SYLT-JSON

LOW-LEVEL JSON PARSING/TOKENIZER LIBRARY

^{And some other funky character conversion stuff, like Base-64 and Latin-1 to/from UTF-8}

Resource optimized for small 8-bit and 32-bit microcontrollers

Authors:

• D. Taylor 2018 (gmail: senseitg)

License:

• Ask and thou shalt receive

Features:

• Parses and validates JSON very fast
• Fully compliant and well tested against https://github.com/nst/JSONTestSuite
• No dynamic memory allocation
• Delivers tokens via callback
• Handles JSON in RAM as well as streaming JSON
• Designed for UTF-8

Options (*.h):

• Configurable max nesting depth
• Configurable standards-breaking optimizations
• Configurable data sizes for number representation

Resource requirements:

• Minimal memory requirements (not even 32 bytes of RAM)
• Minimal stack use (non-recursive, few local variables)
• Minimal program space (lean, compact code)
• No heap use

Notes:

• Designed for high speed, low footprint - not a rich feature set.

Caveats:

• No UTF-8 error checking - strings delivered as is
• No UTF-16
• Requires C99 to compile (-std=c99 for GCC)

Performance:

• Pretty darn good. You do the comparisons!

WhatDoesItDo™:

It takes JSON data in RAM:

char json[] = "{\"JSON\":\"We haz it\"}";
result = json_parse(json, strlen(json), print_json, NULL);

Or it takes a stream of JSON data:

char jsbuf[32]; // String extraction buffer
json_parser_ctx ctx = json_stream(jsbuf, sizeof(jsbuf), print_json, NULL);
while(!your_stream_eof()) {
  result = json_octet(&ctx, your_stream_read());
  if(result) break;
}

And delivers the contents to a custom callback function (example):

uint8_t print_json(uint32_t depth, uint8_t type, void * value, void * user) {
  uint8_t n;
  for(n = 0; n < depth; n++) printf("  ");
  switch(type) {
    case JSON_OBJECT:     printf("{"); break;
    case JSON_OBJECT_END: printf("}"); break;
    case JSON_ARRAY:      printf("["); break;
    case JSON_ARRAY_END:  printf("]"); break;
		case JSON_KEY:        printf("\"%s\" : ", json_to_string(value));
    case JSON_STRING:     printf("\"%s\"", json_to_string(value)); break;
    case JSON_NUMBER:     printf("%0.10g", json_to_double(value)); break;
    default:              printf("%s", json_const_str(type));
  }
  printf("\n");
  return JSON_OK;
}

Thus, converting this JSON string:

[null, -1.23000456789e+2, false, "Sing ♪ a \u266B song", {"var" : [0.0, 1.500, 2, {}]}]

Into this result (printed by the callback example as shown above):

[
  null
  -123.0004567
  false
  "Sing ♪ a ♫ song"
  {
    "var" : [
      0
      1.5
      2
      {
      }
    ]
  }
]

Of course, the callback function can be anything you desire.
I mostly use it to parse configuration files by implementing a small state machine that extracts all fields of interest.