2 replies to this topic

[leblebi]

First of all, hi to everybody. Nice place you got here.

If you have some UDP experience you probably already understood my problem:

I have a server and a number of clients connected to it(logically connected since this is using UDP). Server has only one socket/port and sends data out of this port to all of the clients. If for some reason one of the clients disconnect un-gracefully(e.g. Ctrl-C, End Process, etc.) the recvfrom() command returns a WSAECONNRESET(yes I read about it, the reason is ICMP). This isn't a problem on its own but the real problem is that the server fails to receive further packets from clients.

From what I google'd so far it seems at some point even Serious Sam suffered from this, there is an article on a pixelate mag that specifically points out this error code, a Win2K fix, and a bunch of confused people posting at various forums.

I looked at the Q3 code and no special care is taken to handle this situation, although I use the exact same socket creation and configuration code.

My current fix is when I get a WSAECONNRESET, I label that client as dead and remove it. This fixes the problem. But I feel a little uneasy about that solution since Q3 does not use such a failsafe for this.

Can anyone offer any help on this issue?

[.oisyn]

I did some network code for a game a few years ago, of course we also used UDP but I don't think we did anything with the WSAECONNRESET error... I think I have the source somewhere, I'll take a look at it.

But what I don't understand is why the server shouldn't receive any more messages. But you could try to reinitialize the socket and continue sending/receiving, although that might fuck up the current receive buffer... (but then again, that buffer isn't going to be of much use if you're not able to read it anyway)

[leblebi]

I found the reason and the fix to the problem.

If you have a non-blocking recvfrom() loop like this to read from your socket, you are doing the wrong thing:

do

{

  ret = recvfrom(...);

  if ( ret != SOCKET_ERROR )

    dispatch_data ();

}while ( ret != SOCKET_ERROR )

Because WSAECONNRESET obviously causes a SOCKET_ERROR but actually there is no error and you should keep reading the socket when WSAECONNRESET occurs. So it should read something like this;

do

{

  ret = recvfrom(...);

  if ( ret == SOCKET_ERROR )

    err = WSAGetLastError ( );

  else

    dispatch_data ();

}while ( ret != SOCKET_ERROR || ( ret == SOCKET_ERROR && err == WSAECONNRESET ) )

It turns out that Q3 is actually handling this issue like this. It also includes the WSAWOULDBLOCK as an OK to read error.