary_writer<char>(o, error_handler).write_ubjson(j, use_size, use_type, true, true, version);
     }
 
     /// @brief create a BSON serialization of a given JSON value
     /// @sa https://json.nlohmann.me/api/basic_json/to_bson/
-    static std::vector<std::uint8_t> to_bson(const basic_json& j)
+    static std::vector<std::uint8_t> to_bson(const basic_json& j,
+            const error_handler_t error_handler = error_handler_t::strict)
     {
         std::vector<std::uint8_t> result;
         result.reserve(detail::binary_reserve_hint(j));
-        vector_writer(result).write_bson(j);
+        vector_writer(result, error_handler).write_bson(j);
         return result;
     }
 
     /// @brief create a BSON serialization of a given JSON value
     /// @sa https://json.nlohmann.me/api/basic_json/to_bson/
-    static void to_bson(const basic_json& j, detail::output_adapter<std::uint8_t> o)
+    static void to_bson(const basic_json& j, detail::output_adapter<std::uint8_t> o,
+                        const error_handler_t error_handler = error_handler_t::strict)
     {
-        binary_writer<std::uint8_t>(o).write_bson(j);
+        binary_writer<std::uint8_t>(o, error_handler).write_bson(j);
     }
 
     /// @brief create a BSON serialization of a given JSON value
     /// @sa https://json.nlohmann.me/api/basic_json/to_bson/
-    static void to_bson(const basic_json& j, detail::output_adapter<char> o)
+    static void to_bson(const basic_json& j, detail::output_adapter<char> o,
+                        const error_handler_t error_handler = error_handler_t::strict)
     {
-        binary_writer<char>(o).write_bson(j);
+        binary_writer<char>(o, error_handler).write_bson(j);
     }
 
     /// @brief create a BON8 serialization of a given JSON value
@@ -5605,12 +5618,13 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
     static basic_json from_cbor(InputType&& i,
                                 const bool strict = true,
                                 const bool allow_exceptions = true,
-                                const cbor_tag_handler_t tag_handler = cbor_tag_handler_t::error)
+                                const cbor_tag_handler_t tag_handler = cbor_tag_handler_t::error,
+                                const error_handler_t error_handler = error_handler_t::keep)
     {
         basic_json result;
         auto ia = detail::input_adapter(std::forward<InputType>(i));
         detail::json_sax_dom_parser<basic_json, decltype(ia)> sdp(result, allow_exceptions);
-        if (!binary_reader<decltype(ia)>(std::move(ia), input_format_t::cbor).sax_parse(&sdp, strict, tag_handler)) // cppcheck-suppress[accessMoved]
+        if (!binary_reader<decltype(ia)>(std::move(ia), input_format_t::cbor, error_handler).sax_parse(&sdp, strict, tag_handler)) // cppcheck-suppress[accessMoved]
         {
             result = value_t::discarded;
         }
@@ -5625,12 +5639,13 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
     static basic_json from_cbor(IteratorType first, SentinelType last,
                                 const bool strict = true,
                                 const bool allow_exceptions = true,
-                                const cbor_tag_handler_t tag_handler = cbor_tag_handler_t::error)
+                                const cbor_tag_handler_t tag_handler = cbor_tag_handler_t::error,
+                                const error_handler_t error_handler = error_handler_t::keep)
     {
         basic_json result;
         auto ia = detail::input_adapter(std::move(first), std::move(last));
         detail::json_sax_dom_parser<basic_json, decltype(ia)> sdp(result, allow_exceptions);
-        if (!binary_reader<decltype(ia)>(std::move(ia), input_format_t::cbor).sax_parse(&sdp, strict, tag_handler)) // cppcheck-suppress[accessMoved]
+        if (!binary_reader<decltype(ia)>(std::move(ia), input_format_t::cbor, error_handler).sax_parse(&sdp, strict, tag_handler)) // cppcheck-suppress[accessMoved]
         {
             result = value_t::discarded;
         }
@@ -5672,12 +5687,13 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
     JSON_HEDLEY_WARN_UNUSED_RESULT
     static basic_json from_msgpack(InputType&& i,
                                    const bool strict = true,
-                                   const bool allow_exceptions = true)
+                                   const bool allow_exceptions = true,
+                                   const error_handler_t error_handler = error_handler_t::keep)
     {
         basic_json result;
         auto ia = detail::input_adapter(std::forward<InputType>(i));
         detail::json_sax_dom_parser<basic_json, decltype(ia)> sdp(result, allow_exceptions);
-        if (!binary_reader<decltype(ia)>(std::move(ia), input_format_t::msgpack).sax_parse(&sdp, strict)) // cppcheck-suppress[accessMoved]
+        if (!binary_reader<decltype(ia)>(std::move(ia), input_format_t::msgpack, error_handler).sax_parse(&sdp, strict)) // cppcheck-suppress[accessMoved]
         {
             result = value_t::discarded;
         }
@@ -5691,12 +5707,13 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
     JSON_HEDLEY_WARN_UNUSED_RESULT
     static basic_json from_msgpack(IteratorType first, SentinelType last,
                                    const bool strict = true,
-                                   const bool allow_exceptions = true)
+                                   const bool allow_exceptions = true,
+                                   const error_handler_t error_handler = error_handler_t::keep)
     {
         basic_json result;
         auto ia = detail::input_adapter(std::move(first), std::move(last));
         detail::json_sax_dom_parser<basic_json, decltype(ia)> sdp(result, allow_exceptions);
-        if (!binary_reader<decltype(ia)>(std::move(ia), input_format_t::msgpack).sax_parse(&sdp, strict)) // cppcheck-suppress[accessMoved]
+        if (!binary_reader<decltype(ia)>(std::move(ia), input_format_t::msgpack, error_handler).sax_parse(&sdp, strict)) // cppcheck-suppress[accessMoved]
         {
             result = value_t::discarded;
         }
@@ -5736,12 +5753,13 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
     JSON_HEDLEY_WARN_UNUSED_RESULT
     static basic_json from_ubjson(InputType&& i,
                                   const bool strict = true,
-                                  const bool allow_exceptions = true)
+                                  const bool allow_exceptions = true,
+                                  const error_handler_t error_handler = error_handler_t::keep)
     {
         basic_json result;
         auto ia = detail::input_adapter(std::forward<InputType>(i));
         detail::json_sax_dom_parser<basic_json, decltype(ia)> sdp(result, allow_exceptions);
-        if (!binary_reader<decltype(ia)>(std::move(ia), input_format_t::ubjson).sax_parse(&sdp, strict)) // cppcheck-suppress[accessMoved]
+        if (!binary_reader<decltype(ia)>(std::move(ia), input_format_t::ubjson, error_handler).sax_parse(&sdp, strict)) // cppcheck-suppress[accessMoved]
         {
             result = value_t::discarded;
         }
@@ -5755,12 +5773,13 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
     JSON_HEDLEY_WARN_UNUSED_RESULT
     static basic_json from_ubjson(IteratorType first, SentinelType last,
                                   const bool strict = true,
-                                  const bool allow_exceptions = true)
+                                  const bool allow_exceptions = true,
+                                  const error_handler_t error_handler = error_handler_t::keep)
     {
         basic_json result;
         auto ia = detail::input_adapter(std::move(first), std::move(last));
         detail::json_sax_dom_parser<basic_json, decltype(ia)> sdp(result, allow_exceptions);
-        if (!binary_reader<decltype(ia)>(std::move(ia), input_format_t::ubjson).sax_parse(&sdp, strict)) // cppcheck-suppress[accessMoved]
+        if (!binary_reader<decltype(ia)>(std::move(ia), input_format_t::ubjson, error_handler).sax_parse(&sdp, strict)) // cppcheck-suppress[accessMoved]
         {
             result = value_t::discarded;
         }
@@ -5800,12 +5819,13 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
     JSON_HEDLEY_WARN_UNUSED_RESULT
     static basic_json from_bjdata(InputType&& i,
                                   const bool strict = true,
-                                  const bool allow_exceptions = true)
+                                  const bool allow_exceptions = true,
+                                  const error_handler_t error_handler = error_handler_t::keep)
     {
         basic_json result;
         auto ia = detail::input_adapter(std::forward<InputType>(i));
         detail::json_sax_dom_parser<basic_json, decltype(ia)> sdp(result, allow_exceptions);
-        if (!binary_reader<decltype(ia)>(std::move(ia), input_format_t::bjdata).sax_parse(&sdp, strict)) // cppcheck-suppress[accessMoved]
+        if (!binary_reader<decltype(ia)>(std::move(ia), input_format_t::bjdata, error_handler).sax_parse(&sdp, strict)) // cppcheck-suppress[accessMoved]
         {
             result = value_t::discarded;
         }
@@ -5819,12 +5839,13 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
     JSON_HEDLEY_WARN_UNUSED_RESULT
     static basic_json from_bjdata(IteratorType first, SentinelType last,
                                   const bool strict = true,
-                                  const bool allow_exceptions = true)
+                                  const bool allow_exceptions = true,
+                                  const error_handler_t error_handler = error_handler_t::keep)
     {
         basic_json result;
         auto ia = detail::input_adapter(std::move(first), std::move(last));
         detail::json_sax_dom_parser<basic_json, decltype(ia)> sdp(result, allow_exceptions);
-        if (!binary_reader<decltype(ia)>(std::move(ia), input_format_t::bjdata).sax_parse(&sdp, strict)) // cppcheck-suppress[accessMoved]
+        if (!binary_reader<decltype(ia)>(std::move(ia), input_format_t::bjdata, error_handler).sax_parse(&sdp, strict)) // cppcheck-suppress[accessMoved]
         {
             result = value_t::discarded;
         }
@@ -5874,12 +5895,13 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
     JSON_HEDLEY_WARN_UNUSED_RESULT
     static basic_json from_bson(InputType&& i,
                                 const bool strict = true,
-                                const bool allow_exceptions = true)
+                                const bool allow_exceptions = true,
+                                const error_handler_t error_handler = error_handler_t::keep)
     {
         basic_json result;
         auto ia = detail::input_adapter(std::forward<InputType>(i));
         detail::json_sax_dom_parser<basic_json, decltype(ia)> sdp(result, allow_exceptions);
-        if (!binary_reader<decltype(ia)>(std::move(ia), input_format_t::bson).sax_parse(&sdp, strict)) // cppcheck-suppress[accessMoved]
+        if (!binary_reader<decltype(ia)>(std::move(ia), input_format_t::bson, error_handler).sax_parse(&sdp, strict)) // cppcheck-suppress[accessMoved]
         {
             result = value_t::discarded;
         }
@@ -5893,12 +5915,13 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
     JSON_HEDLEY_WARN_UNUSED_RESULT
     static basic_json from_bson(IteratorType first, SentinelType last,
                                 const bool strict = true,
-                                const bool allow_exceptions = true)
+                                const bool allow_exceptions = true,
+                                const error_handler_t error_handler = error_handler_t::keep)
     {
         basic_json result;
         auto ia = detail::input_adapter(std::move(first), std::move(last));
         detail::json_sax_dom_parser<basic_json, decltype(ia)> sdp(result, allow_exceptions);
-        if (!binary_reader<decltype(ia)>(std::move(ia), input_format_t::bson).sax_parse(&sdp, strict)) // cppcheck-suppress[accessMoved]
+        if (!binary_reader<decltype(ia)>(std::move(ia), input_format_t::bson, error_handler).sax_parse(&sdp, strict)) // cppcheck-suppress[accessMoved]
         {
             result = value_t::discarded;
         }

