Module: JSON

Module | JSON
In: | ext/json/ext/parser/parser.c ext/json/ext/generator/generator.c ext/json/ext/parser/parser.c ext/json/ext/generator/generator.c lib/json.rb lib/json/editor.rb lib/json/common.rb lib/json/pure/generator.rb lib/json/pure/parser.rb lib/json/ext.rb lib/json/pure.rb lib/json/version.rb

# json - JSON 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 escape all non-ASCII an 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 JSON text 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.

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.

## Author

Florian Frank <flori@ping.de>

## License

This software is distributed under the same license as Ruby itself, see www.ruby-lang.org/en/LICENSE.txt.

## Download

The latest version of this library can be downloaded at

- rubyforge.org/frs?group_id=953

Online Documentation should be located at

- json.rubyforge.org

## 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'

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 Examples section 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.

## Speed Comparisons

I have created some benchmark results (see the benchmarks subdir of the package) for the JSON-Parser to estimate the speed up in the C extension:

JSON::Pure::Parser: | 28.90 calls/second
JSON::Ext::Parser: | 505.50 calls/second

This is ca. 17.5 times the speed of the pure Ruby implementation.

I have benchmarked the JSON-Generator as well. This generates a few more values, because there are different modes, that also influence the achieved speed:

- JSON::Pure::Generator:

  generate: | 35.06 calls/second
  pretty_generate: | 34.00 calls/second
  fast_generate: | 41.06 calls/second

- JSON::Ext::Generator:

  generate: | 492.11 calls/second
  pretty_generate: | 348.85 calls/second
  fast_generate: | 541.60 calls/second

- Speedup Ext/Pure:

  generate safe: | 14.0 times
  generate pretty: | 10.3 times
  generate fast: | 13.2 times

The rails framework includes a generator as well, also it seems to be rather slow: I measured only 23.87 calls/second which is slower than any of my pure generator results. Here a comparison of the different speedups with the Rails measurement as the divisor:

- Speedup Pure/Rails:

  generate safe: | 1.5 times
  generate pretty: | 1.4 times
  generate fast: | 1.7 times

- Speedup Ext/Rails:

  generate safe: | 20.6 times
  generate pretty: | 14.6 times
  generate fast: | 22.7 times

To achieve the fastest JSON text output, you can use the fast_generate/fast_unparse methods. Beware, that this will disable the checking for circular Ruby data structures, which may cause JSON to go into an infinite loop.

## Examples

To create a JSON text from a ruby data structure, you can call JSON.generate (or JSON.unparse) 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 create a valid JSON text 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.

To get back a ruby data structure from a JSON text, 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 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 unparse, and Kernel#jj for pretty_unparse 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.

### Methods

[] dump fast_generate generate load parse parse! pretty_generate restore

### Classes and Modules

Module JSON::Editor
Module JSON::Ext
Module JSON::Pure
Class JSON::CircularDatastructure
Class JSON::GeneratorError
Class JSON::JSONError
Class JSON::MissingUnicodeSupport
Class JSON::NestingError
Class JSON::ParserError

### Constants

JSON_LOADED | = | true
NaN | = | (-1.0) ** 0.5
Infinity | = | 1.0/0
MinusInfinity | = | -Infinity
UnparserError | = | GeneratorError |  | For backwards compatibility
VERSION | = | '1.1.3' |  | JSON version
VARIANT_BINARY | = | false

### Attributes

create_id | [RW] | This is create identifier, that is used to decide, if the json_create hook of a class should be called. It defaults to ‘json_class’.
generator | [R] | Returns the JSON generator modul, that is used by JSON. This might be either JSON::Ext::Generator or JSON::Pure::Generator.
parser | [R] | Returns the JSON parser class, that is used by JSON. This might be either JSON::Ext::Parser or JSON::Pure::Parser.
state | [RW] | Returns the JSON generator state class, that is used by JSON. This might be either JSON::Ext::Generator::State or JSON::Pure::Generator::State.

### Public Class methods

[](object, opts = {})

If object is string-like parse the string and return the parsed result as a Ruby data structure. Otherwise generate a JSON text from the Ruby data structure object and return it.

