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Date:	Thu, 11 Apr 2013 17:21:15 -0400
From:	Christopher Faylor <cgf-use-the-mailinglist-please AT cygwin DOT com>
To:	cygwin AT cygwin DOT com
Subject:	Re: UDP/DTLS sockets communication pattern is broken in Cygwin
Message-ID:	<20130411212115.GA1376@ednor.casa.cgf.cx>
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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, people = do not experience it, but the communication pattern that I am going to desc= ribe here is often used in DTLS (actually, this is virtually the only way t= o make OpenSSL working with DTLS on the server side), so I suppose that wit= 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 socket A (172.17.17.107:3478);
>
>10)   Server application: connect socket B to the remote address of socket 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 address 172.17.17.107:3478.
>
>14)   Server application: socket A receives the packet P3 from the client socket. ERROR !!!
>
>Step 14 is wrong: the packet P3 must be delivered to socket B, because socket 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= 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 implement the server-side DTLS communications.
>
>This patterns works in any OS that I tried (all FreeBSD versions, all Linux  versions and Solaris) but Cygwin fails, unfortunately.
>
>I am trying to migrate (port) our server application to Cygwin, and it stops us completely. It works everywhere else.
>
>Please take a look if this is something that can be fixed quickly.

How about a simple test case?

cgf

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