tests/src/float_hard_cases.hpp

@@ -1,599 +0,0 @@
-//     __ _____ _____ _____
-//  __|  |   __|     |   | |  JSON for Modern C++ (supporting code)
-// |  |  |__   |  |  | | | |  version 3.12.0
-// |_____|_____|_____|_|___|  https://github.com/nlohmann/json
-//
-// SPDX-FileCopyrightText: 2013-2026 Niels Lohmann <https://nlohmann.me>
-// SPDX-License-Identifier: MIT
-
-#pragma once
-
-#include <array> // array
-#include <cstdint> // uint32_t, uint64_t
-
-// Number tokens that are hard to round correctly, with the IEEE-754 binary64
-// and binary32 bits of their correctly rounded values (ties to even; infinity
-// for an overflow, a signed zero for an underflow).
-//
-// For doubles and floats around 0, the smallest normal number, 1, 2^24, 2^53,
-// 0.1, and the largest finite number, and for random ones, the exact midpoint
-// m to the next number gives: m, m with one unit more and less in the last
-// digit, m with "01" and "0...01" appended, m with trailing zeros, and m cut
-// after 17 to 30 digits (rounded down and up, so that the rounding is decided
-// after the 19th digit), in fixed and exponent notation, 30% of them negative.
-// Tokens longer than 80 characters are left out, except for four of 700 digits
-// and more. Zeros, underflow, overflow, huge exponents, and integers beyond 64
-// bits complete the set. Of the 508 tokens, 134 (as double) and 150 (as
-// float) need the exact comparison with the midpoint (detail::digit_comparison()).
-//
-// The expected bits were computed with exact rational arithmetic in Python
-// (fractions.Fraction) and cross-checked with Python's float(); strtod_l and
-// strtof_l of Apple's libc and of glibc agree. Generated by
-// compact_hard_cases.py 5 (with hard_cases.py), see the pull request that
-// added this file.
-
-namespace float_hard_cases
-{
-
-struct hard_case
-{
-    const char* token;
-    std::uint64_t bits64;
-    std::uint32_t bits32;
-};
-
-inline const std::array<hard_case, 508>& cases()
-{
-    static const std::array<hard_case, 508> table =
-    {
-        {
-            {"-2.4703282292062327e-324", 0x8000000000000000u, 0x80000000u},
-            {"24703282292062328e-340", 0x0000000000000001u, 0x00000000u},
-            {"247032822920623272e-341", 0x0000000000000000u, 0x00000000u},
-            {"-0.2470328229206232721e-323", 0x8000000000000001u, 0x80000000u},
-            {"-0.24703282292062327208e-323", 0x8000000000000000u, 0x80000000u},
-            {"-2.4703282292062327209e-324", 0x8000000000000001u, 0x80000000u},
-            {"2.47032822920623272088e-324", 0x0000000000000000u, 0x00000000u},
-            {"247032822920623272089e-344", 0x0000000000000001u, 0x00000000u},
-            {"-247032822920623272088284396434e-353", 0x8000000000000000u, 0x80000000u},
-            {"0.247032822920623272088284396435e-323", 0x0000000000000001u, 0x00000000u},
-            {"-74109846876186981e-340", 0x8000000000000001u, 0x80000000u},
-            {"0.74109846876186982e-323", 0x0000000000000002u, 0x00000000u},
-            {"-0.7410984687618698162e-323", 0x8000000000000001u, 0x80000000u},
-            {"-7.410984687618698163e-324", 0x8000000000000002u, 0x80000000u},
-            {"7.4109846876186981626e-324", 0x0000000000000001u, 0x00000000u},
-            {"-74109846876186981627e-343", 0x8000000000000002u, 0x80000000u},
-            {"-741098468761869816264e-344", 0x8000000000000001u, 0x80000000u},
-            {"0.741098468761869816265e-323", 0x0000000000000002u, 0x00000000u},
-            {"0.741098468761869816264853189302e-323", 0x0000000000000001u, 0x00000000u},
-            {"-7.41098468761869816264853189303e-324", 0x8000000000000002u, 0x80000000u},
-            {"0.22250738585072006e-307", 0x000FFFFFFFFFFFFEu, 0x00000000u},
-            {"2.2250738585072007e-308", 0x000FFFFFFFFFFFFFu, 0x00000000u},
-            {"2.225073858507200641e-308", 0x000FFFFFFFFFFFFEu, 0x00000000u},
-            {"-2225073858507200642e-326", 0x800FFFFFFFFFFFFFu, 0x80000000u},
-            {"22250738585072006419e-327", 0x000FFFFFFFFFFFFEu, 0x00000000u},
-            {"0.2225073858507200642e-307", 0x000FFFFFFFFFFFFFu, 0x00000000u},
-            {"0.222507385850720064199e-307", 0x000FFFFFFFFFFFFEu, 0x00000000u},
-            {"2.225073858507200642e-308", 0x000FFFFFFFFFFFFFu, 0x00000000u},
-            {"-2.22507385850720064199176395546e-308", 0x800FFFFFFFFFFFFEu, 0x80000000u},
-            {"222507385850720064199176395547e-337", 0x000FFFFFFFFFFFFFu, 0x00000000u},
-            {"-2.2250738585072011e-308", 0x800FFFFFFFFFFFFFu, 0x80000000u},
-            {"-22250738585072012e-324", 0x8010000000000000u, 0x80000000u},
-            {"-2225073858507201136e-326", 0x800FFFFFFFFFFFFFu, 0x80000000u},
-            {"0.2225073858507201137e-307", 0x0010000000000000u, 0x00000000u},
-            {"0.2225073858507201136e-307", 0x000FFFFFFFFFFFFFu, 0x00000000u},
-            {"-2.2250738585072011361e-308", 0x8010000000000000u, 0x80000000u},
-            {"2.22507385850720113605e-308", 0x000FFFFFFFFFFFFFu, 0x00000000u},
-            {"222507385850720113606e-328", 0x0010000000000000u, 0x00000000u},
-            {"22250738585072011360574097967e-336", 0x000FFFFFFFFFFFFFu, 0x00000000u},
-            {"0.222507385850720113605740979671e-307", 0x0010000000000000u, 0x00000000u},
-            {"22250738585072016e-324", 0x0010000000000000u, 0x00000000u},
-            {"0.22250738585072017e-307", 0x0010000000000001u, 0x00000000u},
-            {"0.222507385850720163e-307", 0x0010000000000000u, 0x00000000u},
-            {"2.225073858507201631e-308", 0x0010000000000001u, 0x00000000u},
-            {"-2.2250738585072016301e-308", 0x8010000000000000u, 0x80000000u},
-            {"22250738585072016302e-327", 0x0010000000000001u, 0x00000000u},
-            {"-222507385850720163012e-328", 0x8010000000000000u, 0x80000000u},
-            {"0.222507385850720163013e-307", 0x0010000000000001u, 0x00000000u},
-            {"0.222507385850720163012305563795e-307", 0x0010000000000000u, 0x00000000u},
-            {"-2.22507385850720163012305563796e-308", 0x8010000000000001u, 0x80000000u},
-            {"0.17976931348623156E+309", 0x7FEFFFFFFFFFFFFEu, 0x7F800000u},
-            {"1.7976931348623157e308", 0x7FEFFFFFFFFFFFFFu, 0x7F800000u},
-            {"1.797693134862315608e308", 0x7FEFFFFFFFFFFFFEu, 0x7F800000u},
-            {"-1797693134862315609e290", 0xFFEFFFFFFFFFFFFFu, 0xFF800000u},
-            {"-17976931348623156083e289", 0xFFEFFFFFFFFFFFFEu, 0xFF800000u},
-            {"-0.17976931348623156084E+309", 0xFFEFFFFFFFFFFFFFu, 0xFF800000u},
-            {"0.179769313486231560835E+309", 0x7FEFFFFFFFFFFFFEu, 0x7F800000u},
-            {"-1.79769313486231560836e308", 0xFFEFFFFFFFFFFFFFu, 0xFF800000u},
-            {"1.79769313486231560835325876058e308", 0x7FEFFFFFFFFFFFFEu, 0x7F800000u},
-            {"179769313486231560835325876059e279", 0x7FEFFFFFFFFFFFFFu, 0x7F800000u},
-            {"1.7976931348623158e308", 0x7FEFFFFFFFFFFFFFu, 0x7F800000u},
-            {"17976931348623159e292", 0x7FF0000000000000u, 0x7F800000u},
-            {"1797693134862315807e290", 0x7FEFFFFFFFFFFFFFu, 0x7F800000u},
-            {"0.1797693134862315808E+309", 0x7FF0000000000000u, 0x7F800000u},
-            {"0.17976931348623158079E+309", 0x7FEFFFFFFFFFFFFFu, 0x7F800000u},
-            {"-1.797693134862315808e308", 0xFFF0000000000000u, 0xFF800000u},
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-                "8189392089843750000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
-                "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
-                "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
-                "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
-                "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
-                "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
-                "00000000000000000000000000000000000000000000000000000000000000000e-37", 0x380FFFFFE0000000u, 0x00800000u
-            },
-            {
-                "1175494280757364291727882991035766513322858992758990427682963118425003064965173038558532425668090581"
-                "8939208984375000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
-                "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
-                "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
-                "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
-                "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
-                "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"
-                "00000000000001e-751", 0x380FFFFFE0000000u, 0x00800000u
-            },
-            {"0", 0x0000000000000000u, 0x00000000u},
-            {"-0", 0x8000000000000000u, 0x80000000u},
-            {"0.0", 0x0000000000000000u, 0x00000000u},
-            {"-0.0", 0x8000000000000000u, 0x80000000u},
-            {"0e999999999999999999999", 0x0000000000000000u, 0x00000000u},
-            {"-0.000e-99999", 0x8000000000000000u, 0x80000000u},
-            {"1e-400", 0x0000000000000000u, 0x00000000u},
-            {"-1e-400", 0x8000000000000000u, 0x80000000u},
-            {"1e400", 0x7FF0000000000000u, 0x7F800000u},
-            {"-1e400", 0xFFF0000000000000u, 0xFF800000u},
-            {"1e-50", 0x358DEE7A4AD4B81Fu, 0x00000000u},
-            {"-1e-50", 0xB58DEE7A4AD4B81Fu, 0x80000000u},
-            {"1e39", 0x48078287F49C4A1Du, 0x7F800000u},
-            {"-1e39", 0xC8078287F49C4A1Du, 0xFF800000u},
-            {"1e99999999999999999999999999", 0x7FF0000000000000u, 0x7F800000u},
-            {"1e-99999999999999999999999999", 0x0000000000000000u, 0x00000000u},
-            {"1e0000000000000000000000000000000000000000308", 0x7FE1CCF385EBC8A0u, 0x7F800000u},
-            {"123456789012345678901234567890e-30", 0x3FBF9ADD3746F65Fu, 0x3DFCD6EAu},
-            {"18446744073709551615", 0x43F0000000000000u, 0x5F800000u},
-            {"18446744073709551616", 0x43F0000000000000u, 0x5F800000u},
-            {"-9223372036854775808", 0xC3E0000000000000u, 0xDF000000u},
-            {"-9223372036854775809", 0xC3E0000000000000u, 0xDF000000u},
-        }
-    };
-    return table;
-}
-
-} // namespace float_hard_cases

