Ruby C bindings to Yajl. An extremely efficient streaming JSON parsing library
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YAJL C Bindings for Ruby

This gem (although not in gem form just yet) is a C binding to the excellent YAJL JSON parsing and generation library.

You can read more info at the projects website or check out it's codes at

How to install

Install it like any other gem hosted at the Githubs like so:

(more instructions here:

sudo gem install brianmario-yajl-ruby

Example of use

First, you're probably gonna want to require it:

require 'yajl'


Then maybe parse some JSON from:

a File IO

json ='test.json', 'r')
parser =
hash = parser.parse(json)

or maybe a StringIO

json ="...some JSON...")
parser =
hash = parser.parse(json)

or maybe STDIN

cat someJsonFile.json | ruby -ryajl -e "puts"

Or lets say you didn't have access to the IO object that contained JSON data, but instead only had access to chunks of it at a time. No problem!

(Assume we're in an EventMachine::Connection instance)

def post_init
   @parser =

def object_parsed(obj)
   puts "Sometimes one pays most for the things one gets for nothing. - Albert Einstein"
   puts obj.inspect

def connection_completed
  # once a full JSON object has been parsed from the stream
  # object_parsed will be called, and passed the constructed object
  @parser.on_parse_complete = method(:object_parsed)

def receive_data(data)
  # continue passing chunks
  @parser << data

Or how about a JSON API HTTP request? This actually makes a request using a raw TCPSocket, then parses the JSON body right off the socket. While it's being received over the wire!

require 'uri'
require 'yajl/http_stream'

url = URI.parse("")
results = Yajl::HttpStream.get(url)

Or do the same request, with Gzip and Deflate output compression support (also supports Bzip2, if loaded): (this does the same raw socket Request, but transparently parses the compressed response body)

require 'uri'
require 'yajl/gzip'
require 'yajl/deflate'
require 'yajl/http_stream'

url = URI.parse("")
results = Yajl::HttpStream.get(url)

Since yajl-ruby parses JSON as a stream, supporting API's like Twitter's Streaming API are a piece-of-cake. You can simply supply a block to Yajl::HttpStream.get, which is used as the callback for when a JSON object has been unserialized off the stream. For the case of this Twitter Streaming API call, the callback gets fired a few times a second (depending on your connection speed). The code below is all that's needed to make the request and stream unserialized Ruby hashes off the response, continuously.

require 'uri'
require 'yajl/http_stream'

uri = URI.parse("http://#{username}:#{password}")
Yajl::HttpStream.get(uri) do |hash|
  puts hash.inspect

Or how about parsing directly from a compressed file?

require 'yajl/bzip2'

file ='some.json.bz2', 'r')
result = Yajl::Bzip2::StreamReader.parse(file)


Since yajl-ruby does everything using streams, you simply need to pass the object to encode, and the IO to write the stream to (this happens in chunks).

This allows you to encode JSON as a stream, writing directly to a socket

socket =, 9000)
hash = {:foo => 12425125, :bar => "some string", ... }
encoder =
Yajl::encoder.encode(hash, socket)

Or what if you wanted to compress the stream over the wire?

require 'yajl/gzip'
socket =, 9000)
hash = {:foo => 12425125, :bar => "some string", ... }
Yajl::Gzip::StreamWriter.encode(hash, socket)

Or what about encoding multiple objects to JSON over the same stream? This example will encode and send 50 JSON objects over the same stream, continuously.

socket =, 9000)
encoder =
50.times do
  hash = {:current_time =>, :foo => 12425125}
  encoder.encode(hash, socket)

You can also use Yajl::Bzip2::StreamWriter and Yajl::Deflate::StreamWriter. So you can pick whichever fits your CPU/bandwidth sweet-spot.

There are a lot more possibilities, some of which I'm going to write other gems/plugins for.

Some ideas are:

  • parsing logs in JSON format

  • a Rails plugin (

  • builtin Rails 3 support?

  • Rack middleware (ideally the JSON body could be handed to the parser while it's still being received)

  • use with ohai

  • JSON API clients

  • Patch Marshal#load and Marshal#dump to use JSON? ;)

  • etc…


After I finished implementation - this library performs close to the same as the current JSON.parse (C gem) does on small/medium files.

But on larger files, and higher amounts of iteration, this library was around 2x faster than JSON.parse.

The main benefit of this library is in it's memory usage. Since it's able to parse the stream in chunks, it's memory requirements are very, very low.

Here's what parsing a 2.43MB JSON file off the filesystem 20 times looks like:

Memory Usage


  • Yajl::Parser#parse: 32MB

  • JSON.parse: 54MB

  • ActiveSupport::JSON.decode: 63MB


  • Yajl::Parser#parse: 32MB

  • JSON.parse: 57MB

  • ActiveSupport::JSON.decode: 67MB

Parse Time

  • Yajl::Parser#parse: 4.54s

  • JSON.parse: 5.47s

  • ActiveSupport::JSON.decode: 64.42s

Encode Time

  • Yajl::Encoder#encode: 3.59s

  • JSON#to_json: 6.2s

  • ActiveSupport::JSON.encode: 45.58s

Compared to YAML

NOTE: I converted the 2.4MB JSON file to YAML for this test.

Parse Time (from their respective formats)

  • Yajl::Parser#parse: 4.33s

  • JSON.parse: 5.37s

  • YAML.load_stream: 19.47s

Encode Time (to their respective formats)

  • Yajl::Encoder#encode: 3.47s

  • JSON#to_json: 6.6s

  • YAML.dump(obj, io): 1309.93s

Third Party Sources Bundled

This project includes code from the BSD licensed yajl project, copyright 2007-2009 Lloyd Hilaiel

Special Thanks

I've had a lot of inspiration, and a lot of help. Thanks to everyone who's been a part of this and those to come!

  • Lloyd Hilaiel - - for writing Yajl!!

  • Josh Ferguson - - for peer-pressuring me into getting back into C; it worked ;) Also tons of support over IM

  • Jonathan Novak - - pointer-hacking help

  • Tom Smith - - pointer-hacking help

  • Rick - for making an ActiveSupport patch with support for this library and teasing me that it might go into Rails 3. You sure lit a fire under my ass and I got a ton of work done because of it! :)

  • The entire Github Crew - - my inspiration, time spent writing this, finding Yajl, So many-MANY other things wouldn't have been possible without this awesome service. I owe you guys some whiskey at Kilowatt.

  • benburkert -