[Bluez-devel] Problem with read on RFCOMM Sockets

[Bluez-devel] Problem with read on RFCOMM Sockets

[ionut dediu]

Hy
I have a Fedora linux running kernel 2.6.5-1.358. I
made a simple client program on the PC which reads
data sent from a Phone Server application through
rfcomm. Read allways returns the correct no of bytes,
but the buffer in which I read allways has just 1 byte
of data. I saw from another post that there were
similar problems with rfcomm sockets, and as I
understand this could be a kernel bug. Could you tell
me what upgrade should I make to the kernel ? Thanks a
lot in advance.

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Re: [Bluez-devel] Problem with read on RFCOMM Sockets

[Marcel Holtmann]

Hi,

> I have a Fedora linux running kernel 2.6.5-1.358. I
> made a simple client program on the PC which reads
> data sent from a Phone Server application through
> rfcomm. Read allways returns the correct no of bytes,
> but the buffer in which I read allways has just 1 byte
> of data. I saw from another post that there were
> similar problems with rfcomm sockets, and as I
> understand this could be a kernel bug. Could you tell
> me what upgrade should I make to the kernel ?

show us your source code.

Regards

Marcel




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Re: [Bluez-devel] Problem with read on RFCOMM Sockets

[ionut dediu]

Hi

Here is the source code. For testing the receiving of
data I tried commenting the select loop, and do just
receiveData, and I get the same results: read returns
the correct number of bytes, but in the buffer is
copied just one byte of data. Please tell me if I'm
doing smth wrong. Thanks a lot.

#include <unistd.h>
#include <syslog.h>
#include <errno.h>
#include <stdlib.h>
#include <string.h>
#include <stdio.h>

#include <sys/types.h>
#include <sys/socket.h>
#include <sys/select.h>

#include <bluetooth/bluetooth.h>
#include <bluetooth/rfcomm.h>

#define BT_LOCAL_ADDR "00:0C:76:D3:4C:D3"
#define BT_REM_NOKIA_ADDR "00:60:57:D2:27:66"

#define DIM 256
#define STDIN 0
#define STDOUT 1

char userBuf[DIM];
char remoteBuf[DIM];

int clientSocket = 0;

int do_connect(char * remAddr)
{
	struct sockaddr_rc rem_addr, loc_addr;
	int s;

	if ((s = socket(PF_BLUETOOTH, SOCK_STREAM,
BTPROTO_RFCOMM)) < 0) {
		syslog(LOG_ERR, "Can't create socket. %s(%d)",
strerror(errno), errno);
		return -1;
	}

	memset(&loc_addr, 0, sizeof(loc_addr));
	loc_addr.rc_family = AF_BLUETOOTH;
	str2ba(BT_LOCAL_ADDR, &loc_addr.rc_bdaddr);
	if (bind(s, (struct sockaddr *) &loc_addr,
sizeof(loc_addr)) < 0) {
		printf("Can't bind socket. %s(%d)", strerror(errno),
errno);
		exit(1);
	}

	memset(&rem_addr, 0, sizeof(rem_addr));
	rem_addr.rc_family = AF_BLUETOOTH;
	baswap(&rem_addr.rc_bdaddr, strtoba(remAddr));
	rem_addr.rc_channel = 4;
	if (connect(s, (struct sockaddr *)&rem_addr,
sizeof(rem_addr)) < 0 ) {
		printf("Can't connect. %s(%d)\n", strerror(errno),
errno);
		close(s);
		return -1;
	}

	printf("Connected\n");

	return s;

}

int receiveData()
{
	int noBytesRead = 0;
	memset(remoteBuf, 0, DIM);
	noBytesRead = read(clientSocket, remoteBuf, DIM);
	if(noBytesRead == -1)
	{
		printf("Can't read. %s(%d)\n", strerror(errno),
errno);
		exit(-1);
	}
	if(noBytesRead == 0)
	{
		printf("Disconnected\n");
		exit(0);
	}
	printf("REMOTE[%d](strlen = %d) : %s\n", noBytesRead,
strlen(remoteBuf), remoteBuf);
	return noBytesRead;
//	write(STDOUT, buf, strlen(buf));
}

int sendData()
{
	memset(userBuf, 0, DIM);
	read(STDIN, userBuf, DIM);
	if(write(clientSocket, userBuf, strlen(userBuf)) !=
strlen(userBuf))
	{
		printf("Can't write. %s(%d)\n", strerror(errno),
errno);
		return -1;
	}
	return 0;
}

int main(int argc, char** argv)
{
	fd_set read_fds;	//fd_set used in select()
	fd_set tmp_fds;		//fd_set temporary fds
	int fdmax;		//maximum no of file descriptors
	int i = 0;

	clientSocket = do_connect(BT_REM_NOKIA_ADDR);
	FD_SET(clientSocket, &read_fds);
	FD_SET(STDIN, &read_fds);
	fdmax = clientSocket;
/*	while(1)
	{
		receiveData();
	}*/
	// main loop
	while(1)
	{
		tmp_fds = read_fds;
		if(select(fdmax + 1, &tmp_fds, NULL, NULL, NULL) ==
-1)
		{
			printf("ERROR in select. %s(%d)\n",
strerror(errno), errno);
			exit(errno);
		}
		else
		{
			for(i = 0; i <= fdmax; i++)
			{
				if(FD_ISSET(i, &tmp_fds))
				{
					// received data from the bluetooth end point
		    			if(i == clientSocket)
					{
						receiveData();
					}
					// received input data from the user
					if(i == STDIN)
					{
						sendData();
					}
				}
			}
		}
	}

	close (clientSocket);
	return 0;
}




	
		
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Re: [Bluez-devel] Problem with read on RFCOMM Sockets

[Marcel Holtmann]

Hi,

> Here is the source code. For testing the receiving of
> data I tried commenting the select loop, and do just
> receiveData, and I get the same results: read returns
> the correct number of bytes, but in the buffer is
> copied just one byte of data. Please tell me if I'm
> doing smth wrong. Thanks a lot.

your buffer should be "unsigned char" and you shouldn't use strlen() to
check to length of your buffer. Rely on the return value of read().

Regards

Marcel




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RE: [Bluez-devel] Problem with read on RFCOMM Sockets

[Williams, Richard]

I understand why strlen should not be used in this case, but why
unsigned char instead of char ? There are many examples of the=20
use of the generic file I/O read() function in the literature=20
using char buffers. Is this case different ?

thanks, Best regards,

Rich

Hi,

> Here is the source code. For testing the receiving of
> data I tried commenting the select loop, and do just
> receiveData, and I get the same results: read returns
> the correct number of bytes, but in the buffer is
> copied just one byte of data. Please tell me if I'm
> doing smth wrong. Thanks a lot.

your buffer should be "unsigned char" and you shouldn't use strlen() to
check to length of your buffer. Rely on the return value of read().

Regards

Marcel




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RE: [Bluez-devel] Problem with read on RFCOMM Sockets

[Marcel Holtmann]

Hi Richard,

> I understand why strlen should not be used in this case, but why
> unsigned char instead of char ? There are many examples of the 
> use of the generic file I/O read() function in the literature 
> using char buffers. Is this case different ?

it actually depends on the other side. If the other side also uses char
then there should be no problem, but it is better to use unsigned char
if you don't know what the other side is sending.

Regards

Marcel




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