tests/src/unit-binary_utf8_error_handler.cpp

@@ -0,0 +1,346 @@
+//     __ _____ _____ _____
+//  __|  |   __|     |   | |  JSON for Modern C++ (supporting code)
+// |  |  |__   |  |  | | | |  version 3.12.0
+// |_____|_____|_____|_|___|  https://github.com/nlohmann/json
+//
+// SPDX-FileCopyrightText: 2013-2026 Niels Lohmann <https://nlohmann.me>
+// SPDX-License-Identifier: MIT
+
+#include "doctest_compatibility.h"
+
+#include <nlohmann/json.hpp>
+using nlohmann::json;
+
+#include <string>
+#include <vector>
+
+namespace
+{
+
+struct ill_formed_case
+{
+    const char* name;
+    std::string bytes;
+};
+
+// RFC 3629 ill-formed sequences used throughout this file, plus one
+// well-formed sequence for contrast
+const std::vector<ill_formed_case> ill_formed_cases =
+{
+    {"overlong", "\xC0\xAE"},
+    {"lone_0xFF", "\xFF"},
+    {"truncated", "\xE2\x82"},
+    {"surrogate", "\xED\xA0\x80"},
+};
+
+const std::string valid_sequence = "\xC3\xA9"; // U+00E9, "é"
+
+using eh = json::error_handler_t;
+const std::vector<eh> all_handlers = {eh::strict, eh::replace, eh::ignore, eh::keep};
+
+// what dump()+parse() produces for a sanitizing error_handler; this is the
+// ground truth every binary writer/reader is checked against
+std::string dump_and_parse(const std::string& raw, eh error_handler)
+{
+    return json::parse(json(raw).dump(-1, ' ', false, error_handler)).get<std::string>();
+}
+
+} // namespace
+
+TEST_CASE("UTF-8 error_handler for the binary readers and writers")
+{
+    SECTION("writers: string value")
+    {
+        for (const auto& c : ill_formed_cases)
+        {
+            CAPTURE(c.name);
+            const json jval = c.bytes;
+
+            CHECK_THROWS_AS(json::to_cbor(jval, eh::strict), json::type_error&);
+            CHECK_THROWS_AS(json::to_ubjson(jval, false, false, eh::strict), json::type_error&);
+            CHECK_THROWS_AS(json::to_bjdata(jval, false, false, json::bjdata_version_t::draft2, eh::strict), json::type_error&);
+            {
+                json jobj;
+                jobj["k"] = jval;
+                CHECK_THROWS_AS(json::to_bson(jobj, eh::strict), json::type_error&);
+            }
+
+            for (const auto h :
+                    {
+                        eh::replace, eh::ignore
+                    })
+            {
+                CAPTURE(static_cast<int>(h));
+                const std::string expected = dump_and_parse(c.bytes, h);
+
+                CHECK(json::from_cbor(json::to_cbor(jval, h)).get<std::string>() == expected);
+                CHECK(json::from_ubjson(json::to_ubjson(jval, false, false, h)).get<std::string>() == expected);
+                CHECK(json::from_bjdata(json::to_bjdata(jval, false, false, json::bjdata_version_t::draft2, h)).get<std::string>() == expected);
+                {
+                    json jobj;
+                    jobj["k"] = jval;
+                    const auto bytes = json::to_bson(jobj, h);
+                    CHECK(json::from_bson(bytes)["k"].get<std::string>() == expected);
+                }
+            }
+
+            // keep: the writer passes the ill-formed bytes through unchanged,
+            // exactly as every binary writer did before this parameter existed
+            CHECK(json::from_cbor(json::to_cbor(jval, eh::keep)).get<std::string>() == c.bytes);
+            CHECK(json::from_ubjson(json::to_ubjson(jval, false, false, eh::keep)).get<std::string>() == c.bytes);
+            CHECK(json::from_bjdata(json::to_bjdata(jval, false, false, json::bjdata_version_t::draft2, eh::keep)).get<std::string>() == c.bytes);
+            {
+                json jobj;
+                jobj["k"] = jval;
+                const auto bytes = json::to_bson(jobj, eh::keep);
+                CHECK(json::from_bson(bytes)["k"].get<std::string>() == c.bytes);
+            }
+        }
+    }
+
+    SECTION("writers: object key")
+    {
+        for (const auto& c : ill_formed_cases)
+        {
+            CAPTURE(c.name);
+            json jobj;
+            jobj[c.bytes] = 1;
+
+            CHECK_THROWS_AS(json::to_cbor(jobj, eh::strict), json::type_error&);
+            CHECK_THROWS_AS(json::to_ubjson(jobj, false, false, eh::strict), json::type_error&);
+            CHECK_THROWS_AS(json::to_bjdata(jobj, false, false, json::bjdata_version_t::draft2, eh::strict), json::type_error&);
+            CHECK_THROWS_AS(json::to_bson(jobj, eh::strict), json::type_error&);
+
+            for (const auto h :
+                    {
+                        eh::replace, eh::ignore
+                    })
+            {
+                CAPTURE(static_cast<int>(h));
+                const std::string expected = dump_and_parse(c.bytes, h);
+
+                CHECK(json::from_cbor(json::to_cbor(jobj, h)).begin().key() == expected);
+                CHECK(json::from_ubjson(json::to_ubjson(jobj, false, false, h)).begin().key() == expected);
+                CHECK(json::from_bjdata(json::to_bjdata(jobj, false, false, json::bjdata_version_t::draft2, h)).begin().key() == expected);
+                CHECK(json::from_bson(json::to_bson(jobj, h)).begin().key() == expected);
+            }
+
+            // keep: object keys round-trip unchanged too
+            CHECK(json::from_cbor(json::to_cbor(jobj, eh::keep)).begin().key() == c.bytes);
+            CHECK(json::from_ubjson(json::to_ubjson(jobj, false, false, eh::keep)).begin().key() == c.bytes);
+            CHECK(json::from_bjdata(json::to_bjdata(jobj, false, false, json::bjdata_version_t::draft2, eh::keep)).begin().key() == c.bytes);
+            CHECK(json::from_bson(json::to_bson(jobj, eh::keep)).begin().key() == c.bytes);
+        }
+    }
+
+    SECTION("readers: string value")
+    {
+        for (const auto& c : ill_formed_cases)
+        {
+            CAPTURE(c.name);
+
+            // bytes produced the lenient (keep) way, as any binary reader
+            // accepted them before this parameter existed
+            const auto cbor_bytes = json::to_cbor(json(c.bytes), eh::keep);
+            const auto msgpack_bytes = json::to_msgpack(json(c.bytes)); // to_msgpack has no error_handler; always pass-through
+            const auto ubjson_bytes = json::to_ubjson(json(c.bytes), false, false, eh::keep);
+            const auto bjdata_bytes = json::to_bjdata(json(c.bytes), false, false, json::bjdata_version_t::draft2, eh::keep);
+            const auto bson_bytes = [&c]
+            {
+                json jobj;
+                jobj["k"] = c.bytes;
+                return json::to_bson(jobj, eh::keep);
+            }();
+
+            // keep (the default): bytes are kept unchanged
+            CHECK(json::from_cbor(cbor_bytes).get<std::string>() == c.bytes);
+            CHECK(json::from_msgpack(msgpack_bytes).get<std::string>() == c.bytes);
+            CHECK(json::from_ubjson(ubjson_bytes).get<std::string>() == c.bytes);
+            CHECK(json::from_bjdata(bjdata_bytes).get<std::string>() == c.bytes);
+            CHECK(json::from_bson(bson_bytes)["k"].get<std::string>() == c.bytes);
+
+            // strict: parse_error.113, discarded (not thrown) when allow_exceptions is false
+            CHECK_THROWS_AS(json::from_cbor(cbor_bytes, true, true, json::cbor_tag_handler_t::error, eh::strict), json::parse_error&);
+            CHECK(json::from_cbor(cbor_bytes, true, false, json::cbor_tag_handler_t::error, eh::strict).is_discarded());
+            CHECK_THROWS_AS(json::from_msgpack(msgpack_bytes, true, true, eh::strict), json::parse_error&);
+            CHECK(json::from_msgpack(msgpack_bytes, true, false, eh::strict).is_discarded());
+            CHECK_THROWS_AS(json::from_ubjson(ubjson_bytes, true, true, eh::strict), json::parse_error&);
+            CHECK(json::from_ubjson(ubjson_bytes, true, false, eh::strict).is_discarded());
+            CHECK_THROWS_AS(json::from_bjdata(bjdata_bytes, true, true, eh::strict), json::parse_error&);
+            CHECK(json::from_bjdata(bjdata_bytes, true, false, eh::strict).is_discarded());
+            CHECK_THROWS_AS(json::from_bson(bson_bytes, true, true, eh::strict), json::parse_error&);
+            CHECK(json::from_bson(bson_bytes, true, false, eh::strict).is_discarded());
+
+            // replace / ignore: match what dump() would have sanitized the same bytes to
+            for (const auto h :
+                    {
+                        eh::replace, eh::ignore
+                    })
+            {
+                CAPTURE(static_cast<int>(h));
+                const std::string expected = dump_and_parse(c.bytes, h);
+
+                CHECK(json::from_cbor(cbor_bytes, true, true, json::cbor_tag_handler_t::error, h).get<std::string>() == expected);
+                CHECK(json::from_msgpack(msgpack_bytes, true, true, h).get<std::string>() == expected);
+                CHECK(json::from_ubjson(ubjson_bytes, true, true, h).get<std::string>() == expected);
+                CHECK(json::from_bjdata(bjdata_bytes, true, true, h).get<std::string>() == expected);
+                CHECK(json::from_bson(bson_bytes, true, true, h)["k"].get<std::string>() == expected);
+            }
+        }
+    }
+
+    SECTION("readers: object key")
+    {
+        for (const auto& c : ill_formed_cases)
+        {
+            CAPTURE(c.name);
+
+            json jobj;
+            jobj[c.bytes] = 1;
+            const auto cbor_bytes = json::to_cbor(jobj, eh::keep);
+            const auto msgpack_bytes = json::to_msgpack(jobj);
+            const auto ubjson_bytes = json::to_ubjson(jobj, false, false, eh::keep);
+            const auto bjdata_bytes = json::to_bjdata(jobj, false, false, json::bjdata_version_t::draft2, eh::keep);
+            const auto bson_bytes = json::to_bson(jobj, eh::keep);
+
+            CHECK(json::from_cbor(cbor_bytes).begin().key() == c.bytes);
+            CHECK(json::from_msgpack(msgpack_bytes).begin().key() == c.bytes);
+            CHECK(json::from_ubjson(ubjson_bytes).begin().key() == c.bytes);
+            CHECK(json::from_bjdata(bjdata_bytes).begin().key() == c.bytes);
+            CHECK(json::from_bson(bson_bytes).begin().key() == c.bytes);
+
+            CHECK_THROWS_AS(json::from_cbor(cbor_bytes, true, true, json::cbor_tag_handler_t::error, eh::strict), json::parse_error&);
+            CHECK_THROWS_AS(json::from_msgpack(msgpack_bytes, true, true, eh::strict), json::parse_error&);
+            CHECK_THROWS_AS(json::from_ubjson(ubjson_bytes, true, true, eh::strict), json::parse_error&);
+            CHECK_THROWS_AS(json::from_bjdata(bjdata_bytes, true, true, eh::strict), json::parse_error&);
+            CHECK_THROWS_AS(json::from_bson(bson_bytes, true, true, eh::strict), json::parse_error&);
+
+            for (const auto h :
+                    {
+                        eh::replace, eh::ignore
+                    })
+            {
+                CAPTURE(static_cast<int>(h));
+                const std::string expected = dump_and_parse(c.bytes, h);
+
+                CHECK(json::from_cbor(cbor_bytes, true, true, json::cbor_tag_handler_t::error, h).begin().key() == expected);
+                CHECK(json::from_msgpack(msgpack_bytes, true, true, h).begin().key() == expected);
+                CHECK(json::from_ubjson(ubjson_bytes, true, true, h).begin().key() == expected);
+                CHECK(json::from_bjdata(bjdata_bytes, true, true, h).begin().key() == expected);
+                CHECK(json::from_bson(bson_bytes, true, true, h).begin().key() == expected);
+            }
+        }
+    }
+
+    SECTION("well-formed UTF-8 is unaffected by error_handler")
+    {
+        const json jval = valid_sequence;
+        json jobj;
+        jobj[valid_sequence] = valid_sequence;
+
+        for (const auto h : all_handlers)
+        {
+            CAPTURE(static_cast<int>(h));
+
+            CHECK(json::from_cbor(json::to_cbor(jval, h)).get<std::string>() == valid_sequence);
+            CHECK(json::from_ubjson(json::to_ubjson(jval, false, false, h)).get<std::string>() == valid_sequence);
+            CHECK(json::from_bjdata(json::to_bjdata(jval, false, false, json::bjdata_version_t::draft2, h)).get<std::string>() == valid_sequence);
+            CHECK(json::from_bson(json::to_bson(jobj, h)).begin().key() == valid_sequence);
+
+            CHECK(json::from_cbor(json::to_cbor(jval, eh::keep), true, true, json::cbor_tag_handler_t::error, h).get<std::string>() == valid_sequence);
+            CHECK(json::from_msgpack(json::to_msgpack(jval), true, true, h).get<std::string>() == valid_sequence);
+        }
+    }
+
+    SECTION("dump() with error_handler_t::keep writes raw bytes as is")
+    {
+        for (const auto& c : ill_formed_cases)
+        {
+            CAPTURE(c.name);
+
+            const json jval = c.bytes;
+            const std::string dumped = jval.dump(-1, ' ', false, eh::keep);
+            CHECK(dumped.find(c.bytes) != std::string::npos);
+
+            // even with ensure_ascii, the ill-formed bytes are written as is
+            const std::string dumped_ascii = jval.dump(-1, ' ', true, eh::keep);
+            CHECK(dumped_ascii.find(c.bytes) != std::string::npos);
+        }
+
+        // well-formed characters around an ill-formed sequence are still
+        // escaped as usual under ensure_ascii
+        const json mixed = valid_sequence + ill_formed_cases[1].bytes; // "é" + lone 0xFF
+        const std::string dumped_mixed = mixed.dump(-1, ' ', true, eh::keep);
+        CHECK(dumped_mixed.find("\\u00e9") != std::string::npos);
+        CHECK(dumped_mixed.find(ill_formed_cases[1].bytes) != std::string::npos);
+
+        // the byte that ends an ill-formed sequence is read again, so a quote,
+        // a backslash, or a control character after it is still escaped, and
+        // a well-formed code point after it is escaped under ensure_ascii
+        for (const bool ensure_ascii :
+                {
+                    false, true
+                })
+        {
+            CAPTURE(ensure_ascii);
+            CHECK(json("\xC3\"").dump(-1, ' ', ensure_ascii, eh::keep) == "\"\xC3\\\"\"");
+            CHECK(json("\xC3\\").dump(-1, ' ', ensure_ascii, eh::keep) == "\"\xC3\\\\\"");
+            CHECK(json("\xC3\n").dump(-1, ' ', ensure_ascii, eh::keep) == "\"\xC3\\n\"");
+            CHECK(json("\xE2\x82\"").dump(-1, ' ', ensure_ascii, eh::keep) == "\"\xE2\x82\\\"\"");
+            CHECK(json("\xFF\"").dump(-1, ' ', ensure_ascii, eh::keep) == "\"\xFF\\\"\"");
+            CHECK(json("a\xE2\x82").dump(-1, ' ', ensure_ascii, eh::keep) == "\"a\xE2\x82\"");
+        }
+        CHECK(json("\xC3\xC3\xA9").dump(-1, ' ', false, eh::keep) == "\"\xC3\xC3\xA9\"");
+        CHECK(json("\xC3\xC3\xA9").dump(-1, ' ', true, eh::keep) == "\"\xC3\\u00e9\"");
+    }
+
+    SECTION("to_msgpack and to_bon8 are not affected by error_handler")
+    {
+        const json jval = ill_formed_cases[1].bytes; // lone 0xFF
+
+        // to_msgpack has no error_handler parameter; the bytes are always
+        // passed through, as MessagePack's spec allows
+        CHECK(json::from_msgpack(json::to_msgpack(jval)).get<std::string>() == ill_formed_cases[1].bytes);
+
+        // to_bon8 has no error_handler parameter either; UTF-8 is structural
+        // for BON8, so it always rejects ill-formed input
+        CHECK_THROWS_AS(json::to_bon8(jval), json::type_error&);
+    }
+
+    SECTION("allow_exceptions=false with error_handler_t::strict discards the value")
+    {
+        const auto bytes = json::to_cbor(json(ill_formed_cases[0].bytes), eh::keep);
+        const json result = json::from_cbor(bytes, true, false, json::cbor_tag_handler_t::error, eh::strict);
+        CHECK(result.is_discarded());
+    }
+
+    SECTION("default parameters are unchanged")
+    {
+        const json jval = ill_formed_cases[0].bytes;
+
+        // to_*: the default error_handler is strict, so ill-formed input still throws
+        CHECK_THROWS_AS(json::to_cbor(jval), json::type_error&);
+        CHECK_THROWS_AS(json::to_ubjson(jval), json::type_error&);
+        CHECK_THROWS_AS(json::to_bjdata(jval), json::type_error&);
+        {
+            json jobj;
+            jobj["k"] = jval;
+            CHECK_THROWS_AS(json::to_bson(jobj), json::type_error&);
+        }
+
+        // from_*: the default error_handler is keep, so ill-formed bytes are
+        // still accepted unchanged, exactly as in release 3.12.0
+        const auto cbor_bytes = json::to_cbor(jval, eh::keep);
+        CHECK(json::from_cbor(cbor_bytes).get<std::string>() == ill_formed_cases[0].bytes);
+        const auto ubjson_bytes = json::to_ubjson(jval, false, false, eh::keep);
+        CHECK(json::from_ubjson(ubjson_bytes).get<std::string>() == ill_formed_cases[0].bytes);
+        const auto bjdata_bytes = json::to_bjdata(jval, false, false, json::bjdata_version_t::draft2, eh::keep);
+        CHECK(json::from_bjdata(bjdata_bytes).get<std::string>() == ill_formed_cases[0].bytes);
+        const auto msgpack_bytes = json::to_msgpack(jval);
+        CHECK(json::from_msgpack(msgpack_bytes).get<std::string>() == ill_formed_cases[0].bytes);
+        json bson_obj;
+        bson_obj["k"] = jval;
+        const auto bson_bytes = json::to_bson(bson_obj, eh::keep);
+        CHECK(json::from_bson(bson_bytes)["k"].get<std::string>() == ill_formed_cases[0].bytes);
+    }
+}

