Thread: [sockets] Finding out if a browser client disconnected

Hello!
This is currently my biggest problem with the chatserver. I need to find out if a client is still connected so I can free up the slot and close the connection when a client leaves.
Every connected client goes into a loop, constantly writing new stuff to the socket (the browser) which is the chat stream. Unfortunatly the "write" function I use to do this never returns -1, even if the browser already closed the connection so I have no way to find ouy if it's still there and receiving.
The code looks like this:

Code:

	while(connected) {
		// check the buffer for new text to send
		if (strlen(chatter[myid].buffer) > 0) {
			sprintf(sendbuf, "%s", chatter[myid].buffer);
			sprintf(chatter[myid].buffer, "");
			if(write(sock, sendbuf, strlen(sendbuf)) == -1)
				connected = 0; // never ever happens
			} 
		}
		sleep(1);
	}

So out of couriousity I tried what happens when I read() from the browser just as a test if it's still there:

Code:

	while(connected) {
		// read something from the browser, just as a test...
		if(read(sock, NULL, 1) == -1)
			fprintf(stderr, "party! we are disconnected\n");
		else
			fprintf(stderr, "still connected :/\n");

		sleep(1);
	}

This shows me that it _could_ work, because what happens is, that the function stops there at the read, waiting for the browser to actually send 1 char. Of course it doesn't. But when I close the connection from the browser now, it returns -1 and detects that it's disconnected! It doesn't work when I try to read 0 chars.
There _has_ to be a way to find out if the browser is still connected. :/ Please help cause I'm lost.

You can tell then the client is gone, because recv will return zero.

Have you researched the select() function? If not, have a look in this document.

Basically, you can put file descriptors into a special struct array, and select will tell you if there's any data to be read from them. If it says there is, and when you do the recv and get zero bytes, this means the client has disconnected.

Beej is your friend.

Use 'select', and the FD_ macros to test sockets for read/write availability.

Quzah.

Originally posted by Hammer
You can tell then the client is gone, because recv will return zero.

Have you researched the select() function? If not, have a look in this document.

Basically, you can put file descriptors into a special struct array, and select will tell you if there's any data to be read from them. If it says there is, and when you do the recv and get zero bytes, this means the client has disconnected.

Ah, beat me to it. That's what happens when you talk on the phone while typing a reply.

Quzah.