Eiko Oltmanns schrieb:
Hi!
I have a problem, with reading from rfcomm sockets. I wrote a little
client application, that connects to an other device and just prints
all received data. I want to receive data as soon as it is sent from
the remove device. The problem is, that the read function blocks,
until 4k of data are sent on the remote side, although the number of
requested bytes passed to read is much lower. Then read starts to read
out the received data. When all data has been read, the next call
again blocks until the next 4 kb are available.
Distribution: Debian, "Lenny"
Kernelversion: 2.6.26-13
Bluez-libs: 3.36-1
Bluez-utils: 3.36-3
Here is the minimal code, which reproduces my problem:
int main(int argc, char **argv)
{
int sock = hci_open_dev( devId );
if ( sock < 0 ) return -1;
int rfcommSocket = socket(AF_BLUETOOTH, SOCK_STREAM, BTPROTO_RFCOMM);
if ( rfcommSocket < 0 ) return -1;
struct sockaddr_rc addr;
addr.rc_family = AF_BLUETOOTH;
addr.rc_channel = channel;
str2ba("00:09:DD:50:72:0F", &addr.rc_bdaddr );
// connect to server
int status = connect(rfcommSocket, (struct sockaddr *)&addr,
sizeof(addr));
if ( status < 0 ) rerurn - 1;
int bytes = write(rfcommSocket,"Test",4); /* works as expected.
Data is received immediately by the remote device */
if ( bytes != 4 ) return - 1; //tested only for 4 for simplicity
while (1) {
unsigned char buf[10]; /* the buf size seems to have no
influence on my problem */
memset( buf, 0, sizeof(buf));
int bytes = read(rfcommSocket, buf, sizeof(buf)-1); /* blocks
until 4k of data are available */
if ( bytes > 0 )
cout << buf;
if ( bytes < 0 )
{
return -1;
}
}
return 0;
}
Greetings,
Eiko
I think my code should be correct, isn't it? Is there maybe an option in
the kernel config, that could cause such a behaviour of the socket? I am
running a self configured kernel on an embedded hardware. Any other
suggestions?
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