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README.rdoc
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<h1 id="label-JSON+implementation+for+Ruby+%3Cimg+src%3D%22https%3A%2F%2Fsecure.travis-ci.org%2Fflori%2Fjson.png%22+%2F%3E"><a href="../classes/JSON.html">JSON</a> implementation for Ruby <a href="http://travis-ci.org/flori/json"><img src="https://secure.travis-ci.org/flori/json.png" /></a></h1>
<h2 id="label-Description">Description</h2>
<p>This is a implementation of the <a href="../classes/JSON.html">JSON</a>
specification according to RFC 4627 <a
href="http://www.ietf.org/rfc/rfc4627.txt">www.ietf.org/rfc/rfc4627.txt</a>
. Starting from version 1.0.0 on there will be two variants available:</p>
<ul><li>
<p>A pure ruby variant, that relies on the iconv and the stringscan
extensions, which are both part of the ruby standard library.</p>
</li><li>
<p>The quite a bit faster C extension variant, which is in parts implemented
in C and comes with its own unicode conversion functions and a parser
generated by the ragel state machine compiler <a
href="http://www.cs.queensu.ca/~thurston/ragel">www.cs.queensu.ca/~thurston/ragel</a>
.</p>
</li></ul>
<p>Both variants of the <a href="../classes/JSON.html">JSON</a> generator
generate UTF-8 character sequences by default. If an :ascii_only option
with a true value is given, they escape all non-ASCII and control
characters with uXXXX escape sequences, and support UTF-16 surrogate pairs
in order to be able to generate the whole range of unicode code points.</p>
<p>All strings, that are to be encoded as <a
href="../classes/JSON.html">JSON</a> strings, should be UTF-8 byte
sequences on the Ruby side. To encode raw binary strings, that aren’t UTF-8
encoded, please use the to_json_raw_object method of String (which produces
an object, that contains a byte array) and decode the result on the
receiving endpoint.</p>
<p>The <a href="../classes/JSON.html">JSON</a> parsers can parse UTF-8,
UTF-16BE, UTF-16LE, UTF-32BE, and UTF-32LE <a
href="../classes/JSON.html">JSON</a> documents under Ruby 1.8. Under Ruby
1.9 they take advantage of Ruby’s M17n features and can parse all documents
which have the correct String#encoding set. If a document string has
ASCII-8BIT as an encoding the parser attempts to figure out which of the
UTF encodings from above it is and trys to parse it.</p>
<h2 id="label-Installation">Installation</h2>
<p>It’s recommended to use the extension variant of <a
href="../classes/JSON.html">JSON</a>, because it’s faster than the pure
ruby variant. If you cannot build it on your system, you can settle for the
latter.</p>
<p>Just type into the command line as root:</p>
<pre># rake install</pre>
<p>The above command will build the extensions and install them on your
system.</p>
<pre># rake install_pure</pre>
<p>or</p>
<pre># ruby install.rb</pre>
<p>will just install the pure ruby implementation of <a
href="../classes/JSON.html">JSON</a>.</p>
<p>If you use Rubygems you can type</p>
<pre># gem install json</pre>
<p>instead, to install the newest <a href="../classes/JSON.html">JSON</a>
version.</p>
<p>There is also a pure ruby json only variant of the gem, that can be
installed with:</p>
<pre># gem install json_pure</pre>
<h2 id="label-Compiling+the+extensions+yourself">Compiling the extensions yourself</h2>
<p>If you want to build the extensions yourself you need rake:</p>
<pre>You can get it from rubyforge:
http://rubyforge.org/projects/rake
or just type
# gem install rake
for the installation via rubygems.</pre>
<p>If you want to create the parser.c file from its parser.rl file or draw
nice graphviz images of the state machines, you need ragel from: <a
href="http://www.cs.queensu.ca/~thurston/ragel">www.cs.queensu.ca/~thurston/ragel</a></p>
<h2 id="label-Usage">Usage</h2>
<p>To use <a href="../classes/JSON.html">JSON</a> you can</p>
<pre class="ruby"><span class="ruby-identifier">require</span> <span class="ruby-string">'json'</span>
