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Niels Lohmann
63c10a51fc
* Review and extend the documentation, and check it in CI A review of all documentation pages found factual errors, dead links, missing cross-references, and gaps in examples. This fixes them and adds checks so the same problems are caught automatically. Fixes: - wrong signatures and version histories (operator!= C++20 member, binary() subtype type, get<PointerType>(), JSON_NO_THREAD_LOCAL, ...) - stale descriptions (number parsing since #5283, UBJSON table, SAX example that no longer compiled, tsl::ordered_map advice) - dead internal and external links; repology.org badges (the domain is suspended) replaced by badges that query the registries directly - deprecation notes link the migration guide; the guide itself fixed Additions: - "See also" sections, cross-references, 25 runnable examples, 12 Mermaid diagrams, new API pages for json_pointer::operator<=> and byte_container_with_subtype::operator==/!= - landing page, guides for untrusted input and performance - "unreleased" badge after versions newer than the latest release Checks: - strict documentation build (broken links/anchors fail it); CI and the publish workflow fetch the full history the build needs - weekly external link check, Mermaid syntax check in CI - check_structure.py: example titles, heading levels, alt texts, header links, docset index coverage; its unused-example check works again - all examples produce the same output on every platform Signed-off-by: Niels Lohmann <mail@nlohmann.me> * Keep the customer links that could not be fixed A dead link on the customers page is still the evidence of where the use of the library was documented. Keep the original URLs of the entries without a working replacement (Marne, Cisco Webex Desk Camera, Philips Hue, CyberArk) and exclude exactly these URLs from the link check. Signed-off-by: Niels Lohmann <mail@nlohmann.me> * Correct the duplicate-key recipe's claim about SAX positions The SAX interface's key() receives no position either; only parse_error() does. Also note that the recipe does not report the path to the repeated key (see discussion #5085). Signed-off-by: Niels Lohmann <mail@nlohmann.me> * Say the library is available as a single header and mention json_fwd.hpp Signed-off-by: Niels Lohmann <mail@nlohmann.me> * Correct documentation errors found while hunting for bugs - patch/patch_inplace: list the JSON pointer errors parse_error.106-109 and out_of_range.402/404, and quote the actual parse_error.105 message. - unflatten: list parse_error.106/107/108 and out_of_range.404. - to_bson: list out_of_range.415 (binary subtype above 255) and note that 412 and 415 are new in 3.13.0. - to_string: state that string_t must be convertible to std::string, also in the StringType requirements table. - JSON Lines: a `while (input >> j)` loop also throws after the last value for concatenated JSON values; show a loop that works for both. - BON8: a string gets 0xFF only if nothing follows it in the message; a string at the end of an array or object is ended by 0xFE. - custom_string_type.hpp: add operator+=(char), which the "Always required" list asks for (json_pointer::to_string, flatten, unflatten, and diff did not compile), and an ADL int_to_string for diff and items. Signed-off-by: Niels Lohmann <mail@nlohmann.me> * Cache the release headers with functools.lru_cache Codacy (Pylint) flagged the mutable default argument that header() used as its cache. functools.lru_cache keeps the same memoization without it. The script's output is unchanged. Signed-off-by: Niels Lohmann <mail@nlohmann.me> --------- Signed-off-by: Niels Lohmann <mail@nlohmann.me>
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6.3 KiB
BSON
BSON, short for Binary JSON, is a binary-encoded serialization of JSON-like documents. Like JSON, BSON supports the embedding of documents and arrays within other documents and arrays. BSON also contains extensions that allow representation of data types that are not part of the JSON spec. For example, BSON has a Date type and a BinData type.
!!! abstract "References"
- [BSON Website](http://bsonspec.org) - the main source on BSON
- [BSON Specification](http://bsonspec.org/spec.html) - the specification
Serialization
The library uses the following mapping from JSON values types to BSON types:
| JSON value type | value/range | BSON type | marker |
|---|---|---|---|
| null | null |
null | 0x0A |
| boolean | true, false |
boolean | 0x08 |
| number_integer | -9223372036854775808..-2147483649 | int64 | 0x12 |
| number_integer | -2147483648..2147483647 | int32 | 0x10 |
| number_integer | 2147483648..9223372036854775807 | int64 | 0x12 |
| number_unsigned | 0..2147483647 | int32 | 0x10 |
| number_unsigned | 2147483648..9223372036854775807 | int64 | 0x12 |
| number_unsigned | 9223372036854775808..18446744073709551615 | uint64 | 0x11 |
| number_float | any value | double | 0x01 |
| string | any value | string | 0x02 |
| array | any value | document | 0x04 |
| object | any value | document | 0x03 |
| binary | any value | binary | 0x05 |
!!! warning "Incomplete mapping"
The mapping is **incomplete**, since only JSON-objects (and things contained therein) can be serialized to BSON.
Also, keys may not contain U+0000, since they are serialized a zero-terminated c-strings.
!!! warning "BSON type 0x11 interoperability"
The BSON specification defines type `0x11` as a Timestamp. This library uses marker `0x11` when serializing
`number_unsigned` values in the range `9223372036854775808..18446744073709551615`. Other BSON implementations may
therefore interpret these values as Timestamps instead of unsigned integers.
!!! info "Binary values without a subtype"
BSON requires every binary value to have a subtype. If a binary value has no subtype, this library serializes it
with the generic subtype `0x00`. After deserialization, `has_subtype()` returns `true` and `subtype()` returns `0`.
As a result, serializing and deserializing a JSON object containing such a value produces a different JSON object,
even though the binary data is unchanged.
??? example "Example: serialize a JSON value to BSON"
```cpp
--8<-- "examples/to_bson.cpp"
```
Output:
```c
--8<-- "examples/to_bson.output"
```
Deserialization
The library maps BSON record types to JSON value types as follows:
| BSON type | BSON marker byte | JSON value type |
|---|---|---|
| double | 0x01 | number_float |
| string | 0x02 | string |
| document | 0x03 | object |
| array | 0x04 | array |
| binary | 0x05 | binary |
| undefined | 0x06 | unsupported |
| ObjectId | 0x07 | unsupported |
| boolean | 0x08 | boolean |
| UTC Date-Time | 0x09 | unsupported |
| null | 0x0A | null |
| Regular Expr. | 0x0B | unsupported |
| DB Pointer | 0x0C | unsupported |
| JavaScript Code | 0x0D | unsupported |
| Symbol | 0x0E | unsupported |
| JavaScript Code w/ scope | 0x0F | unsupported |
| int32 | 0x10 | number_integer |
| uint64(Timestamp) | 0x11 | number_unsigned |
| int64 | 0x12 | number_integer |
| 128-bit decimal float | 0x13 | unsupported |
| Max Key | 0x7F | unsupported |
| Min Key | 0xFF | unsupported |
!!! warning "Incomplete mapping"
The mapping is **incomplete**. The unsupported mappings are indicated in the table above.
!!! note "Handling of BSON type 0x11"
This library deserializes BSON type `0x11` (Timestamp) as a `number_unsigned` value. The 64-bit value is preserved,
but the Timestamp type information is not.
!!! warning "Lenient BSON input handling"
The BSON reader is lenient in a few areas where the BSON specification is more restrictive:
- array element keys are not checked against the required decimal sequence (`0`, `1`, `2`, ...),
- any non-zero byte is accepted as `true` for the boolean type, and
- the payload for binary subtype `0x02` is returned as-is, including its inner length prefix.
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"
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.
??? example "Example: deserialize a JSON value from BSON"
```cpp
--8<-- "examples/from_bson.cpp"
```
Output:
```json
--8<-- "examples/from_bson.output"
```