tests/src/unit-bjdata.cpp

@@ -3907,6 +3907,41 @@ TEST_CASE("Universal Binary JSON Specification Examples 1")
             CHECK(json::to_bjdata(j) == v);
             CHECK(json::from_bjdata(v) == j);
         }
+
+        SECTION("ill-formed UTF-8 (see #5529, #5651)")
+        {
+            // none of the binary format specs requires a decoder to reject
+            // ill-formed UTF-8 in a text string, so a value whose bytes are
+            // not valid UTF-8 (0xC0 0xAE is an overlong encoding of '.')
+            // round-trips byte for byte as a string value; to_bjdata() is
+            // strict, so such a value cannot be written back
+            const std::vector<uint8_t> v = {'S', 'i', 2, 0xc0, 0xae};
+            json j;
+            CHECK_NOTHROW(j = json::from_bjdata(v));
+            REQUIRE(j.is_string());
+            CHECK(j.get_ref<const json::string_t&>() == std::string("\xc0\xae"));
+            CHECK_THROWS_AS(j.dump(), json::type_error&);
+            CHECK_THROWS_AS(json::to_bjdata(j), json::type_error&);
+
+            // the same bytes as an object key round-trip as well
+            const std::vector<uint8_t> v_key = {'{', 'i', 2, 0xc0, 0xae, 'i', 1, '}'};
+            json j_key;
+            CHECK_NOTHROW(j_key = json::from_bjdata(v_key));
+            REQUIRE(j_key.is_object());
+            CHECK(j_key.contains(std::string("\xc0\xae")));
+            CHECK_THROWS_AS(json::to_bjdata(j_key), json::type_error&);
+
+            CHECK_THROWS_WITH_AS(json::to_bjdata(json("\xFF")), "[json.exception.type_error.316] invalid UTF-8 byte at index 0: 0xFF", json::type_error&);
+            // a truncated multi-byte sequence
+            CHECK_THROWS_WITH_AS(json::to_bjdata(json("\xC3")), "[json.exception.type_error.316] invalid UTF-8 byte at index 0: 0xC3", json::type_error&);
+            // an encoded surrogate half (U+D800)
+            CHECK_THROWS_WITH_AS(json::to_bjdata(json("\xED\xA0\x80")), "[json.exception.type_error.316] invalid UTF-8 byte at index 0: 0xED", json::type_error&);
+            // an overlong encoding of '.'
+            CHECK_THROWS_WITH_AS(json::to_bjdata(json("\xC0\xAF")), "[json.exception.type_error.316] invalid UTF-8 byte at index 0: 0xC0", json::type_error&);
+
+            // an object key with ill-formed UTF-8 is rejected the same way
+            CHECK_THROWS_WITH_AS(json::to_bjdata(json{{"\xFF", 1}}), "[json.exception.type_error.316] invalid UTF-8 byte at index 0: 0xFF", json::type_error&);
+        }
     }
 
