# class Rack::Events

    This middleware provides hooks to certain places in the request /

response lifecycle. This is so that middleware that don't need to filter the response data can safely leave it alone and not have to send messages down the traditional “rack stack”.

The events are:

- `on_start`(request, response)

  This event is sent at the start of the request, before the next middleware in the chain is called. This method is called with a request object, and a response object. Right now, the response object is always nil, but in the future it may actually be a real response object.

- `on_commit`(request, response)

  The response has been committed. The application has returned, but the response has not been sent to the webserver yet. This method is always called with a request object and the response object. The response object is constructed from the rack triple that the application returned. Changes may still be made to the response object at this point.

- on_send(request, response)

  The webserver has started iterating over the response body and presumably has started sending data over the wire. This method is always called with a request object and the response object. The response object is constructed from the rack triple that the application returned. Changes SHOULD NOT be made to the response object as the webserver has already started sending data. Any mutations will likely result in an exception.

- `on_finish`(request, response)

  The webserver has closed the response, and all data has been written to the response socket. The request and response object should both be read-only at this point. The body MAY NOT be available on the response object as it may have been flushed to the socket.

- `on_error`(request, response, error)

  An exception has occurred in the application or an `on_commit` event. This method will get the request, the response (if available) and the exception that was raised.

## Order

`on_start` is called on the handlers in the order that they were passed to the constructor. `on_commit`, on_send`, `on_finish`, and `on_error` are called in the reverse order. `on_finish` handlers are called inside an `ensure` block, so they are guaranteed to be called even if something raises an exception. If something raises an exception in a `on_finish` method, then nothing is guaranteed.

### Public Class Methods

new(app, handlers) click to toggle source

    # File lib/rack/events.rb, line 102
    def initialize(app, handlers)
      @app      = app
      @handlers = handlers
    end

### Public Instance Methods

call(env) click to toggle source

    # File lib/rack/events.rb, line 107
    def call(env)
      request = make_request env
      on_start request, nil

      begin
        status, headers, body = @app.call request.env
        response = make_response status, headers, body
        on_commit request, response
      rescue StandardError => e
        on_error request, response, e
        on_finish request, response
        raise
      end

      body = EventedBodyProxy.new(body, request, response, @handlers) do
        on_finish request, response
      end
      [response.status, response.headers, body]
    end

### Private Instance Methods

make_request(env) click to toggle source

    # File lib/rack/events.rb, line 145
    def make_request(env)
      Rack::Request.new env
    end

make_response(status, headers, body) click to toggle source

    # File lib/rack/events.rb, line 149
    def make_response(status, headers, body)
      BufferedResponse.new status, headers, body
    end

on_commit(request, response) click to toggle source

    # File lib/rack/events.rb, line 133
    def on_commit(request, response)
      @handlers.reverse_each { |handler| handler.on_commit request, response }
    end

on_error(request, response, e) click to toggle source

    # File lib/rack/events.rb, line 129
    def on_error(request, response, e)
      @handlers.reverse_each { |handler| handler.on_error request, response, e }
    end

on_finish(request, response) click to toggle source

    # File lib/rack/events.rb, line 141
    def on_finish(request, response)
      @handlers.reverse_each { |handler| handler.on_finish request, response }
    end

on_start(request, response) click to toggle source

    # File lib/rack/events.rb, line 137
    def on_start(request, response)
      @handlers.each { |handler| handler.on_start request, nil }
    end