TCP-Socket.receive does not return. Why?

[Marc from D]

Hi!
Globally defined:
CSocket sock;

In a function:
TRACE("\r\nTCPRead before sock.Receive");
temp = sock.Receive(IBuf,64);
TRACE("\r\nTCPRead after sock.Receive");

in InitInstance:
AfxSocketInit(&WsaData);

Doing this the Receive-function never returns. Any hint?


Thanks a lot!

Marc

[wildfrog]

If you're using blocking sockets the Receive call will wait until 1 or more bytes are read (socket is closed or an error occurs).

- petter

[Viorel]

Maybe no one sends data to that socket?

[Marc from D]

OK: I even expect that no one sends a byte. But in this case there should be a timout?
How can I make the function waiting only a certain time?

But already you helped me!

Thanks!

Marc

[wildfrog]

You should take a look at non-blocking or asynchronous sockets. CAsyncSocket is one solution.

- petter

[philkr]

Indeed you should use CASyncSocket or the WinSock API, because there are some problems with CSocket (though not in your example), because it tries to emulate blocking using a non-blocking socket. I don't know why most network programming beginners use CSocket. Maybe because of bad tutorials?

[Viorel]

How can I make the function waiting only a certain time?

I think this can be done with select function:

long ms = ... // timeout in milliseconds
SOCKET s = sock;
fd_set set;
FD_ZERO(&set);
FD_SET(s, &set);
timeval timeout;
timeout.tv_sec = ms / 1000;
timeout.tv_usec = (ms % 1000) * 1000;
int const r = select(((int)s) + 1, &set, 000, 000, &timeout);

switch(r)
{
case 0:
    // timeout
    break;
case 1:
    // OK. Data available
    break;
default:
    // Error
}

I hope it helps.

[MikeAThon]

OK: I even expect that no one sends a byte. But in this case there should be a timout?
How can I make the function waiting only a certain time?

Changing to raw winsock API calls, or to CAsyncSocket, will add to the complexity of your program.

If all you want is a CSocket with a timeout, then see the CTimeoutScoket class in this MSDN article: "How To Configure a Time-Out on a CSocket Operation" at http://support.microsoft.com/kb/q138692/

The class is very short. It extends CSocket functionality by adding two public functions ( SetTimeOut and KillTimeOut ) and one protected function ( OnMessagePending ).

Mike

[henky@nok.co.id]

OK: I even expect that no one sends a byte. But in this case there should be a timout?
How can I make the function waiting only a certain time?

But already you helped me!

Thanks!

Marc

You can use non-blocking socket.
There are 2 ways to realize non-blocking socket:
1. Using setsockopt() function to set timeout of read/write operation.
Note: According to MSDN, SO_RCVTIMEO and SO_SNDTIMEO are not
supported in CAsyncSocket.SetSockOpt().
2. Using timer to stop blocking.

If you make a program using MFC, you can use CAsyncSocket and
overwrite event handler OnReceive()/OnSend() to read/write data.