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. Thanks! Oleg Moskalenko -- Problem reports: http://cygwin.com/problems.html FAQ: http://cygwin.com/faq/ Documentation: http://cygwin.com/docs.html Unsubscribe info: http://cygwin.com/ml/#unsubscribe-simple
