JSONST - A streaming JSON library

A minimal JSON streaming parsing library with the following features and design goals:

Fully JSON compliant (whatever that means, see #standards-compliance)
Suited for embedded usage
C11, easy to use from C++
Fuzz tested
Low memory usage
No dynamic allocation (malloc)
No dependencies, not even stdlib (users have to do their own number parsing though, e.g. strtod() from <stdlib.h>)

Fully tested (GTest, C++17), passes https://github.com/nst/JSONTestSuite.

The real reason I wrote this was that I read https://nullprogram.com/blog/2023/09/27/ and wanted to play around with arena allocation in C.

Documentation & Usage

Documentation: src/jsonst.h (and other header files)
Examples: examples

No binaries are provided. To include the library in your project, simply copy the relevant files from src/:

jsonst.h, jsonst.c: Core library, this is the only thing you really need
jsonst_cstd.h: Thin wrapper to allow usage of C FILE * streams
jsonst_util.h, jsonst_util.c: Helpers to convert library ENUMs to strings

ESP-IDF component

To use this library in your ESP-IDF project, simply add it as your idf_component.yml file:

dependencies:
  jsonst:
    version: "*"
    git: https://github.com/jo-m/jsonst

Standards compliance

To the best of my knowledge, this library conforms to the following specifications:

https://www.json.org/json-en.html
https://datatracker.ietf.org/doc/html/rfc8259
- Only UTF-8 is supported
- No support for BOM
- Max length of strings incl. object keys is fixed but runtime configurable

Development

Requirements:

Bazel (https://bazel.build/install/ubuntu#install-on-ubuntu)
apt-get install clang-format clang-tidy clangd gcc g++

Commands:

# Run all tests
bazel test //...
# Build all binaries
bazel build //...
# Run clang-format
./format.sh
# Refresh compile commands database for clangd
bazel run //:refresh_compile_commands
# Run clang-tidy
bazel build //... --config clang-tidy

Inside Docker

docker run \
  -it --rm \
  --user 0 \
  --volume (pwd):/home/ubuntu/src/ \
  --workdir=/home/ubuntu/src/ \
  --entrypoint=/bin/bash \
  gcr.io/bazel-public/bazel:latest

Fuzz

sudo apt-get install afl++
cd fuzz
make

# Test the target
./fuzztarget ../src/testdata/test.json
# Get some seeds
cp bazel-src/external/com_github_nst_json_test_suite/test_*/*.json fuzz/seeds/
# FUZZ!!
echo core | sudo tee /proc/sys/kernel/core_pattern
set -x AFL_SKIP_CPUFREQ 1
afl-fuzz -i seeds/ -o fuzz_out/ -- ./fuzztarget '@@'