     SECTION("Array Type")

tests/src/unit-bson.cpp

@@ -154,6 +154,51 @@ TEST_CASE("BSON")
 #endif
     }
 
+    SECTION("ill-formed UTF-8 (see #5529, #5651)")
+    {
+        // a BSON document {"s": "\xC0\xAE"} (0xC0 0xAE is an overlong
+        // encoding of '.'); the BSON spec does not require a decoder to
+        // reject ill-formed UTF-8 in a string value, so the reader hands the
+        // bytes back unchanged
+        const std::vector<uint8_t> v =
+        {
+            0x0F, 0x00, 0x00, 0x00, // document length
+            0x02, 's', 0x00,        // type 0x02 (string), key "s"
+            0x03, 0x00, 0x00, 0x00, // string length (including null)
+            0xc0, 0xae, 0x00,       // string content and its null terminator
+            0x00                    // document terminator
+        };
+        json j;
+        CHECK_NOTHROW(j = json::from_bson(v));
+        REQUIRE(j.is_object());
+        REQUIRE(j.contains("s"));
+        CHECK(j["s"].get_ref<const json::string_t&>() == std::string("\xc0\xae"));
+        // dump() still requires valid UTF-8 and throws for such a value
+        CHECK_THROWS_AS(j.dump(), json::type_error&);
+        // to_bson() is strict as well, so the value cannot be written back
+        CHECK_THROWS_AS(json::to_bson(j), json::type_error&);
+
+        // to_bson() rejects the same kind of ill-formed string value, before
+        // any bytes reach the output adapter (the BSON document length
+        // prefix must be known up front, so nothing is written incrementally)
+        std::vector<std::uint8_t> out{0x42}; // a sentinel byte the writer must not touch
+        CHECK_THROWS_WITH_AS(json::to_bson(json{{"s", "\xFF"}}, nlohmann::detail::output_adapter<std::uint8_t>(out)), "[json.exception.type_error.316] invalid UTF-8 byte at index 0: 0xFF", json::type_error&);
+        CHECK(out == std::vector<std::uint8_t> {0x42});
+
+        CHECK_THROWS_WITH_AS(json::to_bson(json{{"s", "\xFF"}}), "[json.exception.type_error.316] invalid UTF-8 byte at index 0: 0xFF", json::type_error&);
+        // a truncated multi-byte sequence
+        CHECK_THROWS_WITH_AS(json::to_bson(json{{"s", "\xC3"}}), "[json.exception.type_error.316] invalid UTF-8 byte at index 0: 0xC3", json::type_error&);
+        // an encoded surrogate half (U+D800)
+        CHECK_THROWS_WITH_AS(json::to_bson(json{{"s", "\xED\xA0\x80"}}), "[json.exception.type_error.316] invalid UTF-8 byte at index 0: 0xED", json::type_error&);
+        // an overlong encoding of '.'
+        CHECK_THROWS_WITH_AS(json::to_bson(json{{"s", "\xC0\xAF"}}), "[json.exception.type_error.316] invalid UTF-8 byte at index 0: 0xC0", json::type_error&);
+
+        // an object key with ill-formed UTF-8 is rejected as well; unlike
+        // the reader (which never validates element names), the writer
+        // checks both string values and object keys
+        CHECK_THROWS_WITH_AS(json::to_bson(json{{"\xFF", 1}}), "[json.exception.type_error.316] invalid UTF-8 byte at index 0: 0xFF", json::type_error&);
+    }
+
     SECTION("lengths exceeding INT32_MAX cannot be serialized to BSON")
     {
         // out_of_range.412 is thrown from a single shared helper

tests/src/unit-cbor.cpp

@@ -1801,19 +1801,40 @@ TEST_CASE("CBOR")
             CHECK_THROWS_WITH_AS(_ = json::from_cbor(std::vector<uint8_t>({0xA1, 0x7C, 0x01})), "[json.exception.parse_error.113] parse error at byte 2: syntax error while parsing CBOR string: expected length specification (0x60-0x7B) or indefinite string type (0x7F); last byte: 0x7C", json::parse_error&);
         }
 
-        SECTION("invalid UTF-8 in string (see #5529)")
+        SECTION("ill-formed UTF-8 in string (see #5529, #5651)")
         {
+            // RFC 8949 §3.1 leaves it up to the decoder whether to reject
+            // ill-formed UTF-8 in a text string; this library does not, and
+            // hands the original bytes back unchanged, matching the
+            // MessagePack reader and the behavior before #5185/#5531 (not in
+            // any release)
+
             // a two-character text string (major type 3) whose bytes are not
-            // valid UTF-8 (0xC0 0xAE is an overlong encoding of '.') must be
-            // rejected at decode time, matching every other kind of
-            // malformed binary input, rather than only failing later when
-            // the resulting value is dumped
-            json _;
-            CHECK_THROWS_WITH_AS(_ = json::from_cbor(std::vector<uint8_t>({0x62, 0xc0, 0xae})), "[json.exception.parse_error.113] parse error at byte 3: syntax error while parsing CBOR string: invalid string: ill-formed UTF-8 byte", json::parse_error&);
-            CHECK(json::from_cbor(std::vector<uint8_t>({0x62, 0xc0, 0xae}), true, false).is_discarded());
+            // valid UTF-8 (0xC0 0xAE is an overlong encoding of '.') round-trips
+            // byte for byte as a string value
+            const std::vector<uint8_t> ill_formed_value = {0x62, 0xc0, 0xae};
+            json j_value;
+            CHECK_NOTHROW(j_value = json::from_cbor(ill_formed_value));
+            REQUIRE(j_value.is_string());
+            CHECK(j_value.get_ref<const json::string_t&>() == std::string("\xc0\xae"));
+            // dump() still requires valid UTF-8 and throws for such a value,
+            // unless an error handler that replaces or ignores the bytes is
+            // passed
+            CHECK_THROWS_AS(j_value.dump(), json::type_error&);
+            // to_cbor() is strict as well, so the value cannot be written back
+            CHECK_THROWS_AS(json::to_cbor(j_value), json::type_error&);
+
+            // the same bytes as an object key round-trip as well
+            const std::vector<uint8_t> ill_formed_key = {0xa1, 0x62, 0xc0, 0xae, 0x01};
+            json j_key;
+            CHECK_NOTHROW(j_key = json::from_cbor(ill_formed_key));
+            REQUIRE(j_key.is_object());
+            CHECK(j_key.contains(std::string("\xc0\xae")));
+            CHECK_THROWS_AS(json::to_cbor(j_key), json::type_error&);
 
             // a CBOR byte string (major type 2) with the very same bytes is
             // NOT text and must still be accepted as-is
+            json _;
             CHECK_NOTHROW(_ = json::from_cbor(std::vector<uint8_t>({0x42, 0xc0, 0xae})));
             CHECK(_ == json::binary(std::vector<std::uint8_t>({0xc0, 0xae})));
 
@@ -1822,17 +1843,46 @@ TEST_CASE("CBOR")
             CHECK(json::from_cbor(json::to_cbor(j)) == j);
         }
 
-        SECTION("invalid UTF-8 in indefinite-length string")
+        SECTION("to_cbor rejects ill-formed UTF-8 (see #5651)")
+        {
+            // to_cbor() must reject the same ill-formed strings from_cbor()
+            // rejects, so a value it accepts can always be read back
+            CHECK_THROWS_WITH_AS(json::to_cbor(json("\xFF")), "[json.exception.type_error.316] invalid UTF-8 byte at index 0: 0xFF", json::type_error&);
+            // a truncated multi-byte sequence
+            CHECK_THROWS_WITH_AS(json::to_cbor(json("\xC3")), "[json.exception.type_error.316] invalid UTF-8 byte at index 0: 0xC3", json::type_error&);
+            // an encoded surrogate half (U+D800)
+            CHECK_THROWS_WITH_AS(json::to_cbor(json("\xED\xA0\x80")), "[json.exception.type_error.316] invalid UTF-8 byte at index 0: 0xED", json::type_error&);
+            // an overlong encoding of '.'
+            CHECK_THROWS_WITH_AS(json::to_cbor(json("\xC0\xAF")), "[json.exception.type_error.316] invalid UTF-8 byte at index 0: 0xC0", json::type_error&);
+
+            // an object key with ill-formed UTF-8 is rejected the same way
+            CHECK_THROWS_WITH_AS(json::to_cbor(json{{"\xFF", 1}}), "[json.exception.type_error.316] invalid UTF-8 byte at index 0: 0xFF", json::type_error&);
+
+            // binary values are not text and are unaffected
+            CHECK_NOTHROW(json::to_cbor(json::binary(std::vector<std::uint8_t>({0xFF}))));
+        }
+
+        SECTION("ill-formed UTF-8 in indefinite-length string")
         {
             json _;
 
-            // every chunk must be valid UTF-8 on its own (RFC 8949, Section
-            // 3.2.3), so a code point split across two chunks is rejected
-            CHECK_THROWS_WITH_AS(_ = json::from_cbor(std::vector<uint8_t>({0x7f, 0x61, 0xc3, 0x61, 0xa9, 0xff})), "[json.exception.parse_error.113] parse error at byte 3: syntax error while parsing CBOR string: invalid string: ill-formed UTF-8 byte", json::parse_error&);
-            CHECK(json::from_cbor(std::vector<uint8_t>({0x7f, 0x61, 0xc3, 0x61, 0xa9, 0xff}), true, false).is_discarded());
+            // the chunks are concatenated as is, without checking that each
+            // chunk is valid UTF-8 on its own (RFC 8949, Section 3.2.3), so
+            // a code point split across two chunks yields a valid string
+            CHECK_NOTHROW(_ = json::from_cbor(std::vector<uint8_t>({0x7f, 0x61, 0xc3, 0x61, 0xa9, 0xff})));
+            CHECK(_ == "\xc3\xa9");
+            CHECK(_.dump() == "\"\xc3\xa9\"");
 
-            // an ill-formed later chunk is rejected after valid ones
-            CHECK_THROWS_WITH_AS(_ = json::from_cbor(std::vector<uint8_t>({0x7f, 0x62, 0xc3, 0xa9, 0x62, 0xc0, 0xae, 0xff})), "[json.exception.parse_error.113] parse error at byte 7: syntax error while parsing CBOR string: invalid string: ill-formed UTF-8 byte", json::parse_error&);
+            // a truncated code point is kept as is
+            CHECK_NOTHROW(_ = json::from_cbor(std::vector<uint8_t>({0x7f, 0x61, 0xc3, 0xff})));
+            CHECK(_ == "\xc3");
+            CHECK_THROWS_AS(_.dump(), json::type_error&);
+            CHECK_THROWS_AS(json::to_cbor(_), json::type_error&);
+
+            // an ill-formed later chunk is kept after valid ones
+            CHECK_NOTHROW(_ = json::from_cbor(std::vector<uint8_t>({0x7f, 0x62, 0xc3, 0xa9, 0x62, 0xc0, 0xae, 0xff})));
+            CHECK(_ == "\xc3\xa9\xc0\xae");
+            CHECK_THROWS_AS(_.dump(), json::type_error&);
 
