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https://github.com/thisismydesign/json-streamer

Ruby gem for getting data from JSON streams based on various criteria (key, nesting level, etc)
https://github.com/thisismydesign/json-streamer

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Ruby gem for getting data from JSON streams based on various criteria (key, nesting level, etc)

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# Json::Streamer



#### Ruby gem for getting data from JSON streams based on various criteria (key, nesting level, etc).



Status and support



- ✔ stable

- ✔ supported

- ✖ no ongoing development



*You are viewing the README of version [v2.1.0](https://github.com/thisismydesign/json-streamer/releases/tag/v2.1.0). You can find other releases [here](https://github.com/thisismydesign/json-streamer/releases).*



| Branch | Status |

| ------ | ------ |

| Release | [![Coverage Status](https://coveralls.io/repos/github/thisismydesign/json-streamer/badge.svg?branch=release)](https://coveralls.io/github/thisismydesign/json-streamer?branch=release)   [![Gem Version](https://badge.fury.io/rb/json-streamer.svg)](https://badge.fury.io/rb/json-streamer)   [![Total Downloads](http://ruby-gem-downloads-badge.herokuapp.com/json-streamer?type=total)](https://rubygems.org/gems/json-streamer) |

| Development | [![Build Status](https://github.com/thisismydesign/json-streamer/workflows/Test/badge.svg)](https://github.com/thisismydesign/json-streamer/actions)   [![Coverage Status](https://coveralls.io/repos/github/thisismydesign/json-streamer/badge.svg?branch=master)](https://coveralls.io/github/thisismydesign/json-streamer?branch=master) |



####  If you've tried JSON streaming with other Ruby libraries before (e.g. [JSON::Stream](https://github.com/dgraham/json-stream), [Yajl::FFI](https://github.com/dgraham/yajl-ffi))



This gem will basically spare you the need to define your own callbacks (i.e. implement an actual JSON parser using `start_object`, `end_object`, `key`, `value`, etc.).



#### If you're new to this



Streaming is useful for

- big files that do not fit in the memory (or you'd rather avoid the risk)

- files read in chunks (e.g. arriving over network)

- cases where you expect some issue with the file (e.g. losing connection to source, invalid data at some point) but would like to get as much data as possible anyway



This gem is aimed at making streaming as easy and convenient as possible.



#### Performance



Highly depends on the event generator. Out of the box the gem uses [JSON::Stream](https://github.com/dgraham/json-stream). It was chosen because it's a pure Ruby parser with no runtime dependencies. You can use any custom event generator, such as [Yajl::FFI](https://github.com/dgraham/yajl-ffi) which is dependent on the native YAJL library and is [~10 times faster](https://github.com/dgraham/yajl-ffi#performance). See the [Custom event generators](#custom-event-generators) chapter.



I did not measure the performance of my implementation on top of these libraries.



#### Dependencies



The gem's single runtime dependency is [JSON::Stream](https://github.com/dgraham/json-stream). It is only loaded if the default event generator is used.



## Installation



Add this line to your application's Gemfile:



```ruby

gem 'json-streamer'

```



And then execute:



    $ bundle



Or install it yourself as:



    $ gem install json-streamer



## Usage



```ruby

require 'json/streamer'

```



#### Passing IO upfront



Since [v1.2.0](https://github.com/thisismydesign/json-streamer/releases/tag/v1.2.0)



```ruby

file_stream = File.open('data.json', 'r')

chunk_size = 500 # defaults to 1000



streamer = Json::Streamer.parser(file_io: file_stream, chunk_size: chunk_size)

```



#### Get objects based on nesting level



```ruby

# Level zero yields the full JSON, first level yields data within the JSON 1-by-1, etc.

streamer.get(nesting_level:1) do |object|

    p object

end

```



Input:

```json

{

    "object1": "first_level_value",

    "object2": {}

}

```



Output:

```ruby

"first_level_value"

{}

```



#### Get data based on key



```ruby

streamer.get(key:'desired_key') do |object|

    p object

end

```



Input:

```json

{

    "obj1" : {

        "desired_key" : "value1"

    },

    "desired_key" : "value2",

    "obj2" : {

        "desired_key" : {

            "desired_key" : "value3"

        }

    }

}

```



Output:

```ruby

"value1"

"value2"

"value3"

{"desired_key" => "value3"}

```



#### Skip values



```ruby

streamer.get(nesting_level:1, yield_values:false) do |object|

    p object

end

```



Input:

```json

{

    "obj1" : {},

    "key" : "value"

}

```



Output:

```json

{}

```



#### Symbolize keys



Since [v1.3.0](https://github.com/thisismydesign/json-streamer/releases/tag/v1.3.0)



```ruby

streamer.get(nesting_level:0, symbolize_keys: true) do |object|

    p object

end

