Question

How do I handle timeouts in an eventmachine based http server? I’m basically placing http request info on a queue on processing it, and then the processing may call a callback function, or may not. I can set a timeout time, but I have not figured out how to add a timeout handler or timeout callback.

I’ve looked through the docs but haven’t managed to glean anything useful from them. Putting logic in the unbind method obviously didn’t work as the request is complete by the time unbind is called, and adding an EM::error_handler next to the callback creation code didn’t work either.

I’d like to catch the timeout event and return specific json on a timeout event.

Here’s my code- an HTTP request handler

class HTTPRequestHandler  < EventMachine::Connection

  def initialize(s,q,h)
    @tcpserver = s
    @queue = q
    @callback_hash = h
    self.comm_inactivity_timeout = API_REQUEST_TIMEOUT

  end

  def post_init
      @parser = RequestParser.new
  end

  def receive_data(data)
    handle_http_request if @parser.parse(data)
  end

  def parse_query_parms(query_str)
    begin
      rethash = {}
      query_arr = query_str.split(/&/)
      query_arr.each { |element|
        e_arr = element.split(/\=/)
        rethash[e_arr[0]] = e_arr[1]
      }
      return rethash
    rescue
      return nil
    end
  end

  def handle_http_request
    result = parse_query_parms(@parser.env["QUERY_STRING"]) # hash
    if result
      if result.has_key?('id') and result.has_key?('rid') and result.has_key?('json')
        puts result

        # Callback to handle this
         cb = EM.Callback{ |rid,rtime,msg|
           data = "{\"rid\":\"#{rid}\",\"rtime\":\"#{rtime}\",\"msg\":#{msg}}"
           send_data("HTTP/1.1 200 OK\r\n")
           send_data("Content-Type: application/json\r\n")
           send_data("Content-Length: #{data.bytesize}\r\n")
           send_data("\r\n")
           send_data(data)
           close_connection_after_writing
         }

         # Add callback to hash
         @callback_hash[result['rid']] = cb

         # Unencode jsonin url
         json_from_api = result['json']
         json_from_api = URI.decode(json_from_api)

         # Push request onto queue
         qreq=QueuedRequest.new(result['id'],json_from_api)
         @queue.push(qreq)

      else
        data = "{\"success\":\"false\",\"response\":\"request needs id, rid, json parameters\"}"
        send_data("HTTP/1.1 200 OK\r\n")
        send_data("Content-Type: application/json\r\n")
        send_data("Content-Length: #{data.bytesize}\r\n")
        send_data("\r\n")
        send_data("#{data}")
        close_connection_after_writing
      end
    else
      data = "{\"success\":\"false\",\"response\":\"unable to parse parameters\"}"
      send_data("HTTP/1.1 200 OK\r\n")
      send_data("Content-Type: application/json\r\n")
      send_data("Content-Length: #{data.bytesize}\r\n")
      send_data("\r\n")
      send_data("#{data}")
      close_connection_after_writing
    end
  end

end

Main loop where we initialize everything and process the queue:

EM.synchrony do
  h = {} # map of rids -> callbacks for requests

  # Intialize TCP and HTTP Servers
  q = EM::Queue.new # Queue of messages from HTTP Server
  s = TCPProxyServer.new(h)
  EM.start_server(LISTEN_HOST_CLIENT, LISTEN_PORT_API, HTTPRequestHandler, s, q, h)
  s.start
  puts "Server starting (http and tcp)"

  # process queue of messages coming in from API (recursive)
  process_queue = Proc.new do |qreq| 
    # Our functions
    @operation = lambda do
      puts qreq
      begin
        # Send data to channel
        if s.connections_plug[qreq.id]
          s.connections_plug[qreq.id].send_data(qreq.json)
        else
          return "unable to find id:#{qreq.id} in connection"
        end
      rescue Exception=>e
        puts "Unable to send process queued request! #{e}"
      end     
    end
    @callback = lambda { |result| }

    EM::defer(@operation,@callback) 
    EM.next_tick{ q.pop(&process_queue) }
  end
  q.pop(&process_queue)
end

Answer 1

Upon the advice of the EventMachine group I attached a timer to my http requests:

class HTTPRequestHandler  < EventMachine::Connection
  def initialize(s,q,h)
    @tcpserver = s
    @queue = q
    @callback_hash = h
    #self.comm_inactivity_timeout = API_REQUEST_TIMEOUT # handled using one off timer
  end

  def post_init
    @parser = RequestParser.new

    # Use timer to handle timeout
    @timer = EventMachine::Timer.new API_REQUEST_TIMEOUT, proc {
      data = {:err => "timeout"}
      data = data.to_json
      send_data("HTTP/1.1 200 OK\r\n")
      send_data("Content-Type: application/json\r\n")
      send_data("Content-Length: #{data.bytesize}\r\n")
      send_data("\r\n")
      send_data("#{data}")
      close_connection_after_writing
    }
  end

  def unbind
    @timer.cancel()
  end

  def receive_data(data)
  end

end