yajl

Overview

Yet Another JSON Library. YAJL is a small event-driven (SAX-style) JSON parser written in ANSI C, and a small validating JSON generator. YAJL is released under the BSD license.

Documentation

Documentation generated by doxygen from source is available for version 1.0.9.

Support

You can find Yajl on IRC in the #yajl channel on the Freenode network or you can subscribe to the Yajl mailing list by sending an email to yajl@librelist.com (more info on Librelist here)

Download

You can also clone the project with Git by running:

$ git clone git://github.com/lloyd/yajl

Features

Simple Interface

Largely because YAJL is event driven, the interface is very concise object oriented C. The interface is not cluttered with data representation, that bit is left up to higher level code. Indeed it should be possible to port most existing JSON libraries onto YAJL if so desired.

portable

It's all ANSI C. It's been successfully compiled on debian linux, OSX 10.4 i386 & ppc, OSX 10.5 i386, winXP, FreeBSD 4.10, FreeBSD 6.1 amd64, FreeBSD 7 i386, and windows vista. More platforms and binaries as time permits.

Stream parsing

YAJL remembers all state required to support restarting parsing. This allows parsing to occur incrementally as data is read off a disk or network.

Fast

A second motivation for writing YAJL, was that many available free JSON parsers fall over on large or complex inputs. YAJL is careful to minimize memory copying and input re-scanning when possible. The result is a parser that should be fast enough for most applications or tunable for any application. On my mac pro (2.66 ghz) it takes 1s to verify a 60meg json file. Minimizing that same file with json_reformat takes 4s.

Low resource consumption

Largely because YAJL deals with streams, it's possible to parse JSON in low memory environments. Oftentimes with other parsers an application must hold both the input text and the memory representation of the tree in memory at one time. With YAJL you can incrementally read the input stream and hold only the in memory representation. Or for filtering or validation tasks, it's not required to hold the entire input text in memory.

sample programs

included in the source are a couple sample programs to demonstrate and test yajl:
json_reformat: a minimizer and beautifier in one.
json_verify: a JSON verifier.

comments in JSON

If you're dead set on using JSON throughout your system, you'll probably end up using it for your configuration files too. A little crazy, perhaps. But so am I. At parser allocation time you may specify a configuration parameter to allow comments inside the JSON input text. This is supported in versions 0.2.0 and above.

Example Programmatic Usage In C

#include <yajl/yajl_parse.h>
#include <yajl/yajl_gen.h>
 
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

static int reformat_null(void * ctx)
{
    yajl_gen g = (yajl_gen) ctx;
    yajl_gen_null(g);
    return 1;
}

static int reformat_boolean(void * ctx, int boolean)
{
    yajl_gen g = (yajl_gen) ctx;
    yajl_gen_bool(g, boolean);
    return 1;
}

static int reformat_number(void * ctx, const char * s, unsigned int l)
{
    yajl_gen g = (yajl_gen) ctx;
    yajl_gen_number(g, s, l);
    return 1;
}

static int reformat_string(void * ctx, const unsigned char * stringVal,
                           unsigned int stringLen)
{
    yajl_gen g = (yajl_gen) ctx;
    yajl_gen_string(g, stringVal, stringLen);
    return 1;
}

static int reformat_map_key(void * ctx, const unsigned char * stringVal,
                            unsigned int stringLen)
{
    yajl_gen g = (yajl_gen) ctx;
    yajl_gen_string(g, stringVal, stringLen);
    return 1;
}

static int reformat_start_map(void * ctx)
{
    yajl_gen g = (yajl_gen) ctx;
    yajl_gen_map_open(g);
    return 1;
}

static int reformat_end_map(void * ctx)
{
    yajl_gen g = (yajl_gen) ctx;
    yajl_gen_map_close(g);
    return 1;
}

static int reformat_start_array(void * ctx)
{
    yajl_gen g = (yajl_gen) ctx;
    yajl_gen_array_open(g);
    return 1;
}

static int reformat_end_array(void * ctx)
{
    yajl_gen g = (yajl_gen) ctx;
    yajl_gen_array_close(g);
    return 1;
}

static yajl_callbacks callbacks = {
    reformat_null,
    reformat_boolean,
    NULL,
    NULL,
    reformat_number,
    reformat_string,
    reformat_start_map,
    reformat_map_key,
    reformat_end_map,
    reformat_start_array,
    reformat_end_array
};

static void
usage(const char * progname)
{
    fprintf(stderr, "usage:  %s <filename>\n"
            "    -m minimize json rather than beautify (default)\n"
            "    -u allow invalid UTF8 inside strings during parsing\n",
            progname);
    exit(1);

