X-Recipient:	archive-cygwin AT delorie DOT com
DomainKey-Signature:	a=rsa-sha1; c=nofws; d=sourceware.org; h=list-id
	:list-unsubscribe:list-subscribe:list-archive:list-post
	:list-help:sender:date:from:to:subject:message-id:reply-to
	:references:mime-version:content-type:in-reply-to; q=dns; s=
	default; b=BXhVvyfGfFuBrkIds2AGO8xG4dA6rdvFVyJFtsdR7RRKaf/PEmldh
	IAzpRGcsjcq58hpZOFD0J+pqBJS5DikFPn/o2y9h2V2isPnRypDYjlumSNjoD1yD
	b9JHuQ+dpHIRBN6dGoNWsUO8WF61fUl79e/vOaBbpi/XI2f7J4e1xs=
DKIM-Signature:	v=1; a=rsa-sha1; c=relaxed; d=sourceware.org; h=list-id
	:list-unsubscribe:list-subscribe:list-archive:list-post
	:list-help:sender:date:from:to:subject:message-id:reply-to
	:references:mime-version:content-type:in-reply-to; s=default;
	bh=DpS9BljG8So+/ElJ9WTyVcccyZU=; b=xU0ySR19GvAsflfnWmd020vb2oDT
	iEpYRYJingr+BYX4kdbJAHXu8OGNu1yLsVZo672DT1dKFbKFo37WmgfSIIqY05+G
	DK58XbCTg5J2xecDiX0x0/Buj17Jmpjoj02q0hflh6rp3qScGFsi2Zs0ZQOwP9xo
	OndgyW1Lq7HAI+U=
Mailing-List:	contact cygwin-help AT cygwin DOT com; run by ezmlm
List-Id:	<cygwin.cygwin.com>
List-Subscribe:	<mailto:cygwin-subscribe AT cygwin DOT com>
List-Archive:	<http://sourceware.org/ml/cygwin/>
List-Post:	<mailto:cygwin AT cygwin DOT com>
List-Help:	<mailto:cygwin-help AT cygwin DOT com>, <http://sourceware.org/ml/#faqs>
Sender:	cygwin-owner AT cygwin DOT com
Mail-Followup-To:	cygwin AT cygwin DOT com
Delivered-To:	mailing list cygwin AT cygwin DOT com
Authentication-Results:	sourceware.org; auth=none
X-Virus-Found:	No
X-Spam-SWARE-Status:	No, score=-101.6 required=5.0 tests=AWL,BAYES_00,GOOD_FROM_CORINNA_CYGWIN,KAM_LAZY_DOMAIN_SECURITY,RCVD_IN_DNSWL_LOW,SPF_HELO_PASS autolearn=ham version=3.3.2 spammy=digging, observe, H*R:D*cygwin.com, H*R:U*cygwin
X-HELO:	drew.franken.de
Date:	Mon, 15 Jan 2018 21:02:49 +0100
From:	Corinna Vinschen <corinna-cygwin AT cygwin DOT com>
To:	cygwin AT cygwin DOT com
Subject:	Re: Cygwin socket option SO_REUSEADDR operates unlike Linux
Message-ID:	<20180115200249.GA3009@calimero.vinschen.de>
Reply-To:	cygwin AT cygwin DOT com
Mail-Followup-To:	cygwin AT cygwin DOT com
References:	<Pine DOT BSF DOT 4 DOT 63 DOT 1801122348420 DOT 62607 AT m0 DOT truegem DOT net> <20180113135127 DOT GA22225 AT calimero DOT vinschen DOT de> <e072e320-fca4-582d-508e-91c5c0d78bc6 AT maxrnd DOT com>
MIME-Version:	1.0
In-Reply-To:	<e072e320-fca4-582d-508e-91c5c0d78bc6@maxrnd.com>
User-Agent:	Mutt/1.9.1 (2017-09-22)

--LQksG6bCIzRHxTLp
Content-Type: text/plain; charset=utf-8
Content-Disposition: inline
Content-Transfer-Encoding: quoted-printable

