Handling WebSocket connections in Rack

Question

The readme for faye-websocket-ruby has the below example. What does the line of code

p [:close, event.code, event.reason]

do and what does p mean there? Also what does ws.rack_response do and why is it necessary?

# app.rb
require 'faye/websocket'

App = lambda do |env|
  if Faye::WebSocket.websocket?(env)
    ws = Faye::WebSocket.new(env)

    ws.on :message do |event|
      ws.send(event.data)
    end

    ws.on :close do |event|
      p [:close, event.code, event.reason]
      ws = nil
    end

    # Return async Rack response
    ws.rack_response

  else
    # Normal HTTP request
    [200, {'Content-Type' => 'text/plain'}, ['Hello']]
  end
end

Answer 1

p() is an instance method of the Kernel class see here. It is used for printing (like puts does) but it calls the inspect method on the argument. It is useful for debugging because you can see exactly what the value is because with puts the integer 1 will be printed as "1" which is not what it is.

Every Rack application must respond to a method called call that accepts the environment env and returns an array of the form

[http_code, headers, body]

On the example above you can see that the App object is a lambda accepting the env and returning an array of the aforementioned form. Thus it is a Rack application given that a lambda has a method call.

The rack_response method does nothing more than returning a rack compatible array as you can see HERE.

More about Rack applications HERE.