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Question

Ruby TCPSocket doesn't notice it when server is killed

Answer 1

A:

I tried without the sleep function (just to make sure it wasn't putting on hold anything) and still no luck:

#!/usr/bin/env ruby
require 'rubygems'
require 'socket'
require 'activesupport' # Fixnum.seconds

sock = TCPSocket.new('127.0.0.1', 5443)
sock.sync = true

will_restart_at = Time.now + 2.seconds
should_continue = true

while should_continue
  if will_restart_at <= Time.now
    will_restart_at = Time.now + 2.seconds
    begin
      count = sock.write("ABCD ")
      puts "Wrote #{count} bytes"
    rescue Exception => myException
      puts "Exception rescued : #{myException}"
      should_continue = false
    end
  end
end

I analyzed with Wireshark and the two solutions are exactly behaving identically.

I think (and can't be sure) that until you actually call your_socket.write (which will not fail as the socket is still opened because you weren't probing for its possible destruction), the socket won't raise any error.

I tried to simulate this with nginx and manual TCP sockets. And look at that:

irb> sock = TCPSocket.new('127.0.0.1', 80)
=> #<TCPSocket:0xb743b824>
irb> sock.write("salut")
=> 5
irb> sock.read
=> "<html>\r\n<head><title>400 Bad Request</title></head>\r\n<body>\r\n</body>\r\n</html>\r\n"

# Here, I kill nginx

irb> sock.write("salut")
=> 5
irb> sock.read
=> ""
irb> sock.write("salut")
Errno::EPIPE: Broken pipe

So what's the conclusion from here? Unless you're actually expecting some data from the server, you're screwed to detect that you've lost the connection :)

Cesario 2010-03-27 21:29:04

Answer 2

+1 A:

To detect a gracefully close, you'll have to read from the socket - read returning 0 indicates the socket has closed.

If you do need know if data got sent successfully though, there's no way other than implementing ACKs of the data at the application level.

nos 2010-03-28 00:08:45

Indeed. So that pretty much means I'm screwed ? "The binary interface employs a plain TCP socket for binary content; it is streaming in nature and has zero acknowledgment responses. "http://developer.apple.com/iphone/library/documentation/NetworkingInternet/Conceptual/RemoteNotificationsPG/CommunicatingWIthAPS/CommunicatingWIthAPS.html#//apple_ref/doc/uid/TP40008194-CH101-SW3

Ecco 2010-03-28 01:00:28

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Ruby TCPSocket doesn't notice it when server is killed

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