             // valid multi-byte chunks are accepted
             CHECK(json::from_cbor(std::vector<uint8_t>({0x7f, 0x62, 0xc3, 0xa9, 0x62, 0xc3, 0xb6, 0xff})) == "\xc3\xa9\xc3\xb6");
@@ -1840,9 +1890,6 @@ TEST_CASE("CBOR")
 
         SECTION("many chunks in indefinite-length string")
         {
-            // only the newly read chunk is validated, not the whole string
-            // collected so far; validating the latter made this input take
-            // quadratic time (about ten seconds for 100000 chunks)
             constexpr std::size_t chunks = 100000;
             std::vector<uint8_t> v{0x7f};
             for (std::size_t i = 0; i < chunks; ++i)

tests/src/unit-class_lexer.cpp

@@ -13,18 +13,15 @@
 using nlohmann::json;
 
 #include <array> // array
+#include <cfloat> // FLT_EVAL_METHOD
 #include <cstdint> // uint32_t, uint64_t
-#include <cstdio> // snprintf
 #include <cstdlib> // strtod
 #include <cstring> // memcpy
-#include <map> // map
 #include <sstream> // stringstream
 #include <string> // string
 #include <utility> // pair
 #include <vector> // vector
 
-#include "float_hard_cases.hpp"
-
 namespace
 {
 // shortcut to scan a string literal
@@ -260,7 +257,7 @@ TEST_CASE("lexer number fast path")
             "123456789012345678901234567890",  // huge -> float
             "0.30000000000000004", "2.2250738585072014e-308", "1e308",
             // high-precision / wide-exponent values that exercise the
-            // Eisel-Lemire path beyond the Clinger subset
+            // std::from_chars (Eisel-Lemire) path beyond the Clinger subset
             "1.7976931348623157e308", "1.2345678901234567e-250",
             "9007199254740993", "5e-324", "1e-320"
         };
@@ -282,18 +279,20 @@ TEST_CASE("lexer number fast path")
         }
     }
 
-    SECTION("significant digits around Clinger's fast path")
+    SECTION("significant-digit gate for the Clinger fast path")
     {
-        // Clinger's fast path needs a significand of at most 2^53, which
-        // tokens with 17 or more significant digits exceed. The conversion
-        // splits the token at the positions the scanners recorded, so leading
-        // zeros must not count as digits - "0.1234567890123456" has 16
-        // significant digits, not 17 - and both scanners must agree.
+        // Clinger's fast path needs a significand below 2^53, so it cannot
+        // succeed once the mantissa has 17 or more significant digits (the
+        // significand would be at least 10^16). The lexer skips the attempt
+        // there. That is only allowed to save work: every value must still come
+        // out bit-exactly, and both scanners must agree. In particular the gate
+        // must not fire for tokens whose leading zeros merely look like extra
+        // digits - "0.1234567890123456" has 16 significant digits, not 17.
         const std::vector<std::string> numbers =
         {
             "1234567890123456",                  // 16 significant digits
-            "12345678901234567",                 // 17
-            "123456789012345678",                // 18
+            "12345678901234567",                 // 17 -> attempt skipped
+            "123456789012345678",                // 18 -> attempt skipped
             "0.1234567890123456",                // 16: the leading "0" is not significant
             "0.12345678901234567",               // 17
             "0.00000000000000001",               // 1, in a long token
@@ -664,145 +663,46 @@ TEST_CASE("lexer string fast path")
     }
 }
 
-namespace
+TEST_CASE("parse_float_fast declines what it cannot convert exactly")
 {
-// the index of the decimal point (or npos) and of the end of the mantissa of a
-// number token, which the lexer records while scanning it
-std::pair<std::size_t, std::size_t> float_token_layout(const std::string& s)
-{
-    std::size_t dot = std::string::npos;
-    std::size_t mantissa_end = s.size();
-    for (std::size_t i = 0; i < s.size(); ++i)
+    // The lexer only hands well-formed numbers to parse_float_fast, so the
+    // malformed ones below can only be passed to it directly. Declining is
+    // always safe: the caller then falls back to a slower, exact conversion.
+    const auto fast = [](const std::string & s, double & out)
     {
-        if (s[i] == '.')
-        {
-            dot = i;
-        }
-        else if (s[i] == 'e' || s[i] == 'E')
-        {
-            mantissa_end = i;
-            break;
-        }
-    }
-    return {dot, mantissa_end};
-}
+        return nlohmann::detail::parse_float_fast(s.data(), s.data() + s.size(), out);
+    };
+    double out = 0;
 
-template<typename FloatType>
-FloatType parse_native(const std::string& s)
-{
-    const auto layout = float_token_layout(s);
-    return nlohmann::detail::parse_float_native<FloatType>(s.data(), s.data() + s.size(), layout.first, layout.second);
-}
+#if defined(FLT_EVAL_METHOD) && FLT_EVAL_METHOD != 0
+    // without true double precision, the fast path declines everything
+    CHECK_FALSE(fast("1.5", out));
+#else
+    CHECK(fast("1.5", out));
+    CHECK(out == 1.5);
+    CHECK(fast("+2.5e1", out));
+    CHECK(out == 25.0);
+    CHECK(fast("-25E-1", out));
+    CHECK(out == -2.5);
+    CHECK(fast("1e", out));
+    CHECK(out == 1.0);
+#endif
 
-std::uint64_t bits_of(double d)
-{
-    std::uint64_t b = 0;
-    std::memcpy(&b, &d, sizeof(b));
-    return b;
-}
+    // not a number
+    CHECK_FALSE(fast("", out));
+    CHECK_FALSE(fast("-", out));
+    CHECK_FALSE(fast(".", out));
+    CHECK_FALSE(fast("1.2.3", out));
+    CHECK_FALSE(fast("1x", out));
+    CHECK_FALSE(fast("1e+", out));
+    CHECK_FALSE(fast("1e1x", out));
 
-std::uint32_t bits_of(float f)
-{
-    std::uint32_t b = 0;
-    std::memcpy(&b, &f, sizeof(b));
-    return b;
-}
-
-std::uint64_t native_bits64(const std::string& s)
-{
-    return bits_of(parse_native<double>(s));
-}
-
-std::uint32_t native_bits32(const std::string& s)
-{
-    return bits_of(parse_native<float>(s));
-}
-} // namespace
-
-TEST_CASE("parse_float_native rounds correctly")
-{
-    SECTION("double")
-    {
-        CHECK(native_bits64("1.5") == 0x3FF8000000000000u);
-        CHECK(native_bits64("0.1") == 0x3FB999999999999Au);
-        CHECK(native_bits64("-0.0") == 0x8000000000000000u);
-        CHECK(native_bits64("0e999999999999999999999") == 0u);
-        // 2^53 + 1 is exactly between two doubles: ties to even, unless more digits follow
-        CHECK(native_bits64("9007199254740993") == 0x4340000000000000u);
-        CHECK(native_bits64("9007199254740993.0000000000000000001") == 0x4340000000000001u);
-        CHECK(native_bits64("9007199254740992.9999999999999999999") == 0x4340000000000000u);
-        // 1 + 2^-53 exactly (a tie), and one unit in the 55th digit around it
-        CHECK(native_bits64("1.00000000000000011102230246251565404236316680908203125") == 0x3FF0000000000000u);
-        CHECK(native_bits64("1.00000000000000011102230246251565404236316680908203126") == 0x3FF0000000000001u);
-        CHECK(native_bits64("1.00000000000000011102230246251565404236316680908203124") == 0x3FF0000000000000u);
-        // subnormal and overflow boundaries
-        CHECK(native_bits64("2.4703282292062327e-324") == 0u);
-        CHECK(native_bits64("2.4703282292062328e-324") == 1u);
-        CHECK(native_bits64("2.2250738585072011e-308") == 0x000FFFFFFFFFFFFFu);
-        CHECK(native_bits64("2.2250738585072012e-308") == 0x0010000000000000u);
-        CHECK(native_bits64("1.7976931348623157e308") == 0x7FEFFFFFFFFFFFFFu);
-        CHECK(native_bits64("1.7976931348623159e308") == 0x7FF0000000000000u);
-        CHECK(native_bits64("-1e400") == 0xFFF0000000000000u);
-        CHECK(native_bits64("-1e-400") == 0x8000000000000000u);
-        // exponents and zeros far beyond the range cancel out
-        CHECK(native_bits64("0." + std::string(1000, '0') + "1e1001") == 0x3FF0000000000000u);
-        CHECK(native_bits64("1" + std::string(1000, '0') + "e-1000") == 0x3FF0000000000000u);
-        CHECK(native_bits64("1e-99999999999999999999999") == 0u);
-        CHECK(native_bits64("1E+99999999999999999999999") == 0x7FF0000000000000u);
-        // more digits than any midpoint has (769): only whether a nonzero digit follows matters
-        const std::string tie = "1.00000000000000011102230246251565404236316680908203125";
-        CHECK(native_bits64(tie + std::string(800, '0')) == 0x3FF0000000000000u);
-        CHECK(native_bits64(tie + std::string(800, '0') + "1") == 0x3FF0000000000001u);
-    }
-
-    SECTION("float")
-    {
-        CHECK(native_bits32("1.5") == 0x3FC00000u);
-        CHECK(native_bits32("0.1") == 0x3DCCCCCDu);
-        CHECK(native_bits32("-0.0") == 0x80000000u);
-        // 2^24 + 1 is exactly between two floats
-        CHECK(native_bits32("16777217") == 0x4B800000u);
-        CHECK(native_bits32("16777217.000000000000000000001") == 0x4B800001u);
-        CHECK(native_bits32("16777218.999999999999999999999") == 0x4B800001u);
-        CHECK(native_bits32("16777219") == 0x4B800002u);
-        // subnormal and overflow boundaries
-        CHECK(native_bits32("3.4028235677973366e38") == 0x7F7FFFFFu);
-        CHECK(native_bits32("3.4028235677973367e38") == 0x7F800000u);
-        CHECK(native_bits32("7.006492321624085e-46") == 0u);
-        CHECK(native_bits32("7.006492321624086e-46") == 1u);
-        CHECK(native_bits32("1.1754942e-38") == 0x007FFFFFu);
-        CHECK(native_bits32("-1.17549435e-38") == 0x80800000u);
-        CHECK(native_bits32("1e39") == 0x7F800000u);
-        CHECK(native_bits32("-1e-50") == 0x80000000u);
-        // not rounded through double: its double would round to another float
-        CHECK(native_bits32("1.00000005960464477539062500000000001") == 0x3F800001u);
-        CHECK(native_bits32("9007199254740993") == 0x5A000000u);
-    }
-
-    SECTION("the conversion shared with other parsers")
-    {
-        // convert_float() gives the lexer's results, for every type
-        const std::vector<std::string> tokens =
-        {
-            "0", "-0.0", "1.5", "0.1", "1e-400", "-2.5E+3", "123456789012345678901234567890",
-            "9007199254740993.0000000000000000001", "4.9406564584124654e-324"
-        };
-        using float_json = nlohmann::basic_json<std::map, std::vector, std::string, bool, std::int64_t, std::uint64_t, float>;
-        using long_double_json = nlohmann::basic_json<std::map, std::vector, std::string, bool, std::int64_t, std::uint64_t, long double>;
-        for (const auto& t : tokens)
-        {
-            CAPTURE(t);
-            const auto layout = float_token_layout(t);
-            const char* const first = t.data();
-            const char* const last = first + t.size();
-            const auto d = nlohmann::detail::convert_float<double>(first, last, layout.first, layout.second);
-            const auto f = nlohmann::detail::convert_float<float>(first, last, layout.first, layout.second);
-            const auto ld = nlohmann::detail::convert_float<long double>(first, last, layout.first, layout.second);
-            CHECK(bits_of(d) == bits_of(json::parse(t).get<double>()));
-            CHECK(bits_of(f) == bits_of(float_json::parse(t).get<float>()));
-            CHECK(ld == long_double_json::parse(t).get<long double>());
-        }
-    }
+    // numbers that are not represented exactly on the fast path
+    CHECK_FALSE(fast("12345678901234567890", out));
+    CHECK_FALSE(fast("1e10000", out));
+    CHECK_FALSE(fast("9007199254740993", out));
+    CHECK_FALSE(fast("1e23", out));
+    CHECK_FALSE(fast("1e-23", out));
 }
 