On Jan 13 13:39, Mark Geisert wrote:
> Corinna Vinschen wrote:
> > On Jan 13 00:36, Mark Geisert wrote:
> > > ~ ./bindtest
> > > 1st socket is 3
> > > 1st bind OK
> > > 1st connect OK
> > > 2nd socket is 3
> > > 2nd bind OK
> > > 2nd connect: Address already in use
> > >=20
> > > ~ ./bindtest
> > > 1st socket is 3
> > > 1st bind OK
> > > 1st connect: Address already in use
> > >=20
> > > On Fedora 27, running the same STC shows:
> > >=20
> > > [mark AT lux ~]$ netstat -an|grep :111
> > > tcp        0      0 0.0.0.0:111         0.0.0.0:*        LISTEN
> > > tcp6       0      0 :::111              :::*             LISTEN
> > > udp        0      0 0.0.0.0:111         0.0.0.0:*
> > > udp6       0      0 :::111              :::*
> > > [mark AT lux ~]$ ./bindtest
> > > 1st socket is 3
> > > 1st bind OK
> > > 1st connect OK
> > > 2nd socket is 3
> > > 2nd bind OK
> > > 2nd connect OK
> >=20
> > I can't reproduce this:
> >=20
> > $ uname -sr
> > Linux 4.14.13-300.fc27.x86_64
> > $ netstat -an|grep :111
> > tcp        0      0 0.0.0.0:111             0.0.0.0:*               LIS=
TEN
> > tcp6       0      0 :::111                  :::*                    LIS=
TEN
> > udp        0      0 0.0.0.0:111             0.0.0.0:*
> > udp6       0      0 :::111                  :::*
> > $ ./bindtest
> > 1st socket is 3
> > 1st bind OK
> > 1st connect OK
> > 2nd socket is 3
> > 2nd bind OK
> > 2nd connect: Cannot assign requested address
> > [...]
> Rats.  I'll have to investigate a couple of directions, deeper.  It makes
> sense that connect() returns EADDRINUSE rather than bind() [...]

After some more digging it turns out that both of the above observations
on Linux are correct.  I can reproduce the 2nd connect succeeding by
simply adding a `sleep(1)' after the first close.  So it turns out that
Linux has a timing issue at socket cleanup which can be alleviated
by an extra sleep.  I opened a case about this issue.  EADDRNOTAVAIL
sounds a bit weird in this scenario, but it's kind of ok.

In terms of Cygwin, the EADDRINUSE is a completely different matter.

It turns out that the second connect fails because the first socket
connection is in TIME_WAIT state.  This is not exactly correct in POSIX
terms.  The TIME_WAIT connection should not disallow a new socket to
reuse the same local address.  That's what we observe on Linux (apart from
the timing issue).

But here's the problem:  Regardless if we actually use SO_REUSEADDR or
not, Windows sockets apparently disallows a subsequent connect to
succeed while the first socket is still in TIME_WAIT.  I tweaked Cygwin
to enforce SO_REUSEADDR before bind, but connect still fails with
EADDRINUSE as long as the first socket is in TIME_WAIT.

It seems the code path for listen/accept is different here compared to
connect.  Given that SO_REUSEADDR seems to cover mostly server side
scenarios, and given that I don't see this scenario discussed at all
in Steven's book, I wonder if bind/connect is a bit of a grey area.

Either way, the bottom line is that this is a WinSock restriction,
apparently.  As of today, I don't see any way around that.


Corinna

--=20
Corinna Vinschen                  Please, send mails regarding Cygwin to
Cygwin Maintainer                 cygwin AT cygwin DOT com
Red Hat

--LQksG6bCIzRHxTLp
Content-Type: application/pgp-signature; name="signature.asc"

-----BEGIN PGP SIGNATURE-----
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=Plmc
-----END PGP SIGNATURE-----

--LQksG6bCIzRHxTLp--

- Raw text -