The opts argument is passed through to generate/parse respectively, see generate and parse for their documentation.

### Public Instance methods

dump(obj, anIO = nil, limit = nil)

Dumps obj as a JSON string, i.e. calls generate on the object and returns the result.

If anIO (an IO like object or an object that responds to the write method) was given, the resulting JSON is written to it.

If the number of nested arrays or objects exceeds limit an ArgumentError exception is raised. This argument is similar (but not exactly the same!) to the limit argument in Marshal.dump.

This method is part of the implementation of the load/dump interface of Marshal and YAML.

fast_generate(obj)

Unparse the Ruby data structure obj into a single line JSON string and return it. This method disables the checks for circles in Ruby objects, and also generates NaN, Infinity, and, -Infinity float values.

WARNING: Be careful not to pass any Ruby data structures with circles as obj argument, because this will cause JSON to go into an infinite loop.

generate(obj, state = nil)

Unparse the Ruby data structure obj into a single line JSON string and return it. state is

- a JSON::State object,
- or a Hash like object (responding to to_hash),
- an object convertible into a hash by a to_h method,

that is used as or to configure a State object.

It defaults to a state object, that creates the shortest possible JSON text in one line, checks for circular data structures and doesn‘t allow NaN, Infinity, and -Infinity.

A state hash can have the following keys:

- indent: a string used to indent levels (default: ’’),
- space: a string that is put after, a : or , delimiter (default: ’’),
- space_before: a string that is put before a : pair delimiter (default: ’’),
- object_nl: a string that is put at the end of a JSON object (default: ’’),
- array_nl: a string that is put at the end of a JSON array (default: ’’),
- check_circular: true if checking for circular data structures should be done (the default), false otherwise.
- allow_nan: true if NaN, Infinity, and -Infinity should be generated, otherwise an exception is thrown, if these values are encountered. This options defaults to false.
- max_nesting: The maximum depth of nesting allowed in the data structures from which JSON is to be generated. Disable depth checking with :max_nesting => false, it defaults to 19.

See also the fast_generate for the fastest creation method with the least amount of sanity checks, and the pretty_generate method for some defaults for a pretty output.

load(source, proc = nil)

Load a ruby data structure from a JSON source and return it. A source can either be a string-like object, an IO like object, or an object responding to the read method. If proc was given, it will be called with any nested Ruby object as an argument recursively in depth first order.

This method is part of the implementation of the load/dump interface of Marshal and YAML.

parse(source, opts = {})

Parse the JSON string source into a Ruby data structure and return it.

opts can have the following keys:

- max_nesting: The maximum depth of nesting allowed in the parsed data structures. Disable depth checking with :max_nesting => false, it defaults to 19.
- allow_nan: If set to true, allow NaN, Infinity and -Infinity in defiance of RFC 4627 to be parsed by the Parser. This option defaults to false.
- create_additions: If set to false, the Parser doesn‘t create additions even if a matchin class and create_id was found. This option defaults to true.

parse!(source, opts = {})

Parse the JSON string source into a Ruby data structure and return it. The bang version of the parse method, defaults to the more dangerous values for the opts hash, so be sure only to parse trusted source strings.

opts can have the following keys:

- max_nesting: The maximum depth of nesting allowed in the parsed data structures. Enable depth checking with :max_nesting => anInteger. The parse! methods defaults to not doing max depth checking: This can be dangerous, if someone wants to fill up your stack.
- allow_nan: If set to true, allow NaN, Infinity, and -Infinity in defiance of RFC 4627 to be parsed by the Parser. This option defaults to true.
- create_additions: If set to false, the Parser doesn‘t create additions even if a matchin class and create_id was found. This option defaults to true.

pretty_generate(obj, opts = nil)

Unparse the Ruby data structure obj into a JSON string and return it. The returned string is a prettier form of the string returned by unparse.

The opts argument can be used to configure the generator, see the generate method for a more detailed explanation.

restore(source, proc = nil)

Alias for load

[Validate]