 namespace
@@ -906,6 +806,40 @@ std::size_t big_bit_length(const big_uint& a)
     }
     return n;
 }
+
+std::uint64_t bits_of(double d)
+{
+    std::uint64_t b = 0;
+    std::memcpy(&b, &d, sizeof(b));
+    return b;
+}
+
+bool eisel_lemire(const std::string& s, double& out)
+{
+    return nlohmann::detail::parse_float_eisel_lemire(s.data(), s.data() + s.size(), out);
+}
+
+// significant digits of a token, without trailing zeros
+std::size_t significant_digits(const std::string& s)
+{
+    std::string digits;
+    for (const char c : s)
+    {
+        if (c == 'e' || c == 'E')
+        {
+            break;
+        }
+        if (c >= '0' && c <= '9' && !(digits.empty() && c == '0'))
+        {
+            digits += c;
+        }
+    }
+    while (!digits.empty() && digits.back() == '0')
+    {
+        digits.pop_back();
+    }
+    return digits.size();
+}
 } // namespace
 
 TEST_CASE("Eisel-Lemire float conversion")
@@ -1303,33 +1237,26 @@ TEST_CASE("Eisel-Lemire float conversion")
         for (const auto& c : known)
         {
             CAPTURE(c.first)
-            CHECK(native_bits64(c.first) == c.second);
+            double out = 0;
+            if (eisel_lemire(c.first, out))
+            {
+                CHECK(bits_of(out) == c.second);
+            }
+            else
+            {
+                // only tokens with more than 19 significant digits are left to
+                // strtod: those whose value lies too close to a tie
+                CHECK(significant_digits(c.first) > 19);
+            }
         }
     }
 
-    SECTION("binary32")
-    {
-        using binary32 = nlohmann::detail::ieee_binary_format<24>;
-        CHECK(nlohmann::detail::eisel_lemire<binary32>(0, 1) == 0x3F800000u);
-        CHECK(nlohmann::detail::eisel_lemire<binary32>(-1, 1) == 0x3DCCCCCDu);
-        CHECK(nlohmann::detail::eisel_lemire<binary32>(-1, 15) == 0x3FC00000u);
-        CHECK(nlohmann::detail::eisel_lemire<binary32>(0, 16777217) == 0x4B800000u); // tie, to even
-        CHECK(nlohmann::detail::eisel_lemire<binary32>(0, 16777219) == 0x4B800002u); // tie, to even
-        CHECK(nlohmann::detail::eisel_lemire<binary32>(-45, 1) == 0x00000001u);
-        CHECK(nlohmann::detail::eisel_lemire<binary32>(-46, 7) == 0x00000000u);
-        CHECK(nlohmann::detail::eisel_lemire<binary32>(-46, 8) == 0x00000001u);
-        CHECK(nlohmann::detail::eisel_lemire<binary32>(-65, 9999999999999999999u) == 0x00000000u);
-        CHECK(nlohmann::detail::eisel_lemire<binary32>(20, 3402823466385288598u) == 0x7F7FFFFFu);
-        CHECK(nlohmann::detail::eisel_lemire<binary32>(20, 3402823669209384635u) == 0x7F800000u);
-        CHECK(nlohmann::detail::eisel_lemire<binary32>(39, 1) == 0x7F800000u);
-        CHECK(nlohmann::detail::eisel_lemire<binary32>(-5, 0) == 0x00000000u);
-    }
-
     SECTION("round trip")
     {
-        // every double written by to_chars and read back, and its 17-digit
-        // form with trailing digits that make the token longer than 19 digits
+        // every double written by to_chars and read back, also with trailing
+        // digits that make the token longer than 19 digits
         std::uint64_t state = 5295;
+        std::size_t declined = 0;
         for (int i = 0; i < 200000; ++i)
         {
             state ^= state << 13u;
@@ -1351,51 +1278,30 @@ TEST_CASE("Eisel-Lemire float conversion")
             const char* end = nlohmann::detail::to_chars(buffer.data(), buffer.data() + buffer.size(), d);
             const std::string token(buffer.data(), static_cast<std::size_t>(end - buffer.data()));
             CAPTURE(token)
-            CHECK(native_bits64(token) == b);
+            double out = 0;
+            REQUIRE(eisel_lemire(token, out));
+            CHECK(bits_of(out) == b);
 
-            // insert digits before the exponent of the 17-digit form: that
-            // form lies strictly inside the rounding interval of the double
-            // (the shortest one may lie on its boundary), and the digits move
-            // it by far less than the distance to the boundary, so the value
-            // must not change
-            std::array<char, 64> digits17{};
-            static_cast<void>(std::snprintf(digits17.data(), digits17.size(), "%.17g", d)); // NOLINT(cppcoreguidelines-pro-type-vararg,hicpp-vararg)
-            std::string longer = digits17.data();
+            // insert digits before the exponent: the value moves by far less
+            // than the distance to the rounding boundary, so it must not change
+            std::string longer = token;
             const std::size_t e = longer.find('e');
             const std::size_t dot = longer.find('.');
             const std::string extra = dot == std::string::npos ? ".000000000000000000001" : "000000000000000000001";
             longer.insert(e == std::string::npos ? longer.size() : e, extra);
             CAPTURE(longer)
-            CHECK(native_bits64(longer) == b);
-        }
-    }
-
-    SECTION("round trip, binary32")
-    {
-        std::uint32_t state = 5295;
-        for (int i = 0; i < 100000; ++i)
-        {
-            state ^= state << 13u;
-            state ^= state >> 17u;
-            state ^= state << 5u;
-            std::uint32_t b = state;
-            if ((b & 0x7F800000u) == 0x7F800000u)
+            if (eisel_lemire(longer, out))
             {
-                continue; // infinity or NaN
+                CHECK(bits_of(out) == b);
             }
-            if (i % 4 == 0)
+            else
             {
-                b &= 0x807FFFFFu; // subnormals
+                // w and w + 1 round differently: only when the value is very
+                // close to a rounding boundary
+                ++declined;
             }
-            float f = 0;
-            std::memcpy(&f, &b, sizeof(f));
-
-            std::array<char, 64> buffer{};
-            const char* end = nlohmann::detail::to_chars(buffer.data(), buffer.data() + buffer.size(), f);
-            const std::string token(buffer.data(), static_cast<std::size_t>(end - buffer.data()));
-            CAPTURE(token);
-            CHECK(native_bits32(token) == b);
         }
+        CHECK(declined < 1000); // 107 of the 200,000
     }
 
     SECTION("used by the lexer")
@@ -1409,76 +1315,3 @@ TEST_CASE("Eisel-Lemire float conversion")
                              "[json.exception.out_of_range.406] number overflow parsing '1.7976931348623159e308'", json::out_of_range&);
     }
 }
-
-namespace
-{
-using float_json = nlohmann::basic_json<std::map, std::vector, std::string, bool, std::int64_t, std::uint64_t, float>;
-
-// the bits of the float that parse() gives for a token, via both scanners;
-// the value must be the same for both
-template<typename Json, typename Bits>
-void check_parse(const std::string& token, Bits expected, Bits infinity)
-{
-    std::stringstream stream(token);
-    if ((expected & ~(Bits{1} << (8 * sizeof(Bits) - 1))) == infinity)
-    {
-        Json _;
-        CHECK_THROWS_WITH_AS(_ = Json::parse(token), ("[json.exception.out_of_range.406] number overflow parsing '" + token + "'").c_str(), typename Json::out_of_range&);
-        CHECK_THROWS_WITH_AS(_ = Json::parse(stream), ("[json.exception.out_of_range.406] number overflow parsing '" + token + "'").c_str(), typename Json::out_of_range&);
-        return;
-    }
-    const Json contiguous = Json::parse(token);
-    const Json streamed = Json::parse(stream);
-    if (contiguous.is_number_float()) // not an integer that fits
-    {
-        CHECK(bits_of(contiguous.template get<typename Json::number_float_t>()) == expected);
-        CHECK(bits_of(streamed.template get<typename Json::number_float_t>()) == expected);
-    }
-    else
-    {
-        CHECK(streamed.is_number_integer());
-    }
-}
-} // namespace
-
-TEST_CASE("float conversion of hard cases")
-{
-    // see float_hard_cases.hpp
-    for (const auto& c : float_hard_cases::cases())
-    {
-        const std::string token = c.token;
-        CAPTURE(token);
-        CHECK(native_bits64(token) == c.bits64);
-        CHECK(native_bits32(token) == c.bits32);
-        check_parse<json>(token, c.bits64, std::uint64_t{0x7FF0000000000000u});
-        check_parse<float_json>(token, c.bits32, std::uint32_t{0x7F800000u});
-    }
-}
-
-TEST_CASE("float overflow and underflow in the parser")
-{
-    SECTION("double")
-    {
-        check_parse<json>("1.7976931348623157e308", std::uint64_t{0x7FEFFFFFFFFFFFFFu}, std::uint64_t{0x7FF0000000000000u});
-        check_parse<json>("1.7976931348623159e308", std::uint64_t{0x7FF0000000000000u}, std::uint64_t{0x7FF0000000000000u});
-        check_parse<json>("-1e309", std::uint64_t{0xFFF0000000000000u}, std::uint64_t{0x7FF0000000000000u});
-        check_parse<json>("1" + std::string(400, '0'), std::uint64_t{0x7FF0000000000000u}, std::uint64_t{0x7FF0000000000000u});
-        check_parse<json>("1e99999999999999999999", std::uint64_t{0x7FF0000000000000u}, std::uint64_t{0x7FF0000000000000u});
-        // an underflow gives a zero with the sign of the token
-        check_parse<json>("1e-400", std::uint64_t{0}, std::uint64_t{0x7FF0000000000000u});
-        check_parse<json>("-1e-400", std::uint64_t{0x8000000000000000u}, std::uint64_t{0x7FF0000000000000u});
-        check_parse<json>("-2.4703282292062327e-324", std::uint64_t{0x8000000000000000u}, std::uint64_t{0x7FF0000000000000u});
-        check_parse<json>("0." + std::string(400, '0') + "1", std::uint64_t{0}, std::uint64_t{0x7FF0000000000000u});
-    }
-
-    SECTION("float")
-    {
-        check_parse<float_json>("3.4028234e38", std::uint32_t{0x7F7FFFFFu}, std::uint32_t{0x7F800000u});
-        check_parse<float_json>("3.4028236e38", std::uint32_t{0x7F800000u}, std::uint32_t{0x7F800000u});
-        check_parse<float_json>("-1e39", std::uint32_t{0xFF800000u}, std::uint32_t{0x7F800000u});
-        check_parse<float_json>("1e-46", std::uint32_t{0}, std::uint32_t{0x7F800000u});
-        check_parse<float_json>("-1e-46", std::uint32_t{0x80000000u}, std::uint32_t{0x7F800000u});
-        check_parse<float_json>("-7.006492321624085e-46", std::uint32_t{0x80000000u}, std::uint32_t{0x7F800000u});
-        check_parse<float_json>("-7.006492321624086e-46", std::uint32_t{0x80000001u}, std::uint32_t{0x7F800000u});
-    }
-}

tests/src/unit-locale-cpp.cpp

@@ -260,11 +260,10 @@ struct LocaleSwitchingSax final: public nlohmann::json_sax<json>
 