</pre>
<p>to load the installed variant (either the extension ‘json’ or the pure
variant ‘json_pure’). If you have installed the extension variant, you can
pick either the extension variant or the pure variant by typing</p>
<pre class="ruby"><span class="ruby-identifier">require</span> <span class="ruby-string">'json/ext'</span>
</pre>
<p>or</p>
<pre class="ruby"><span class="ruby-identifier">require</span> <span class="ruby-string">'json/pure'</span>
</pre>
<p>Now you can parse a <a href="../classes/JSON.html">JSON</a> document into a
ruby data structure by calling</p>
<pre>JSON.parse(document)</pre>
<p>If you want to generate a <a href="../classes/JSON.html">JSON</a> document
from a ruby data structure call</p>
<pre>JSON.generate(data)</pre>
<p>You can also use the pretty_generate method (which formats the output more
verbosely and nicely) or fast_generate (which doesn’t do any of the
security checks generate performs, e. g. nesting deepness checks).</p>
<p>To create a valid <a href="../classes/JSON.html">JSON</a> document you have
to make sure, that the output is embedded in either a <a
href="../classes/JSON.html">JSON</a> array [] or a <a
href="../classes/JSON.html">JSON</a> object {}. The easiest way to do this,
is by putting your values in a Ruby Array or Hash instance.</p>
<p>There are also the <a href="../classes/JSON.html">JSON</a> and JSON[]
methods which use parse on a String or generate a <a
href="../classes/JSON.html">JSON</a> document from an array or hash:</p>
<pre class="ruby"><span class="ruby-identifier">document</span> = <span class="ruby-constant">JSON</span> <span class="ruby-string">'test'</span> =<span class="ruby-operator">></span> <span class="ruby-value">23</span> <span class="ruby-comment"># => "{\"test\":23}"</span>
<span class="ruby-identifier">document</span> = <span class="ruby-constant">JSON</span>[<span class="ruby-string">'test'</span>] =<span class="ruby-operator">></span> <span class="ruby-value">23</span> <span class="ruby-comment"># => "{\"test\":23}"</span>
</pre>
<p>and</p>
<pre class="ruby"><span class="ruby-identifier">data</span> = <span class="ruby-constant">JSON</span> <span class="ruby-string">'{"test":23}'</span> <span class="ruby-comment"># => {"test"=>23}</span>
<span class="ruby-identifier">data</span> = <span class="ruby-constant">JSON</span>[<span class="ruby-string">'{"test":23}'</span>] <span class="ruby-comment"># => {"test"=>23}</span>
</pre>
<p>You can choose to load a set of common additions to ruby core’s objects if
you</p>
<pre class="ruby"><span class="ruby-identifier">require</span> <span class="ruby-string">'json/add/core'</span>
</pre>
<p>After requiring this you can, e. g., serialise/deserialise Ruby ranges:</p>
<pre class="ruby"><span class="ruby-constant">JSON</span> <span class="ruby-constant">JSON</span>(<span class="ruby-value">1</span><span class="ruby-operator">..</span><span class="ruby-value">10</span>) <span class="ruby-comment"># => 1..10</span>
</pre>
<p>To find out how to add <a href="../classes/JSON.html">JSON</a> support to
other or your own classes, read the section “More Examples” below.</p>
<p>To get the best compatibility to rails’ <a
href="../classes/JSON.html">JSON</a> implementation, you can</p>
<pre class="ruby"><span class="ruby-identifier">require</span> <span class="ruby-string">'json/add/rails'</span>
</pre>
<p>Both of the additions attempt to require ‘json’ (like above) first, if it
has not been required yet.</p>
<h2 id="label-More+Examples">More Examples</h2>
<p>To create a <a href="../classes/JSON.html">JSON</a> document from a ruby
data structure, you can call <a
href="../classes/JSON.html#method-i-generate">JSON#generate</a> like that:</p>
