JSON

A one-pass JSON parser with no memory overhead with no memory copying or allocation. The implementation is very simple but should parse any valid json input, but trades validation for efficency. One pass of the parser only reads up to the first depth of object value and pair(key,value), but deeper levels can be reached with the parsed output.

Features

- written in C
- minimal (~250 loc)
- no allocation
- utf8 support
- minimal validation

Prerequisites

To build and use the JSON parser you only need to drop the two Source files into your project and offer the following build environment:

• GCC or clang compiler
• Standard C library

Usage

First the json parser iterator needs to be initialized using the json_begin function which takes a utf8 string + length in bytes and returns the iterator.

struct json_iter iter;
iter = json_begin(json, len);

To further parse the json file there are two functions. First the json_read function which reads in the next token and returns the next iterator. json_read is useful for reading array values.

struct json_token tok;
iter = json_read(&iter, &tok);

The second parse function json_parse is for name + value pairs and uses the json_read function internally to read in two tokens. json_parse takes an iterator and a json_pair as arguments and returns the next iterator.

json_pair pair;
iter = json_parse(&iter, pair);

To access the string in the token or token pair there are two utility functions. The first function json_dup takes a read token and a allocator callback and returns a newly allocated string which contains the parsed string.

json_char *str;
str = json_dup(&tok, malloc);

The second function json_cpy takes a read token and a buffer with a maximum size to copy into and returns the number of bytes that have been copied.

json_char buf[BUF_SIZ]
int size = json_cpy(buf, BUF_SIZ, &tok);

The last two utitlity function arejson_cmp and json_type. json_cmp compares a token with a given string pointer and returns if these two are equal.

const json_char buf[] = "token";
int eq = !json_cmp(&tok, buf);

json_type returns the type a given token, but as well as the main parsing function does not perform extensive validation of content.

const enum json_typ t = json_type(&tok);

License

(The MIT License)