Repair complete items in binary formats when parse_error() returns true (#3989)

When the SAX parser asks to recover, the binary readers now repair an
item whose end is known and read on after it, as RFC 8949, Section 5.3
describes for CBOR:

- CBOR: tags are ignored, and simple values other than false, true, and
  null become null (RFC 8949, Section 6.1); a negative integer below the
  range of number_integer_t becomes the nearest floating-point number.
- Strings that are not valid UTF-8 get U+FFFD for each ill-formed
  sequence, as in JSON text; so does a UBJSON/BJData char above 0x7F.
- UBJSON/BJData high-precision numbers keep their longest valid
  beginning (via the lexer's recover_token()), or become infinity.
- Members whose key is not a string are skipped (CBOR, MessagePack,
  BON8), like members without a key in JSON text.
- BSON elements of types the library does not read (ObjectId, datetime,
  decimal128, ...) become null; a string without its terminator and a
  document whose size does not match are kept.

Where the end of an item is unknown, reading stops as before, except
that BSON skips to the end of the document, whose size it knows.

The value read before such an error is now completed by the reader from
its container stack, as the JSON parser does, instead of by a proxy SAX
parser, which is removed. Like the parser, binary_reader gets an
AllowRecovery template parameter, so that from_*() compile without the
new code.

Tests: a table of repairs, numbers out of range, errors that stop, and
a sweep over changed and removed bytes of eight encodings that checks
balanced events and that the first error is the one from_*() reports.
All fuzzers now run a recovering checker; the binary ones also check
that it reports an error exactly when from_*() fails.

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

include/nlohmann/json.hpp

@@ -143,7 +143,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
     friend class ::nlohmann::detail::iter_impl;
     template<typename BasicJsonType, typename CharType, typename OutputSinkType>
     friend class ::nlohmann::detail::binary_writer;
-    template<typename BasicJsonType, typename InputType, typename SAX>
+    template<typename BasicJsonType, typename InputType, typename SAX, bool AllowRecovery>
     friend class ::nlohmann::detail::binary_reader;
     template<typename BasicJsonType, typename InputAdapterType>
     friend class ::nlohmann::detail::json_sax_dom_parser;
@@ -4979,26 +4979,6 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
         return parser(i.get(), nullptr, false, ignore_comments, ignore_trailing_commas, true).accept(true);
     }
 
-  private:
-    /// read a binary format and pass it to a SAX parser; if the SAX parser
-    /// asks to recover from an error, the value read so far is completed
-    /// (see detail::json_sax_salvager and #3989)
-    template<typename InputAdapterType, typename SAX>
-    static bool sax_parse_binary(InputAdapterType ia, SAX* sax,
-                                 const input_format_t format, const bool strict)
-    {
-        (void)detail::is_sax_static_asserts<SAX, basic_json> {};
-        using salvager_t = detail::json_sax_salvager<basic_json, SAX>;
-        salvager_t salvager(sax);
-        const bool result = detail::binary_reader<basic_json, InputAdapterType, salvager_t>(std::move(ia), format).sax_parse(format, &salvager, strict);
-        if (!result)
-        {
-            salvager.close_open_containers();
-        }
-        return result;
-    }
-
-  public:
     /// @brief generate SAX events
     /// @sa https://json.nlohmann.me/api/basic_json/sax_parse/
     template <typename InputType, typename SAX>
@@ -5012,7 +4992,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
         auto ia = detail::input_adapter(std::forward<InputType>(i));
         return format == input_format_t::json
                ? parser(std::move(ia), nullptr, true, ignore_comments, ignore_trailing_commas).sax_parse(sax, strict)
-               : sax_parse_binary(std::move(ia), sax, format, strict);
+               : detail::binary_reader<basic_json, decltype(ia), SAX, true>(std::move(ia), format).sax_parse(format, sax, strict);
     }
 
     /// @brief generate SAX events (iterator pair, or iterator+sentinel pair for C++20 ranges support)
@@ -5029,7 +5009,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
         auto ia = detail::input_adapter(std::move(first), std::move(last));
         return format == input_format_t::json
                ? parser(std::move(ia), nullptr, true, ignore_comments, ignore_trailing_commas).sax_parse(sax, strict)
-               : sax_parse_binary(std::move(ia), sax, format, strict);
+               : detail::binary_reader<basic_json, decltype(ia), SAX, true>(std::move(ia), format).sax_parse(format, sax, strict);
     }
 
     /// @brief generate SAX events
@@ -5051,7 +5031,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
                // NOLINTNEXTLINE(hicpp-move-const-arg,performance-move-const-arg)
                ? parser(std::move(ia), nullptr, true, ignore_comments, ignore_trailing_commas).sax_parse(sax, strict)
                // NOLINTNEXTLINE(hicpp-move-const-arg,performance-move-const-arg)
-               : sax_parse_binary(std::move(ia), sax, format, strict);
+               : detail::binary_reader<basic_json, decltype(ia), SAX, true>(std::move(ia), format).sax_parse(format, sax, strict);
     }
 #ifndef JSON_NO_IO
     /// @brief deserialize from stream