From: "Iñaki Baz Castillo" <ibc@...>
Date: 2010-01-13T04:22:05+09:00
Subject: TCPSocket doesn't detect remote disconnection inmediatelly

Hi, I'm experimenting an annoying issue when a server disconnects a TCP 
connection established by a Ruby client.

Let me start with an example of what I consider the expected behavior:


a) Using Linux "telnet" command:

- First connect to google.com:

~$ telnet google.com 80                                                    

  Trying 209.85.229.106...                                                                  
  Connected to google.com.                                                                  
  Escape character is '^]'.

- Then write something ("hello\n"):

  hello

- So I receive a 400 response:

  HTTP/1.0 400 Bad Request
  [...]

- And a warning:

  "Connection closed by foreign host."

- telnet exits with status 1 due to the remote disconnection error.



b) Using Ruby 1.9.1 TCPSocket:

- First connect:

  irb> require "socket"
  true
  irb> socket = TCPSocket.new("google.com", 80)
  #<TCPSocket:0x00000001010288>

- Now netstat shows the connection as ESTABLISHED (ok).

- Write "hello\n" into the socket:

  irb> socket.puts "hello"
  nil

- I receive the same 400 response from the www server. Now netstat shows the 
connection as CLOSE_WAIT (OK?).

- Write "hello\n" again (IMHO it should fail):

  irb> socket.puts "hello"
  nil          <---- didn't raise !!!

- Doing a ngrep I see that irb has sent "hello\n" over the previous TCP 
connection but this time it doesn't receive response from the www server. This 
is, irb is using a closed connection!:

  T 2010/01/12 20:12:04.072705 192.168.1.10:35272 -> 209.85.229.105:80 [AP]
  hello
  #

- But after this new "puts" now netstat shows nothing! (no connection => OK).

- Repeat again:

  irb> socket.puts "hello"
  Errno::EPIPE: Broken pipe
        from (irb):6:in `write'
        from (irb):6:in `puts'
        from (irb):6
        from /usr/bin/irb:12:in `<main>'

- Now it raises!


Why didn't Ruby raise in the second "puts" attemp??? the server already closed 
the connection! Why does Ruby realize of it after a new retry?

Well, this issue causes one request lost (the second one) since there is no 
way to know if the server accepted or dropped the request.

Is it a bug? is there a way to check the socket connection before sending 
(loosing in fact) a request? (TCPSocket#closed? is not valid here as it just 
returns true in case *we* have closed a socket).

Thanks a lot for any help.



-- 
Iñaki Baz Castillo <ibc@aliax.net>