JSON implementation for Ruby¶ ↑
Description¶ ↑
This is a implementation of the JSON specification according to RFC 7159 www.ietf.org/rfc/rfc7159.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 native extension variant, which is in parts implemented in C or Java and comes with its own unicode conversion functions and a parser generated by the ragel state machine compiler www.complang.org/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.
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 create the parser.c
file from its
parser.rl
file or draw nice graphviz images of the state
machines, you need ragel from: www.complang.org/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 ruby 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).
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.
Serializing exceptions¶ ↑
The JSON module doesn't extend
Exception
by default. If you convert an Exception
object to JSON, it will by default only include the
exception message.
To include the full details, you must either load the
json/add/core
mentioned above, or specifically load the
exception addition:
require 'json/add/exception'
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 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 = 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, :create_additions => true # => [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 www.ruby-lang.org/en/about/license.txt.
Download¶ ↑
The latest version of this library can be downloaded at
Online Documentation should be located at