NOTE: This library is under active development. Please don't use it for anything important!

mewjson

a tiny JSON library

Requirements

The library requires the following to compile:

CMake version 3.14 or later
C compiler with support for C11

Features

Stores whole numbers between -9223372036854775808 and 9223372036854775807, inclusive, as 64-bit signed integers
Uses a packed parse tree representation to save memory

Caveats

Only supports DOM-style (parse tree-based) parsing
Parser uses dynamic memory
Real number handling is slow and breaks in certain locales (uses strtod() and snprintf())
Parse tree is immutable

API

mewjson aims to provide a small, convenient API for parsing and validating JSON data.

Initialize a parser

The second parameter to jsonParserInit() is a pointer to struct JsonAllocator. If nonnull, the provided allocation functions are used to get memory for the parser. Otherwise, the standard C allocation routines malloc, realloc, and free are used.

struct JsonParser parser;
struct JsonAllocator a = {/* user-defined allocation functions go here */};
jsonParserInit(&parser, &a); // Must be called prior to jsonParse()

Parse a JSON document

The callbacks in h are called as values and structural elements are encountered during the parse. The input buffer does not need to be null-terminated.

static const char kJson[] = "[1,[2,[3],4],5]";
JsonDocument *doc = jsonParse(kJson, (JsonSize)strlen(kJson), &parser);
if (!doc) {
    // parser.status indicates what went wrong, and parser.offset indicates where in the input
    // buffer the parser stopped.
    fprintf(stderr, "parser error %d at offset %ld\n",
            parser.status, parser.offset);
    abort();
}

Cleanup

jsonDestroyDocument(doc);

TODO

Document the rest of the current API (jsonWrite(), jsonCloneDocument())
Prefix the document encoding with a checksum over all of its bytes
Allow direct access to the binary encoding (it can be saved and loaded, using the checksum for validation)
Consider supporting JSON patch and/or JSON merge patch
- Would have to be an API that takes 2 documents and returns another one, since the parse trees aren't easy to modify
- Makes jsonWrite() much more useful

Credits

The awesome folks on this r/C_Programming thread (posted around 6983ae8), who were kind enough to review this project
Variable-length integer encoding/decoding functions were modified from LevelDB
Logic for decoding integers is from SQLite's JSON module
Idea to use a packed representation is from SQLite's JSONB module
State transition lookup table was inspired by rapidjson
Signed varint encoding is from the Go repo

andy-byers/mewjson