<pre class="ruby"><span class="ruby-identifier">json</span> = <span class="ruby-constant">JSON</span>.<span class="ruby-identifier">generate</span> [<span class="ruby-value">1</span>, <span class="ruby-value">2</span>, {<span class="ruby-string">"a"</span>=<span class="ruby-operator">></span><span class="ruby-value">3.141</span>}, <span class="ruby-keyword">false</span>, <span class="ruby-keyword">true</span>, <span class="ruby-keyword">nil</span>, <span class="ruby-value">4</span><span class="ruby-operator">..</span><span class="ruby-value">10</span>]
<span class="ruby-comment"># => "[1,2,{\"a\":3.141},false,true,null,\"4..10\"]"</span>
</pre>
<p>To get back a ruby data structure from a <a
href="../classes/JSON.html">JSON</a> document, you have to call <a
href="../classes/JSON.html#method-i-parse">JSON#parse</a> on it:</p>
<pre class="ruby"><span class="ruby-constant">JSON</span>.<span class="ruby-identifier">parse</span> <span class="ruby-identifier">json</span>
<span class="ruby-comment"># => [1, 2, {"a"=>3.141}, false, true, nil, "4..10"]</span>
</pre>
<p>Note, that the range from the original data structure is a simple string
now. The reason for this is, that <a href="../classes/JSON.html">JSON</a>
doesn’t support ranges or arbitrary classes. In this case the json library
falls back to call Object#to_json, which is the same as to_s.to_json.</p>
<p>It’s possible to add <a href="../classes/JSON.html">JSON</a> support
serialization to arbitrary classes by simply implementing a more
specialized version of the to_json method, that should return a <a
href="../classes/JSON.html">JSON</a> object (a hash converted to <a
href="../classes/JSON.html">JSON</a> with to_json) like this (don’t forget
the *a for all the arguments):</p>
<pre class="ruby"><span class="ruby-keyword">class</span> <span class="ruby-constant">Range</span>
<span class="ruby-keyword">def</span> <span class="ruby-identifier">to_json</span>(*<span class="ruby-identifier">a</span>)
{
<span class="ruby-string">'json_class'</span> =<span class="ruby-operator">></span> <span class="ruby-keyword">self</span>.<span class="ruby-identifier">class</span>.<span class="ruby-identifier">name</span>, <span class="ruby-comment"># = 'Range'</span>
<span class="ruby-string">'data'</span> =<span class="ruby-operator">></span> [ <span class="ruby-identifier">first</span>, <span class="ruby-identifier">last</span>, <span class="ruby-identifier">exclude_end?</span> ]
}.<span class="ruby-identifier">to_json</span>(*<span class="ruby-identifier">a</span>)
<span class="ruby-keyword">end</span>
<span class="ruby-keyword">end</span>
</pre>
<p>The hash key ‘json_class’ is the class, that will be asked to deserialise
the <a href="../classes/JSON.html">JSON</a> representation later. In this
case it’s ‘Range’, but any namespace of the form ‘A::B’ or ‘::A::B’ will
do. All other keys are arbitrary and can be used to store the necessary
data to configure the object to be deserialised.</p>
<p>If a the key ‘json_class’ is found in a <a
href="../classes/JSON.html">JSON</a> object, the <a
href="../classes/JSON.html">JSON</a> parser checks if the given class
responds to the json_create class method. If so, it is called with the <a
href="../classes/JSON.html">JSON</a> object converted to a Ruby hash. So a
range can be deserialised by implementing <a
href="../classes/Range.html#method-c-json_create">Range.json_create</a>
like this:</p>
<pre class="ruby"><span class="ruby-keyword">class</span> <span class="ruby-constant">Range</span>
<span class="ruby-keyword">def</span> <span class="ruby-keyword">self</span>.<span class="ruby-identifier">json_create</span>(<span class="ruby-identifier">o</span>)
<span class="ruby-identifier">new</span>(*<span class="ruby-identifier">o</span>[<span class="ruby-string">'data'</span>])
<span class="ruby-keyword">end</span>
<span class="ruby-keyword">end</span>
</pre>
<p>Now it possible to serialise/deserialise ranges as well:</p>