```



Input:

```json

{

    "obj1" : {"key" : "value"}

}

```



Output:

```ruby

{:obj1=>{:key=>"value"}}

```



#### Passing IO later (EventMachine-style)



```ruby

# Get a JsonStreamer object that provides access to the parser

# but does not start processing immediately

streamer = Json::Streamer.parser



streamer.get(nesting_level:1) do |object|

    p object

end

```



Then later in your EventMachine handler:



```ruby

def receive_data(data)

    streamer << data

end

```



#### Custom event generators



Since [v2.1.0](https://github.com/thisismydesign/json-streamer/releases/tag/v2.1.0)



```ruby

require "yajl/ffi"



Json::Streamer.parser(event_generator: Yajl::FFI::Parser.new)

```



Any parser can be used that provides the right events. The gem is tested with [Yajl::FFI](https://github.com/dgraham/yajl-ffi) and [JSON::Stream](https://github.com/dgraham/json-stream).



#### Custom yield conditions



Since [v2.0.0](https://github.com/thisismydesign/json-streamer/releases/tag/v2.0.0)



Custom conditions provide ultimate control over what to yield.



The Conditions API exposes 3 callbacks:

- `yield_value`

- `yield_array`

- `yield_object`



Each of them may be redefined. They are called once the corresponding data (value, array or object) is available. They should return whether the data should be yielded for the outside. They receive the data and the `aggregator` as parameters.



The `aggregator` exposes data about the current state of the partly parsed JSON such as:

- `level` - current level

- `key` - current key

- `value` - current value

- `key_for_level(level)` - key for custom level

- `value_for_level(level)` - value for custom level

- `get` - the raw data (in a custom format)



Example usage (inspired by [this issue](https://github.com/thisismydesign/json-streamer/issues/7#issuecomment-330232484)):



```ruby

conditions = Json::Streamer::Conditions.new

conditions.yield_value = ->(aggregator:, value:) { false }

conditions.yield_array = ->(aggregator:, array:) { false }

conditions.yield_object = lambda do |aggregator:, object:|

    aggregator.level.eql?(2) && aggregator.key_for_level(1).eql?('items1')

end



streamer.get_with_conditions(conditions) do |object|

    p object

end

```



Input:



```ruby

{

  "other": "stuff",

  "items1": [

    {

      "key1": "value"

    },

    {

      "key2": "value"

    }

  ],

  "items2": [

    {

      "key3": "value"

    },

    {

      "key4": "value"

    }

  ]

}

```



Output:



```ruby

{"key1"=>"value"}

{"key2"=>"value"}

```



#### Get an Enumerable when not passing a block



Since [v2.1.0](https://github.com/thisismydesign/json-streamer/releases/tag/v2.1.0)



When _not_ passed a block both `get` and `get_with_conditions` return an enumerator of the requested objects. When passed a block they return an empty enumerator. This means that **when _not_ passed a block the requested objects will accumulate in memory**.



Without block



```ruby

objects = streamer.get(nesting_level:1)

p objects

```



Input:

```json

{

    "object1": "first_level_value",

    "object2": {}

}

```



Output:

```ruby

["first_level_value", {}]

```



With block



```ruby

unyielded_objects = streamer.get(nesting_level:1) { |object| do_something(object) }

p unyielded_objects

```



Input:

```json

{

    "object1": "first_level_value",

    "object2": {}

}

```



Output:

```ruby

[]

```



#### Other usage information



Check the unit tests for more examples ([spec/streamer_spec.rb](spec/json/streamer/json_streamer_spec.rb)).



One `streamer` object handles one set of conditions. For multiple conditions create multiple streamers. For more details see [this discussion](https://github.com/thisismydesign/json-streamer/issues/9).



#### Deprecated API



Pre [v1.2.0](https://github.com/thisismydesign/json-streamer/releases/tag/v1.2.0)



This functionality is deprecated but kept for compatibility reasons.



```ruby

# Same as Json::Streamer.parser

streamer = Json::Streamer::JsonStreamer.new

```



```ruby

# Same as streamer << data

streamer.parser << data

```



## Contribution and feedback



This project is built around known use-cases. If you have one that isn't covered don't hesitate to open an issue and start a discussion.



Bug reports and pull requests are welcome on GitHub at https://github.com/thisismydesign/json-streamer. This project is intended to be a safe, welcoming space for collaboration, and contributors are expected to adhere to the [Contributor Covenant](http://contributor-covenant.org) code of conduct.



## Conventions



This project follows [C-Hive guides](https://github.com/c-hive/guides) for code style, way of working and other development concerns.



## License



The gem is available as open source under the terms of the [MIT License](http://opensource.org/licenses/MIT).