A fast streaming JSON parsing library in C.





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    This is YAJL 2.  For the legacy version of YAJL see

Welcome to Yet Another JSON Library (YAJL)

Why does the world need another C library for parsing JSON?

Good question. In a review of current C JSON parsing libraries I was unable to find one that satisfies my requirements. Those are, 0. written in C

  1. portable
  2. robust -- as close to "crash proof" as possible
  3. data representation independent
  4. fast
  5. generates verbose, useful error messages including context of where the error occurs in the input text.
  6. can parse JSON data off a stream, incrementally
  7. simple to use
  8. tiny

Numbers 3, 5, 6, and 7 were particularly hard to find, and were what caused me to ultimately create YAJL. This document is a tour of some of the more important aspects of YAJL.

YAJL is Free.

Permissive licensing means you can use it in open source and commercial products alike without any fees. My request beyond the licensing is that if you find bugs drop me a email, or better yet, fork and fix.

Porting YAJL should be trivial, the implementation is ANSI C. If you port to new systems I'd love to hear of it and integrate your patches.

YAJL is data representation independent.

BYODR! Many JSON libraries impose a structure based data representation on you. This is a benefit in some cases and a drawback in others. YAJL uses callbacks to remain agnostic of the in-memory representation. So if you wish to build up an in-memory representation, you may do so using YAJL, but you must bring the code that defines and populates the in memory structure.

This also means that YAJL can be used by other (higher level) JSON libraries if so desired.

YAJL supports stream parsing

This means you do not need to hold the whole JSON representation in textual form in memory. This makes YAJL ideal for filtering projects, where you're converting YAJL from one form to another (i.e. XML). The included JSON pretty printer is an example of such a filter program.

YAJL is fast

Minimal memory copying is performed. YAJL, when possible, returns pointers into the client provided text (i.e. for strings that have no embedded escape chars, hopefully the common case). I've put a lot of effort into profiling and tuning performance, but I have ignored a couple possible performance improvements to keep the interface clean, small, and flexible. My hope is that YAJL will perform comparably to the fastest JSON parser out there.

YAJL should impose both minimal CPU and memory requirements on your application.

YAJL is tiny.

Fat free. No whip.

enjoy, Lloyd - July, 2007

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