JSON implementation for Ruby

CI

Description

This is an implementation of the JSON specification according to RFC 7159 http://www.ietf.org/rfc/rfc7159.txt . There is two variants available:

  • A pure ruby variant, that relies on the strscan extensions, which is 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 a parser generated by the Ragel state machine compiler.

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.

Install the gem and add to the application's Gemfile by executing:

$ bundle add json

If bundler is not being used to manage dependencies, install the gem by executing:

$ gem install json

There is also a pure ruby json only variant of the gem, that can be installed with:

$ gem install json_pure

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).

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.

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.

Development

Release

Update the lib/json/version.rb file.

rbenv shell 2.6.5
rake build
gem push pkg/json-2.3.0.gem

rbenv shell jruby-9.2.9.0
rake build
gem push pkg/json-2.3.0-java.gem

Author

Florian Frank [email protected]

License

Ruby License, see https://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