JSON implementation for Ruby 
Description
This is a implementation of the JSON specification
according to RFC 4627 www.ietf.org/rfc/rfc4627.txt
. Starting from version 1.0.0 on there will be two variants available:
-
A pure ruby variant, that relies on the iconv and the stringscan
extensions, which are both part of the ruby standard library.
-
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 www.cs.queensu.ca/~thurston/ragel
.
Both variants of the JSON 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.
All strings, that are to be encoded as JSON
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.
The JSON parsers can parse UTF-8, UTF-16BE,
UTF-16LE, UTF-32BE, and UTF-32LE JSON 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.
Installation
It’s recommended to use the extension variant of JSON, because it’s faster than the pure ruby variant.
If you cannot build it on your system, you can settle for the latter.
Just type into the command line as root:
# rake install
The above command will build the extensions and install them on your
system.
# rake install_pure
or
# ruby install.rb
will just install the pure ruby implementation of JSON.
If you use Rubygems you can type
# gem install json
instead, to install the newest JSON version.
There is also a pure ruby json only variant of the gem, that can be
installed with:
# gem install json_pure
Compiling the extensions yourself
If you want to build the extensions yourself you need rake:
You can get it from rubyforge:
http://rubyforge.org/projects/rake
or just type
# gem install rake
for the installation via rubygems.
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: www.cs.queensu.ca/~thurston/ragel
Usage
To use JSON you can
require 'json'
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
require 'json/ext'
or
require 'json/pure'
Now you can parse a JSON document into a ruby data
structure by calling
JSON.parse(document)
If you want to generate a JSON document from a ruby
data structure call
JSON.generate(data)
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).
To create a valid JSON document you have to make
sure, that the output is embedded in either a JSON
array [] or a JSON object {}. The easiest way to do
this, is by putting your values in a Ruby Array or Hash instance.
There are also the JSON and JSON[] methods which
use parse on a String or generate a JSON document
from an array or hash:
document = JSON 'test' => 23 # => "{\"test\":23}"
document = JSON['test'] => 23 # => "{\"test\":23}"
and
data = JSON '{"test":23}' # => {"test"=>23}
data = JSON['{"test":23}'] # => {"test"=>23}
You can choose to load a set of common additions to ruby core’s objects if
you
require 'json/add/core'
After requiring this you can, e. g., serialise/deserialise Ruby ranges:
JSON JSON(1..10) # => 1..10
To find out how to add JSON support to other or
your own classes, read the section “More Examples” below.
To get the best compatibility to rails’ JSON
implementation, you can
require 'json/add/rails'
Both of the additions attempt to require ‘json’ (like above) first, if it
has not been required yet.
More Examples
To create a JSON document from a ruby data
structure, you can call JSON.generate like that:
json = JSON.generate [1, 2, {"a"=>3.141}, false, true, nil, 4..10]
# => "[1,2,{\"a\":3.141},false,true,null,\"4..10\"]"
To get back a ruby data structure from a JSON
document, you have to call JSON.parse on it:
JSON.parse json
# => [1, 2, {"a"=>3.141}, false, true, nil, "4..10"]
Note, that the range from the original data structure is a simple string
now. The reason for this is, that JSON 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.
It’s possible to add JSON support serialization to
arbitrary classes by simply implementing a more specialized version of the
to_json method, that should return a JSON object (a
hash converted to JSON with to_json) like this
(don’t forget the *a for all the arguments):
class Range
def to_json(*a)
{
'json_class' => self.class.name, # = 'Range'
'data' => [ first, last, exclude_end? ]
}.to_json(*a)
end
end
The hash key ‘json_class’ is the class, that will be asked to deserialise
the JSON 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.
If a the key ‘json_class’ is found in a JSON
object, the JSON parser checks if the given class
responds to the json_create class method. If so, it is called with the JSON object converted to a Ruby hash. So a range can
be deserialised by implementing Range.json_create like this:
class Range
def self.json_create(o)
new(*o['data'])
end
end
Now it possible to serialise/deserialise ranges as well:
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]
JSON.generate 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 JSON.pretty_generate (or JSON.pretty_generate) that
creates a more readable output:
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
]
}
]
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.
The script tools/server.rb contains a small example if you want to test,
how receiving a JSON object from a webrick server
in your browser with the javasript prototype library www.prototypejs.org works.
Speed Comparisons
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:
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
In the table above 1 is JSON::Ext::Parser, 2 is YAML.load with YAML
compatbile JSON document, 3 is is JSON::Pure::Parser, 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 JSON::Pure::Parser!
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 JSON::Pure::Parser runs:
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
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:
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
In the table above 1-3 are JSON::Ext::Generator methods. 4, 6, and 7 are JSON::Pure::Generator methods and 5 is
the Rails JSON generator. It is now a bit faster
than the generator_safe and generator_pretty methods of the pure variant
but slower than the others.
To achieve the fastest JSON document output, you
can use the fast_generate method. Beware, that this will disable the
checking for circular Ruby data structures, which may cause JSON to go into an infinite loop.
Here are the median comparisons for completeness’ sake:
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
Author
Florian Frank <flori@ping.de>
License
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.
Download
The latest version of this library can be downloaded at
Online Documentation should be located at
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