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Mail Archives: cygwin/2013/04/11/21:14:33

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From: Oleg Moskalenko <oleg DOT moskalenko AT citrix DOT com>
To: "cygwin AT cygwin DOT com" <cygwin AT cygwin DOT com>
Date: Thu, 11 Apr 2013 18:14:10 -0700
Subject: RE: UDP/DTLS sockets communication pattern is broken in Cygwin
Message-ID: <031222CBCF33214AB2EB4ABA279428A30140C1ACA378@SJCPMAILBOX01.citrite.net>
References: <031222CBCF33214AB2EB4ABA279428A30140C1ACA374 AT SJCPMAILBOX01 DOT citrite DOT net> <20130411212115 DOT GA1376 AT ednor DOT casa DOT cgf DOT cx>
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I am sending the test case in the attachment.=20

In the attachment, you will find source code for two programs - udpbugserve=
r and udpbugclient. "make" will build them both. They work perfectly togeth=
er in Linux, FreeBSD and Solaris. But they fail in Cygwin.

Thanks
Oleg

>=20
> On Thu, Apr 11, 2013 at 02:19:25PM -0700, Oleg Moskalenko wrote:
> >Hi All
> >
> >I found a non-standard behavior of UDP sockets in Cygwin. Normally, peop=
le =3D
> do not experience it, but the communication pattern that I am going to de=
sc=3D
> ribe here is often used in DTLS (actually, this is virtually the only way=
 t=3D o make
> OpenSSL working with DTLS on the server side), so I suppose that wit=3D h=
 the
> growing DTLS popularity people will experience the problem often.
> >
> >So this is how to reproduce the problem in "plain" UDP (without actually=
 using
> DTLS):
> >
> >1)      Server application: open a UDP socket (socket A);
> >
> >2)      Server application: bind socket A to a local server address (say,
> 172.17.17.107:3478);
> >
> >3)      Server application: wait for a packet from a client application;
> >
> >4)      Client application: open a UDP socket (socket C);
> >
> >5)      Client application: bind socket C it to a local client address (=
say,
> 168.16.16.106:12345);
> >
> >6)      Client application: send a UDP packet P1 from socket C to server=
 socket A
> (to 172.17.17.107:3478);
> >
> >7)      Server application: socket A receives the packet P1 from socket =
C;
> >
> >8)      Server application: create another UDP socket B;
> >
> >9)      Server application: bind socket B TO THE SAME LOCAL ADDRESS as s=
ocket
> A (172.17.17.107:3478);
> >
> >10)   Server application: connect socket B to the remote address of sock=
et C
> (168.16.16.106:12345) by calling connect() on the datagram socket B.
> >
> >11)   Server application: send packet P2 from socket B to socket C (to
> 168.16.16.106:12345).
> >
> >12)   Client application: on socket C, receive packet P2 from socket B (=
from
> 172.17.17.107:3478).
> >
> >13)   Client application: from socket C, send packet P3 to the server ad=
dress
> 172.17.17.107:3478.
> >
> >14)   Server application: socket A receives the packet P3 from the clien=
t socket.
> ERROR !!!
> >
> >Step 14 is wrong: the packet P3 must be delivered to socket B, because s=
ocket
> B is "connected"
> >to the remote address 168.16.16.106:12345, but socket A  is "unconnected=
".
> >Both sockets (A and B) are "bound" to the same server ad=3D dress
> >(172.17.17.107:3478) but the connected one (socket B) must be obtaining
> packets from the remote address that it is connected to.
> >
> >This is a very essential functionality for anybody who wants to implemen=
t the
> server-side DTLS communications.
> >
> >This patterns works in any OS that I tried (all FreeBSD versions, all Li=
nux
> versions and Solaris) but Cygwin fails, unfortunately.
> >
> >I am trying to migrate (port) our server application to Cygwin, and it s=
tops us
> completely. It works everywhere else.
> >
> >Please take a look if this is something that can be fixed quickly.
>=20
> How about a simple test case?
>=20
> cgf
>=20
> --
> Problem reports:       http://cygwin.com/problems.html
> FAQ:                   http://cygwin.com/faq/
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> Unsubscribe info:      http://cygwin.com/ml/#unsubscribe-simple


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