# JSON implementation for Ruby [![CI](https://github.com/flori/json/actions/workflows/ci.yml/badge.svg)](https://github.com/flori/json/actions/workflows/ci.yml) ## Description This is a implementation of the JSON specification according to RFC 7159 http://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 http://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: http://www.complang.org/ragel/ ## Usage To use JSON you can ```ruby 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 ```ruby require 'json/ext' ``` or ```ruby require 'json/pure' ``` Now you can parse a JSON document into a ruby data structure by calling ```ruby 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: ```ruby document = JSON 'test' => 23 # => "{\"test\":23}" document = JSON['test' => 23] # => "{\"test\":23}" ``` and ```ruby 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 ```ruby require 'json/add/core' ``` After requiring this you can, e. g., serialise/deserialise Ruby ranges: ```ruby 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 ```ruby 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: ```ruby require 'json/add/exception' ``` ## More Examples To create a JSON document from a ruby data structure, you can call `JSON.generate` like that: ```ruby 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: ```ruby 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): ```ruby 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: ```ruby class Range def self.json_create(o) new(*o['data']) end end ``` Now it possible to serialise/deserialise ranges as well: ```ruby 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: ```ruby 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 JavaScript prototype library http://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 compatible 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 ``` ## Development ### Release Update the json.gemspec and json-java.gemspec. ``` 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 ## License Ruby License, see https://www.ruby-lang.org/en/about/license.txt. ## Download The latest version of this library can be downloaded at * https://rubygems.org/gems/json Online Documentation should be located at * https://www.rubydoc.info/gems/json