# Json::Streamer

#### Ruby utility that supports JSON streaming allowing you to get data based on various criteria (key, nesting level, etc).

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*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:*

The gem uses JSON::Stream's events in the background. It was chosen because it's a pure Ruby parser.
A similar implementation can be done using the ~10 times faster Yajl::FFI gem that is dependent on the native YAJL library.
I did not measure the performance of my implementation on top of these libraries.

## 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'

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

# Get a JsonStreamer object that will parse file_stream by chunks of 500
# Default chunk size in 1000
streamer = Json::Streamer::JsonStreamer.new(file_stream, 500)
```

#### Get objects based on nesting level

```ruby
# Level zero will give you the full JSON, first level will give you data within full JSON object, etc.
streamer.get(nesting_level:1) do |object|
    p object
end
```

Input:
```json
{
    "object1": "first_level_value",
    "object2": {}
}
```

Output:
```json
"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:
```json
"value1"
"value2"
"value3"
{"desired_key" : "value3"}
```

#### Skip values if you'd only like to get objects and arrays

```ruby
streamer.get(nesting_level:1, yield_values:false) do |object|
    p object
end
```

Input:
```json
{
    "obj1" : {},
    "key" : "value"
}
```

Output:
```json
{}
```

#### EventMachine-style input (since 1.1.0)

```ruby
# Get a JsonStreamer object that provides access to the parser
# but does not start processing immediately
streamer = Json::Streamer::JsonStreamer.new

streamer.get(nesting_level:1) do |object|
    p object
end
```

Then later in your EventMachine handler:

```ruby
def receive_data(data)
    streamer.parser << data
end
```

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

## Feedback

Any feedback is much appreciated.

I can only tailor this project to fit use-cases I know about - which are usually my own ones. If you find that this might be the right direction to solve your problem too but you find that it's suboptimal or lacks features don't hesitate to contact me.

Please let me know if you make use of this project so that I can prioritize further efforts.

## Development

After checking out the repo, run `bin/setup` to install dependencies. You can also run `bin/console` for an interactive prompt that will allow you to experiment.

To install this gem onto your local machine, run `bundle exec rake install`. To release a new version, update the version number in `version.rb`, and then run `bundle exec rake release`, which will create a git tag for the version, push git commits and tags, and push the `.gem` file to [rubygems.org](https://rubygems.org).

## Contributing

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.


## License

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