 TEST_CASE("locale changes between lexer construction and number conversion (#5198)")
 {
-    // float and double are converted without the locale. A long double that
-    // is not binary64 can take the strtold fallback, which honors the locale
-    // that is current at conversion time. The numbers are chosen so that it
-    // does: too many significant digits for Clinger's fast path, an underflow
-    // that std::from_chars rejects, and a plain value.
+    // The numbers are chosen so that the conversion also takes the strtod
+    // fallback, which honors the locale that is current at conversion time:
+    // too many significant digits for Clinger's fast path, an underflow that
+    // std::from_chars rejects, and a plain value.
     const std::vector<std::string> numbers = {"3.14159265358979323846", "1.5e-400", "12.34", "-0.000123456789012345678"};
     std::string text = "[";
     for (const auto& n : numbers)
@@ -328,8 +327,7 @@ TEST_CASE("locale changes between lexer construction and number conversion (#519
             }
         }
 
-        // a long double goes through std::strtold unless it is binary64 or
-        // std::from_chars supports it
+        // a long double goes through std::strtold unless std::from_chars supports it
         {
             bool switched = false;
             const auto cb = [&](int /*depth*/, long_double_json::parse_event_t event, long_double_json& /*parsed*/) noexcept
@@ -355,15 +353,8 @@ TEST_CASE("locale with a multi-byte decimal point")
 {
     // Some locales use a decimal point that is not a single character, e.g.
     // U+066B ARABIC DECIMAL SEPARATOR (two bytes in UTF-8). It cannot be
-    // substituted in place for '.', so the strtold fallback (only for long
-    // double formats other than binary64) converts a copy of the token with
-    // the whole decimal point instead (#5660). The values must be those of the
-    // "C" locale.
-    using long_double_json = nlohmann::basic_json<std::map, std::vector, std::string, bool, std::int64_t, std::uint64_t, long double>;
-    const char* const long_double_numbers = "[3.14159265358979323846, 1.5e-400, -0.000123456789012345678]";
-    REQUIRE(std::setlocale(LC_NUMERIC, "C") != nullptr);
-    const long_double_json expected_long_double = long_double_json::parse(long_double_numbers);
-
+    // substituted in place for '.', so the strtod fallback stops early. The
+    // conversion must still terminate rather than retry forever.
     const std::array<const char*, 6> names = {{"ar_EG.UTF-8", "ar_SA.UTF-8", "fa_IR.UTF-8", "ps_AF.UTF-8", "ar_EG", "fa_IR"}};
     bool tested = false;
     for (const char* name : names)
@@ -381,20 +372,12 @@ TEST_CASE("locale with a multi-byte decimal point")
         tested = true;
 
         // too many significant digits for Clinger's fast path, and an underflow
-        // that std::from_chars rejects: double does not depend on the locale
+        // that std::from_chars rejects: both reach the strtod fallback
         json j;
         CHECK_NOTHROW(j = json::parse("[3.14159265358979323846, 1.5e-400, -0.000123456789012345678]"));
         CHECK(j.is_array());
-        CHECK(j[0] == 3.14159265358979323846);
-        CHECK(j[1] == 0.0);
-        CHECK(j[2] == -0.000123456789012345678);
         CHECK(json::accept("3.14159265358979323846"));
 
-        // a long double that reaches the strtold fallback is not truncated
-        long_double_json ld;
-        CHECK_NOTHROW(ld = long_double_json::parse(long_double_numbers));
-        CHECK(ld == expected_long_double);
-
         // a value the locale-independent paths convert is not affected
         CHECK(json::parse("12.5") == 12.5);
     }

tests/src/unit-msgpack.cpp

@@ -1540,19 +1540,39 @@ TEST_CASE("MessagePack")
             CHECK_THROWS_WITH_AS(_ = json::from_msgpack(std::vector<uint8_t>({0x81})), "[json.exception.parse_error.110] parse error at byte 2: syntax error while parsing MessagePack string: unexpected end of input", json::parse_error&);
         }
 
-        SECTION("invalid UTF-8 in string (see #5529)")
+        SECTION("ill-formed UTF-8 in string (see #5529, #5651)")
         {
+            // the MessagePack specification explicitly allows a str object to
+            // contain a byte sequence that is not valid UTF-8 and expects a
+            // deserializer to hand the original bytes back unchanged; this
+            // library follows that, unlike CBOR/UBJSON/BJData/BSON, whose
+            // specifications require text strings to be valid UTF-8
+
             // a fixstr of length 2 (0xA0 | 2) whose bytes are not valid UTF-8
-            // (0xC0 0xAE is an overlong encoding of '.') must be rejected at
-            // decode time, matching every other kind of malformed binary
-            // input, rather than only failing later when the resulting
-            // value is dumped
-            json _;
-            CHECK_THROWS_WITH_AS(_ = json::from_msgpack(std::vector<uint8_t>({0xa2, 0xc0, 0xae})), "[json.exception.parse_error.113] parse error at byte 3: syntax error while parsing MessagePack string: invalid string: ill-formed UTF-8 byte", json::parse_error&);
-            CHECK(json::from_msgpack(std::vector<uint8_t>({0xa2, 0xc0, 0xae}), true, false).is_discarded());
+            // (0xC0 0xAE is an overlong encoding of '.') round-trips byte for
+            // byte as a string value
+            const std::vector<uint8_t> ill_formed_value = {0xa2, 0xc0, 0xae};
+            json j_value;
+            CHECK_NOTHROW(j_value = json::from_msgpack(ill_formed_value));
+            REQUIRE(j_value.is_string());
+            CHECK(j_value.get_ref<const json::string_t&>() == std::string("\xc0\xae"));
+            CHECK(json::from_msgpack(json::to_msgpack(j_value)) == j_value);
+            // dump() still requires valid UTF-8 and throws for such a value,
+            // unless an error handler that replaces or ignores the bytes is
+            // passed
+            CHECK_THROWS_AS(j_value.dump(), json::type_error&);
+
+            // the same bytes as an object key round-trip as well
+            const std::vector<uint8_t> ill_formed_key = {0x81, 0xa2, 0xc0, 0xae, 0x01};
+            json j_key;
+            CHECK_NOTHROW(j_key = json::from_msgpack(ill_formed_key));
+            REQUIRE(j_key.is_object());
+            CHECK(j_key.contains(std::string("\xc0\xae")));
+            CHECK(json::from_msgpack(json::to_msgpack(j_key)) == j_key);
 
             // a MessagePack bin8 blob with the very same bytes is NOT text
             // and must still be accepted as-is
+            json _;
             CHECK_NOTHROW(_ = json::from_msgpack(std::vector<uint8_t>({0xc4, 0x02, 0xc0, 0xae})));
             CHECK(_ == json::binary(std::vector<std::uint8_t>({0xc0, 0xae})));
 

tests/src/unit-ubjson.cpp

@@ -2505,6 +2505,41 @@ TEST_CASE("Universal Binary JSON Specification Examples 1")
             CHECK(json::to_ubjson(j) == v);
             CHECK(json::from_ubjson(v) == j);
         }
+
+        SECTION("ill-formed UTF-8 (see #5529, #5651)")
+        {
+            // none of the binary format specs requires a decoder to reject
+            // ill-formed UTF-8 in a text string, so a value whose bytes are
+            // not valid UTF-8 (0xC0 0xAE is an overlong encoding of '.')
+            // round-trips byte for byte as a string value; to_ubjson() is
+            // strict, so such a value cannot be written back
+            const std::vector<uint8_t> v = {'S', 'i', 2, 0xc0, 0xae};
+            json j;
+            CHECK_NOTHROW(j = json::from_ubjson(v));
+            REQUIRE(j.is_string());
+            CHECK(j.get_ref<const json::string_t&>() == std::string("\xc0\xae"));
+            CHECK_THROWS_AS(j.dump(), json::type_error&);
+            CHECK_THROWS_AS(json::to_ubjson(j), json::type_error&);
+
+            // the same bytes as an object key round-trip as well
+            const std::vector<uint8_t> v_key = {'{', 'i', 2, 0xc0, 0xae, 'i', 1, '}'};
+            json j_key;
+            CHECK_NOTHROW(j_key = json::from_ubjson(v_key));
+            REQUIRE(j_key.is_object());
+            CHECK(j_key.contains(std::string("\xc0\xae")));
+            CHECK_THROWS_AS(json::to_ubjson(j_key), json::type_error&);
+
+            CHECK_THROWS_WITH_AS(json::to_ubjson(json("\xFF")), "[json.exception.type_error.316] invalid UTF-8 byte at index 0: 0xFF", json::type_error&);
+            // a truncated multi-byte sequence
+            CHECK_THROWS_WITH_AS(json::to_ubjson(json("\xC3")), "[json.exception.type_error.316] invalid UTF-8 byte at index 0: 0xC3", json::type_error&);
+            // an encoded surrogate half (U+D800)
+            CHECK_THROWS_WITH_AS(json::to_ubjson(json("\xED\xA0\x80")), "[json.exception.type_error.316] invalid UTF-8 byte at index 0: 0xED", json::type_error&);
+            // an overlong encoding of '.'
+            CHECK_THROWS_WITH_AS(json::to_ubjson(json("\xC0\xAF")), "[json.exception.type_error.316] invalid UTF-8 byte at index 0: 0xC0", json::type_error&);
+
+            // an object key with ill-formed UTF-8 is rejected the same way
+            CHECK_THROWS_WITH_AS(json::to_ubjson(json{{"\xFF", 1}}), "[json.exception.type_error.316] invalid UTF-8 byte at index 0: 0xFF", json::type_error&);
+        }
     }
 
     SECTION("Array Type")