<pre class="ruby"><span class="ruby-identifier">json</span> = <span class="ruby-constant">JSON</span>.<span class="ruby-identifier">generate</span> [<span class="ruby-value">1</span>, <span class="ruby-value">2</span>, {<span class="ruby-string">"a"</span>=<span class="ruby-operator">></span><span class="ruby-value">3.141</span>}, <span class="ruby-keyword">false</span>, <span class="ruby-keyword">true</span>, <span class="ruby-keyword">nil</span>, <span class="ruby-value">4</span><span class="ruby-operator">..</span><span class="ruby-value">10</span>]
<span class="ruby-comment"># => "[1,2,{\"a\":3.141},false,true,null,{\"json_class\":\"Range\",\"data\":[4,10,false]}]"</span>
<span class="ruby-constant">JSON</span>.<span class="ruby-identifier">parse</span> <span class="ruby-identifier">json</span>
<span class="ruby-comment"># => [1, 2, {"a"=>3.141}, false, true, nil, 4..10]</span>
</pre>
<p><a href="../classes/JSON.html#method-i-generate">JSON#generate</a> always
creates the shortest possible string representation of a ruby data
structure in one line. This is good for data storage or network protocols,
but not so good for humans to read. Fortunately there's also <a
href="../classes/JSON.html#method-i-pretty_generate">JSON#pretty_generate</a>
(or <a
href="../classes/JSON.html#method-i-pretty_generate">JSON#pretty_generate</a>)
that creates a more readable output:</p>
<pre class="ruby"><span class="ruby-identifier">puts</span> <span class="ruby-constant">JSON</span>.<span class="ruby-identifier">pretty_generate</span>([<span class="ruby-value">1</span>, <span class="ruby-value">2</span>, {<span class="ruby-string">"a"</span>=<span class="ruby-operator">></span><span class="ruby-value">3.141</span>}, <span class="ruby-keyword">false</span>, <span class="ruby-keyword">true</span>, <span class="ruby-keyword">nil</span>, <span class="ruby-value">4</span><span class="ruby-operator">..</span><span class="ruby-value">10</span>])
[
<span class="ruby-value">1</span>,
<span class="ruby-value">2</span>,
{
<span class="ruby-string">"a"</span><span class="ruby-operator">:</span> <span class="ruby-value">3.141</span>
},
<span class="ruby-keyword">false</span>,
<span class="ruby-keyword">true</span>,
<span class="ruby-identifier">null</span>,
{
<span class="ruby-string">"json_class"</span><span class="ruby-operator">:</span> <span class="ruby-string">"Range"</span>,
<span class="ruby-string">"data"</span><span class="ruby-operator">:</span> [
<span class="ruby-value">4</span>,
<span class="ruby-value">10</span>,
<span class="ruby-keyword">false</span>
]
}
]
</pre>
<p>There are also the methods Kernel#j for generate, and Kernel#jj for
pretty_generate output to the console, that work analogous to Core Ruby’s p
and the pp library’s pp methods.</p>
<p>The script tools/server.rb contains a small example if you want to test,
how receiving a <a href="../classes/JSON.html">JSON</a> object from a
webrick server in your browser with the javasript prototype library <a
href="http://www.prototypejs.org">www.prototypejs.org</a> works.</p>
<h2 id="label-Speed+Comparisons">Speed Comparisons</h2>
<p>I have created some benchmark results (see the benchmarks/data-p4-3Ghz
subdir of the package) for the JSON-parser to estimate the speed up in the
C extension:</p>
<pre>Comparing times (call_time_mean):
1 ParserBenchmarkExt#parser 900 repeats:
553.922304770 ( real) -> 21.500x
0.001805307
2 ParserBenchmarkYAML#parser 1000 repeats:
224.513358139 ( real) -> 8.714x
0.004454078
3 ParserBenchmarkPure#parser 1000 repeats:
26.755020642 ( real) -> 1.038x
0.037376163
4 ParserBenchmarkRails#parser 1000 repeats:
25.763381731 ( real) -> 1.000x
0.038814780
calls/sec ( time) -> speed covers
secs/call</pre>
<p>In the table above 1 is <a
href="../classes/JSON/Ext/Parser.html">JSON::Ext::Parser</a>, 2 is
YAML.load with YAML compatbile <a href="../classes/JSON.html">JSON</a>
document, 3 is is <a
href="../classes/JSON/Pure/Parser.html">JSON::Pure::Parser</a>, and 4 is
ActiveSupport::JSON.decode. The ActiveSupport JSON-decoder converts the
input first to YAML and then uses the YAML-parser, the conversion seems to
slow it down so much that it is only as fast as the <a
href="../classes/JSON/Pure/Parser.html">JSON::Pure::Parser</a>!</p>
