Subject: Re: why would EPIPE cause socket port to change?

From: Stephen Hemminger <[email-masked]>
Date: Tue, 23 Jan 2007 12:26:52 -0800

On Tue, 23 Jan 2007 16:44:10 +1100
Herbert Xu <[email-masked]> wrote:

> dean gaudet <[email-masked]> wrote:
> > in the test program below the getsockname result on a TCP socket changes 
> > across a write which produces EPIPE... here's a fragment of the strace:
> > 
> > getsockname(3, {sa_family=AF_INET, sin_port=htons(37636), sin_addr=inet_addr("127.0.0.1")}, [17863593746633850896]) = 0
> > ...
> > write(3, "hi!\n", 4)                    = 4
> > write(3, "hi!\n", 4)                    = -1 EPIPE (Broken pipe)
> > --- SIGPIPE (Broken pipe) @ 0 (0) ---
> > getsockname(3, {sa_family=AF_INET, sin_port=htons(59882), sin_addr=inet_addr("127.0.0.1")}, [16927060683038654480]) = 0
> > 
> > why does the port# change?  this is on 2.6.19.1.
> 
> Prior to the last write, the socket entered the CLOSED state meaning
> that the old port is no longer allocated to it.  As a result, the
> last write operates on an unconnected socket which causes a new local
> port to be allocated as an autobind.  It then fails because the socket
> is still not connected.

Why does write cause an autobind? One would think that on a
SOCK_STREAM socket, the write should just fail with ENOTCONN

> 
> So any attempt to run getsockname after an error on the socket is
> simply buggy.
> 
> Cheers,

-- 
Stephen Hemminger <[email-masked]>