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<?xml version="1.0" encoding="iso-8859-1"?>
<!DOCTYPE html
PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en">
<head>
<title>File: README</title>
<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1" />
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<body>
<div id="fileHeader">
<h1>README</h1>
<table class="header-table">
<tr class="top-aligned-row">
<td><strong>Path:</strong></td>
<td>README
</td>
</tr>
<tr class="top-aligned-row">
<td><strong>Last Update:</strong></td>
<td>Fri Feb 26 22:50:32 +0100 2010</td>
</tr>
</table>
</div>
<!-- banner header -->
<div id="bodyContent">
<div id="contextContent">
<div id="description">
<h2>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>A pure ruby variant, that relies on the iconv and the stringscan
extensions, which are both part of the ruby standard library.
</li>
<li>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>
.
</li>
</ul>
<p>
Both variants of the <a href="../classes/JSON.html">JSON</a> generator
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. This means that generated <a
href="../classes/JSON.html">JSON</a> document is encoded as UTF-8 (because
ASCII is a subset of UTF-8) and at the same time avoids decoding problems
for receiving endpoints, that don‘t expect UTF-8 encoded texts. On
the negative side this may lead to a bit longer strings than necessarry.
</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>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>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>Usage</h2>
<p>
To use <a href="../classes/JSON.html">JSON</a> you can
</p>
<pre>
require 'json'
</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>
require 'json/ext'
</pre>
<p>
or
</p>
<pre>
require 'json/pure'
</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 <a
href="../classes/JSON.html">JSON</a>[] 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>
document = JSON 'test' => 23 # => "{\"test\":23}"
document = JSON['test'] => 23 # => "{\"test\":23}"
</pre>
<p>
and
</p>
<pre>
data = JSON '{"test":23}' # => {"test"=>23}
data = JSON['{"test":23}'] # => {"test"=>23}
</pre>
<p>
You can choose to load a set of common additions to ruby core‘s
objects if you
</p>
<pre>
require 'json/add/core'
</pre>
<p>
After requiring this you can, e. g., serialise/deserialise Ruby ranges:
</p>
<pre>
JSON JSON(1..10) # => 1..10
</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>
require 'json/add/rails'
</pre>
<p>
Both of the additions attempt to require ‘json’ (like above)
first, if it has not been required yet.
</p>
<h2>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#M000098">JSON.generate</a> like that:
</p>
<pre>
json = JSON.generate [1, 2, {"a"=>3.141}, false, true, nil, 4..10]
# => "[1,2,{\"a\":3.141},false,true,null,\"4..10\"]"
</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#M000096">JSON.parse</a> on it:
</p>
<pre>
JSON.parse json
# => [1, 2, {"a"=>3.141}, false, true, nil, "4..10"]
</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 <a
href="../classes/Object.html#M000013">Object#to_json</a>, 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 Range
def to_json(*a)
{
'json_class' => self.class.name, # = 'Range'
'data' => [ first, last, exclude_end? ]
}.to_json(*a)
end
end
</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 ‘<a
href="../classes/Range.html">Range</a>’, 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#M000073">Range.json_create</a> like this:
</p>
<pre>
class Range
def self.json_create(o)
new(*o['data'])
end
end
</pre>
<p>
Now it possible to serialise/deserialise ranges as well:
</p>
<pre>
json = JSON.generate [1, 2, {"a"=>3.141}, false, true, nil, 4..10]
# => "[1,2,{\"a\":3.141},false,true,null,{\"json_class\":\"Range\",\"data\":[4,10,false]}]"
JSON.parse json
# => [1, 2, {"a"=>3.141}, false, true, nil, 4..10]
</pre>
<p>
<a href="../classes/JSON.html#M000098">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#M000100">JSON.pretty_generate</a> (or <a
href="../classes/JSON.html#M000100">JSON.pretty_generate</a>) that creates
a more readable output:
</p>
<pre>
puts JSON.pretty_generate([1, 2, {"a"=>3.141}, false, true, nil, 4..10])
[
1,
2,
{
"a": 3.141
},
false,
true,
null,
{
"json_class": "Range",
"data": [
4,
10,
false
]
}
]
</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>Speed Comparisons</h2>
<p>
I have created some benchmark results (see the benchmarks/data-p4-3Ghz
subdir of the package) for the <a
href="../classes/JSON.html">JSON</a>-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 <a
href="../classes/JSON.html">JSON</a>-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 <a href="../classes/JSON.html">JSON</a>-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>Author</h2>
<p>
Florian Frank <<a href="mailto:flori@ping.de">flori@ping.de</a>>
</p>
<h2>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>Download</h2>
<p>
The latest version of this library can be downloaded at
</p>
<ul>
<li><a
href="http://rubyforge.org/frs?group_id=953">rubyforge.org/frs?group_id=953</a>
</li>
</ul>
<p>
Online Documentation should be located at
</p>
<ul>
<li><a href="http://json.rubyforge.org">json.rubyforge.org</a>
</li>
</ul>
</div>
</div>
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