From: Yohanes Santoso <ysantoso-rubytalk@...>
Date: 2005-07-08T06:03:59+09:00
Subject: Re: Socket Question - close

Yohanes Santoso <ysantoso-rubytalk@dessyku.is-a-geek.org> writes:

> Detecting if the remote end has closed its side is not that
> straight-forward. 

Let me add to the above statement.

It is not straight forward for TCP connection. Other transport-level
protocol may have other mechanism to reliably detect and indicate
connection termination.

Due to difficulty in detecting connection termination in TCP,
app-level protocols running on top of TCP often has their own
mechanisms:

1. Implicit termination signal, e.g. HTTP/1.0: you send a request, the
   server returns the length of a response and then the response
   itself. Both the client and server knows that after the response is
   done, the connection is considered terminated.

2. Explicit termination signal, e.g. FTP: the client must tell the
   server that the connection is going to be terminated immediately.

3. Timed termination signal: if there is no activity for a certain
   duration, the connection is considered terminated. Usually used in
   app-level time-out mechanism.

YS.