From: Brian Candler <b.candler@...>
Date: 2010-01-12T22:12:10+09:00
Subject: Re: How to close a TCP socket? (TCPSocket#close doesn't close it)

I単aki Baz Castillo wrote:
> But in this case when calling socket.close the connection is not 
> terminated. A
> simplified code:
> 
>   require "socket"
>   @socket = TCPSocket.new(server, port)
> 
>   Thread.new do
>     res = @socket.gets("\r\n")
>   end
> 
>   @socket.close
>   sleep 120

When I run this code, substituting a 'www.google.com' and port 80, I see 
the socket in TIME_WAIT state if I go to another terminal.

This is with
ruby 1.8.6 (2007-09-24 patchlevel 111) [i486-linux]
built from source, running under Ubuntu Hardy.

It appears to be consistent: i.e. I can ctrl-C out of the program and 
start it again, and each time I get another TIME_WAIT socket.

Whilst what you're doing is probably allowed, it's a bit ugly: one 
thread is waiting to read data from a socket at the same time as another 
closes it.

There is a more graceful way which might be useful. In the writing 
thread you can half-close the socket (@socket.close_write). If the other 
side notices this and then closes from its side, you can then finish 
reading what it sends you and  close the read side.

  require "socket"
  @socket = TCPSocket.new('smtp.example.com', 25)

  Thread.new do
    while res = @socket.gets("\r\n")
      STDERR.puts res
    end
    @socket.close_read
  end

  @socket.close_write
  sleep 120

Anyway, going back to your original code: to isolate the behaviour 
you've seen, I suggest you set up a ruby server and client pair of 
processes and connect between them (preferably using localhost). This 
makes it completely standalone and easy to reproduce by others, and 
potentially easy to fix if it is in fact a bug. Post your ruby version 
and platform too.

Regards,

Brian.
-- 
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