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Add images of json_documents: save() and load()

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An image is a document stored so that loading it needs no
parsing: save() writes the node index, the text and the decoded
strings; the static load() reads an image written by save().

load() takes a pointer and size, a borrowed vector, or an owned
rvalue vector; the nodes are copied so they are aligned and can
be edited, while the text and decoded strings stay in the image.

image_check controls how much load() trusts the input: full
checks structure, bounds, strings and numbers, the parser's own
guarantees; bounds checks structure and bounds only; none skips
all checks, for images from a trusted source.

Layout is little-endian only ("NJVI" header, nodes, text, decoded
strings), following the idea of zero-copy formats such as
FlatBuffers and YaFF; the check follows FlatBuffers' Verifier.

New errors: parse_error.116 for a malformed image or a failed
check, type_error.320 for a discarded document or a big-endian
target.

A dedicated fuzzer and 6,000 seeded corruptions, checked under
ASan/UBSan, found and fixed two gaps: unchecked reserved header
fields, and unbounded null/boolean offsets that could make
dump() throw std::length_error.

Signed-off-by: Niels Lohmann <mail@nlohmann.me>
This commit is contained in:
Niels Lohmann
2026-10-06 10:48:07 +02:00
parent 6885a1576b
commit 192d178e4b
25 changed files with 2150 additions and 49 deletions
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14
docs/mkdocs/docs/api/basic_json_document/index.md
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@@ -52,10 +52,16 @@ bookkeeping edits need, and calling any of them on one fails to compile (`#!cpp
## Member functions
- [(constructor)](basic_json_document.md)
### Parsing
- [**parse**](parse.md) (_static_) - deserialize from a compatible input, borrowing or owning it as appropriate
- [**parse_copy**](parse_copy.md) (_static_) - deserialize a copy of a compatible input
- [**accept**](accept.md) (_static_) - check whether the input is valid JSON
- [**read**](read.md) - (re-)parse into this document, reusing its memory
### Access
- [**root**](root.md) - the view of the root value
- [**is_discarded**](is_discarded.md) - return whether the last parse failed
- [**source**](source.md) - the parsed text
@@ -63,6 +69,14 @@ bookkeeping edits need, and calling any of them on one fails to compile (`#!cpp
- [**node_count**](node_count.md) - the number of index entries (values plus object keys)
- [**memory_usage**](memory_usage.md) - the number of bytes held by the document
- [**shrink_to_fit**](shrink_to_fit.md) - release unused index capacity
### Images
- [**save**](save.md) - the document as an image that `load()` reads without parsing
- [**load**](load.md) (_static_) - read an image written by `save()`
### Edits
- [**set**](set.md) - replace a value, or set an object member, an array element, or the value a JSON pointer refers
to (`#!cpp Editable` documents only)
- [**push_back**](push_back.md) - append to an array (`#!cpp Editable` documents only)