Re: [Bluez-devel] reading response on bluetooth socket

[Marcel Holtmann <marcel@holtmann.org>]

Hi Goetz,

> After having set up a rfcommm connection from my notebook to a mobile phone I 
> need to get the response data from the mobile device. I can read from the 
> socket using 'recv()' but if no data is there at thaht moment this will block 
> the process or pause my program. What I need to do is get a signal on 'data 
> available' on the socket for reading or a non blocking read. I heard there is 
> a function 'select()' .. but it does not seem to work or I don't understand 
> it. It needs to be as simple as possible.
> 
> This is what I have now:
> 
> // init + declare variables
> 	fd_set readFds;
> 	struct timeval timeout;
>     	struct sockaddr_rc addr = { 0 };

don't do this. Use memset() instead.

>    	int rfcomm_sock, status; 
> 	
> // allocate a socket
>    	 rfcomm_sock = socket(AF_BLUETOOTH, SOCK_STREAM, BTPROTO_RFCOMM);
> 
> // set the connection parameters (who to connect to)
>     	addr.rc_family = AF_BLUETOOTH;
>     	addr.rc_channel = (uint8_t) dest_channel;

Why do you cast here. No need in doing this. Get you declarations right.

>     	str2ba( dest, &addr.rc_bdaddr );
> 
> // connect to server, here mobile phone
>    	 status = connect(rfcomm_sock, (struct sockaddr *)&addr, sizeof(addr));
> 
> 	timeout.tv_sec=5;
> 	timeout.tv_usec=0;	
> 	FD_ZERO(&readFds);
> 	FD_SET(rfcomm_socket, &readFds);

What is it? rfcomm_sock, rfcomm_socket or rfcommsocket. Get your code
clean.

> 	if (select(rfcommsocket + 1, &readFds, NULL, NULL, &timeout) == 0) 
> 	{
> 		printf("timed out");
> 	}
> 	else
> 		printf("data ready for read");

And you should check the manual page of select() or move over using
poll(). This might be a better example:

        while (1) {
                fd_set rset;

                FD_ZERO(&rset);
                FD_SET(sk, &rset);

                if (select(sk + 1, &rset, NULL, NULL, NULL) < 0)
                        break;

                if (!FD_ISSET(sk, &rset))
                        continue;

                ...
        }

Regards

Marcel



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