From: Andrew Edwards <andrew@...>
Date: 2009-05-19T19:31:05+09:00
Subject: Detect TCPSocket interruptions/disappearance

Hi,

I am putting together a background daemon as part of a Rails app to
handle monitoring of our phone system. The phone system exposes an TCP
socket on which it delivers lines of text in real-time corresponding
to events (new call etc).

I have put together a skeleton process to monitor this, shown below.
However I am not sure how to reliably detect when the phone system
goes away, say it is rebooted or similar.

In such a case the code simply hangs on the gets request within the
loop and never returns.

When the phone system is visible again the original connection is
either lost or timed-out, hence nothing is submitted for the daemon to
receive. Ideally I need to detect this and re-open a connection via
the daemon.

Is the gets method even the best method for this scenario?

I had considered having a separate thread monitoring the visibility of
the server and if it disappears signal to cycle the connection.
Although I'm sure there may be a better way...

Any thoughts much appreciated, Andrew.


begin

  TCPSocket::open("192.168.10.130", 4005) do |socket|

    $running = true

    Signal.trap("TERM") do
      $running = false
      socket.close
    end

    socket.puts "LOGIN,\n"
    if socket.gets == "LOGINOK\n"
      ActiveRecord::Base.logger.info "Successful Login, Start Monitor"
      while($running) do
        routing_message = socket.gets
        ActiveRecord::Base.logger.info DateTime.now.to_s + " " +
routing_message
      end
      ActiveRecord::Base.logger.info "Stop Monitor"
    else
      ActiveRecord::Base.logger.info "Failed Login"
    end

  end

rescue *ErrorsOnSocket => err
  ActiveRecord::Base.logger.info "Socket Error, Retrying..."
  sleep 15
  retry
end