Thread: Blocking Sockets Issue

Hey there,
I've had this problem for a little bit, and it is now time to track it down, as its become obscenely troublesome.

Premise:
I am using sockets under WinSock2 to retrieve an XML page and parse it for use.

Problem:
My socket recv() call intermittently blocks indefinately. I cannot determine a pattern to when it decides its going to block forever, but I speculate it has to do with the response time of the server? There server is a off-site box that operates with (an average) of less than 50ms ping to the development box.

Details:

Code:

	if ( WSAStartup( MAKEWORD( 2, 2 ), &wsaData ) )
		return;
	if ( ( ConnectSocket = socket( AF_INET, SOCK_STREAM, IPPROTO_TCP ) ) == INVALID_SOCKET )
		return;
	if ( connect( ConnectSocket, (sockaddr *) &clientService, sizeof( clientService ) ) == SOCKET_ERROR )
		return;
	/* ... */
	send( ConnectSocket, outBuffer, strlen( outBuffer ), 0 );
	shutdown( ConnectSocket, 0x01 );
	do
	{
		bytes = recv( ConnectSocket, inBuffer, 1024, 0 );
		if ( bytes > 0 )
		{
			/* ... */
		}
		else if ( bytes < 0 )
		{
			Disconnect( );
			return WSAGetLastError( );
		}
		/* ... */
	} while ( bytes > 0 );
	/* ... */
	closesocket( ConnectSocket );
	WSACleanup( );

Originally Posted by Salem

Why are you doing shutdown() immediately after send, and BEFORE doing a recv ?

I am telling the socket that no more data is to be written to it.
shutdown Function (Windows)

Originally Posted by Salem

How are outBuffer and inBuffer declared?

One's a fixed array 1024, the other is a char* pointer of variable length depending on the length of the data I'm sending /out/.

Both operate as expected under run conditions.

Originally Posted by Salem

Do you attempt to add a \0 to inBuffer, even though it may be full. Doing so seems like a buffer overflow if you have char inBuffer[1024];

inBuffer operates as expected under run conditions.

My issue is recv() intermittantly decides to block forever, my assumption is that its based on the response time of the server, but I have no data to correlate to that (and correlation does not imply causation, anyway).

Please post back with any ideas you may have

Thanks

Originally Posted by Salem

So you DO have a buffer of 1024.
And if you receive 1024 characters and do inBuffer[bytes] = '\0' to make it a string, you HAVE A BUFFER OVERFLOW.

Where does that \0 go? Is that the cause of your problems?

Sorry, I should have made it clear that I am not null terminating the string; I don't think recv() would write past the 1024 limit I specified? I do not have much experience with Sockets; The rest of the language I have a fair grip on

This is not the error I'm looking for

How do you bind to the socket? I'm pretty sure that if you don't specify the socket as non-blocking then recv() is going to block when there is no data to receive. That's how it works.

Oi. This is embarassing, the problem [seems] to be resolved. By some bizzare twist of logic the code I had written was *ahem* poorly interacting with other code I wrote, causing the socket to open and close a couple hundred times a second.

Resolved it when I was mucking about with binding (which doesn't seem to be needed if the connection being established is a client and not a server? or something?)

Anyway, thank you guys for your help, you helped me arrive at the solution

Regards,
Teeg

You need to bind to a socket if you are going to listen on it.