mirror of
https://github.com/nlohmann/json.git
synced 2026-09-25 22:05:29 +01:00
Niels Lohmann
25affee45e
to_bson() had two problems with nested values: - It recursed once per nesting level, so a value nested deeply enough - 100,000 levels on an 8 MiB stack - exhausted the call stack and terminated the process, although parse() accepts such values without complaint. - BSON prefixes every document and array with its length. The writer computed that length by walking the entire value below it, again for every nested document it wrote, which made serializing O(size x depth). A 200-level document took 30 ms instead of 1. Both passes are now iterative, and each length is computed exactly once: - calc_bson_sizes() computes the length of every document and array in one pass, each from the lengths of its entries, into a table ordered the way they are written. - write_bson_document() then writes the document, taking each length from the table. Everything observable is unchanged, as a differential test against develop confirms byte for byte: - The same bytes are written. - A key containing U+0000 still throws out_of_range.409 for the same first key, with the same diagnostics path, before anything is written. - A document too large for BSON still throws out_of_range.412 before anything is written. - A binary subtype above 255 still throws out_of_range.415 after the same partial output. Only the enclosing objects and arrays are kept on a stack, so a flat document allocates nothing for it. Measured against develop (clang -O3, median of 201 runs): flat objects unchanged, flat arrays 37% faster (the array length was computed twice), a nested 3,000-object document 2x faster, a 200-level document 33x faster. to_bson.md documented the quadratic complexity since #5334; it is linear again. Fixes #5392 for BSON, and #5308. Signed-off-by: Niels Lohmann <mail@nlohmann.me>
Documentation
Generate documentation
Note on documentation: The source files contain links to the online documentation at https://json.nlohmann.me.
This URL provides the most recent documentation and also applies to previous versions. Documentation for deprecated
functions is not removed; instead, it is marked as deprecated.
If you want to view the documentation for a specific tag or commit hash, you can generate it locally as follows (example
using tag v3.10.2):
git clone https://github.com/nlohmann/json.git
cd json
git checkout v3.10.2
make install_venv serve -C docs/mkdocs
Open http://127.0.0.1:8000/ in your browser. Replace any URL in the source code that points to
https://json.nlohmann.me with http://127.0.0.1:8000 to view the documentation for the selected tag or commit hash.