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

From: Michael Tokarev <[email-masked]>
Date: Tue, 23 Jan 2007 14:10:39 +0300

Herbert Xu 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.

Well, but why getsockname() didn't just return ENOTCONN?

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

Yes it is.  But so is not returning ENOTCONN from getsockname().  I think.

/mjt