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Date: Mon, 22 Mar 2010 10:56:37 -0400
From: Charles Wilson <cygwin AT cwilson DOT fastmail DOT fm>
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Subject: Re: recvfrom + MSG_PEEK = broken?
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On 3/22/2010 7:03 AM, Corinna Vinschen wrote:
> On Mar 22 02:04, Charles Wilson wrote:
>> I've been tracking down a problem in xinetd. It appears to be an issue
>> with using MSG_PEEK in recvfrom() on UDP sockets.
> 
> Yes, that's a bug in Cygwin.  The socket event handling got messed up
> when MSG_PEEK was used.  I fixed that in CVS so it will be in 1.7.2.

Confirmed: fixes both my testcase, and the error in xinetd. Thanks for
the quick turnaround!  I was about ready to pull my hair out on this
problem, because I just couldn't see what xinetd was doing wrong, and
debugging networking daemons is...not fun.

This also is a partial explanation for some of the oddities we were
seing with libwrap, and IPv6/IPv4/IPv4-in-IPv6 connections.  Not all of
them, so there's still some (application level) work to do, but I'm
getting there.

> The last time I had problems with MSG_PEEK was back in 2006.  Curious
> how seldomly it's used, apparently.

Well, it didn't appear to cause a problem in xinetd wrt TCP connections,
only UDP.  And who -- except me -- tries to test the builtin servers
like 'daytime' and 'echo', over UDP?  If you're smart, you don't even
enable those services...

> Thanks for the simple testcase!  It was very helpful to track down
> the problem easily.

Glad to hear it.

--
Chuck

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