<p>If you look at the benchmark data you can see that this is mostly caused by
the frequent high outliers - the median of the Rails-parser runs is still
overall smaller than the median of the <a
href="../classes/JSON/Pure/Parser.html">JSON::Pure::Parser</a> runs:</p>
<pre>Comparing times (call_time_median):
1 ParserBenchmarkExt#parser 900 repeats:
800.592479481 ( real) -> 26.936x
0.001249075
2 ParserBenchmarkYAML#parser 1000 repeats:
271.002390644 ( real) -> 9.118x
0.003690004
3 ParserBenchmarkRails#parser 1000 repeats:
30.227910865 ( real) -> 1.017x
0.033082008
4 ParserBenchmarkPure#parser 1000 repeats:
29.722384421 ( real) -> 1.000x
0.033644676
calls/sec ( time) -> speed covers
secs/call</pre>
<p>I have benchmarked the JSON-Generator as well. This generated a few more
values, because there are different modes that also influence the achieved
speed:</p>
<pre>Comparing times (call_time_mean):
1 GeneratorBenchmarkExt#generator_fast 1000 repeats:
547.354332608 ( real) -> 15.090x
0.001826970
2 GeneratorBenchmarkExt#generator_safe 1000 repeats:
443.968212317 ( real) -> 12.240x
0.002252414
3 GeneratorBenchmarkExt#generator_pretty 900 repeats:
375.104545883 ( real) -> 10.341x
0.002665923
4 GeneratorBenchmarkPure#generator_fast 1000 repeats:
49.978706968 ( real) -> 1.378x
0.020008521
5 GeneratorBenchmarkRails#generator 1000 repeats:
38.531868759 ( real) -> 1.062x
0.025952543
6 GeneratorBenchmarkPure#generator_safe 1000 repeats:
36.927649925 ( real) -> 1.018x 7 (>=3859)
0.027079979
7 GeneratorBenchmarkPure#generator_pretty 1000 repeats:
36.272134441 ( real) -> 1.000x 6 (>=3859)
0.027569373
calls/sec ( time) -> speed covers
secs/call</pre>
<p>In the table above 1-3 are <a
href="../classes/JSON/Ext/Generator.html">JSON::Ext::Generator</a> methods.
4, 6, and 7 are <a
href="../classes/JSON/Pure/Generator.html">JSON::Pure::Generator</a>
methods and 5 is the Rails <a href="../classes/JSON.html">JSON</a>
generator. It is now a bit faster than the generator_safe and
generator_pretty methods of the pure variant but slower than the others.</p>
<p>To achieve the fastest <a href="../classes/JSON.html">JSON</a> document
output, you can use the fast_generate method. Beware, that this will
disable the checking for circular Ruby data structures, which may cause <a
href="../classes/JSON.html">JSON</a> to go into an infinite loop.</p>
<p>Here are the median comparisons for completeness’ sake:</p>
<pre>Comparing times (call_time_median):
1 GeneratorBenchmarkExt#generator_fast 1000 repeats:
708.258020939 ( real) -> 16.547x
0.001411915
2 GeneratorBenchmarkExt#generator_safe 1000 repeats:
569.105020353 ( real) -> 13.296x
0.001757145
3 GeneratorBenchmarkExt#generator_pretty 900 repeats:
482.825371244 ( real) -> 11.280x
0.002071142
4 GeneratorBenchmarkPure#generator_fast 1000 repeats:
62.717626652 ( real) -> 1.465x
0.015944481
5 GeneratorBenchmarkRails#generator 1000 repeats:
43.965681162 ( real) -> 1.027x
0.022745013
6 GeneratorBenchmarkPure#generator_safe 1000 repeats:
43.929073409 ( real) -> 1.026x 7 (>=3859)
0.022763968
7 GeneratorBenchmarkPure#generator_pretty 1000 repeats:
42.802514491 ( real) -> 1.000x 6 (>=3859)
0.023363113
calls/sec ( time) -> speed covers
secs/call</pre>
<h2 id="label-Author">Author</h2>
<p>Florian Frank <<a href="mailto:flori@ping.de">flori@ping.de</a>></p>
<h2 id="label-License">License</h2>
<p>Ruby License, see the COPYING file included in the source distribution. The
Ruby License includes the GNU General Public License (GPL), Version 2, so
see the file GPL as well.</p>
<h2 id="label-Download">Download</h2>
<p>The latest version of this library can be downloaded at</p>
<ul><li>
<p><a
href="http://rubyforge.org/frs?group_id=953">rubyforge.org/frs?group_id=953</a></p>
</li></ul>
<p>Online Documentation should be located at</p>
<ul><li>
<p><a href="http://json.rubyforge.org">json.rubyforge.org</a></p>
</li></ul>
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