}
 
int 
main(int argc, char ** argv)
{
    yajl_handle hand;
    static unsigned char fileData[65536];
    /* generator config */
    yajl_gen_config conf = { 1, "  " };
  yajl_gen g;
    yajl_status stat;
    size_t rd;
    /* allow comments */
    yajl_parser_config cfg = { 1, 1 };
    int done = 0;
    
    /* check arguments.  We expect exactly one! */
    if (argc == 2) {
        if (!strcmp("-m", argv[1])) {
            conf.beautify = 0;

} else if (!strcmp("-u", argv[1])) {
            cfg.checkUTF8 = 0;
        } else {
            usage(argv[0]);
        }
    } else if (argc != 1) {
        usage(argv[0]);
    }
    
    g = yajl_gen_alloc(&conf, NULL);
 
    /* ok.  open file.  let's read and parse */
    hand = yajl_alloc(&callbacks, &cfg,  NULL, (void *) g);
        
	while (!done) {
        rd = fread((void *) fileData, 1, sizeof(fileData) - 1, stdin);
        
        if (rd == 0) {
            if (!feof(stdin)) {
                fprintf(stderr, "error on file read.\n");
                break;
            }
            done = 1;
        }
        fileData[rd] = 0;
        
        if (done)
            /* parse any remaining buffered data */
            stat = yajl_parse_complete(hand);
        else
            /* read file data, pass to parser */
            stat = yajl_parse(hand, fileData, rd);

if (stat != yajl_status_ok &&
            stat != yajl_status_insufficient_data)
        {
            unsigned char * str = yajl_get_error(hand, 1, fileData, rd);
            fprintf(stderr, (const char *) str);
            yajl_free_error(hand, str);
        } else {
            const unsigned char * buf;
            unsigned int len;
            yajl_gen_get_buf(g, &buf, &len);
            fwrite(buf, 1, len, stdout);
            yajl_gen_clear(g);
        }
    }

yajl_gen_free(g);
    yajl_free(hand);
    
    return 0;
}

License

 Copyright 2007-2009, Lloyd Hilaiel.
 
 Redistribution and use in source and binary forms, with or without
 modification, are permitted provided that the following conditions are
 met:
 
  1. Redistributions of source code must retain the above copyright
     notice, this list of conditions and the following disclaimer.
 
  2. Redistributions in binary form must reproduce the above copyright
     notice, this list of conditions and the following disclaimer in
     the documentation and/or other materials provided with the
     distribution.
 
  3. Neither the name of Lloyd Hilaiel nor the names of its
     contributors may be used to endorse or promote products derived
     from this software without specific prior written permission.
 
 THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
 IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
 WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
 DISCLAIMED. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT,
 INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
 (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
 SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
 STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING
 IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
 POSSIBILITY OF SUCH DAMAGE.

Related projects

yajl-ruby - ruby bindings for YAJL
yajl-objc - Objective-C bindings for YAJL
YAJL IO bindings (for the IO language)
Python bindings come in two flavors, py-yajl OR yajl-py
yajl-js - node.js bindings (mirrored to github).
lua-yajl - lua bindings
ooc-yajl - ooc bindings

Contributors

Many people have helped hone yajl to a fine edge, they have my deep appreciation for taking the time to give back. Here they are in alphabetical order (if I missed anyone, please tell me. It's been a while and my memory is bad):

Adam McLaurin
Andrei Soroker
Brian Lopez (@brianmario)
Eric Bergstrome
Hatem Nassrat
Mark de Does
Neville Franks
R. Tyler Ballance (@rtyler)
Randall E. Barker (@bluemarvin)
Rick (@technoweenie)
Robert Geiger
Robert Varga
Timothy J. Wood

Original Author

Lloyd Hilaiel (lloyd 4t hilaiel d0t com)