Question on simple RFCOMM server

Question on simple RFCOMM server

[Mateus Interciso]

Hello, I have a very simple RFCOMM server that I adapted from an 
extremely simple TCP echo server I've made for learning TCP, it's a 
simple fork() server, and while the TCP server works perfeclty, the 
RFCOMM works only with 2 connected clients at the same time, and I'm 
failling to see the problem, can someone help me?

Here's the code:

(The commented part if the TCP part)

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <errno.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <sys/wait.h>
#include <bluetooth/bluetooth.h>
#include <bluetooth/rfcomm.h>

#define MYPORT 10
#define BACKLOG 31
#define MAX_SIZE 80

int main(int argc, char *argv[])
{
   int listenfd, connfd;
   pid_t childpid;
   socklen_t clilen;
   struct sockaddr_rc cliaddr, servaddr;
   char buf[MAX_SIZE];
   int i =0;

   //listenfd = socket(AF_INET, SOCK_STREAM, 0);
   listenfd = socket(AF_BLUETOOTH, SOCK_STREAM, BTPROTO_RFCOMM);
   if(listenfd < 0)
   {
     perror("socket");
     exit(errno);
   }

   bzero(&servaddr, sizeof(servaddr));
   servaddr.rc_family = AF_BLUETOOTH;
   servaddr.rc_bdaddr = *BDADDR_ANY;
   servaddr.rc_channel = (uint8_t)MYPORT;
   /*
   servaddr.sin_family = AF_INET;
   servaddr.sin_addr.s_addr = htonl(INADDR_ANY);
   servaddr.sin_port = htons(MYPORT);
   */
   if(bind(listenfd,(struct sockaddr*)&servaddr, sizeof(servaddr)) < 0)
   {
     perror("bind");
     exit(errno);
   }

   if(listen(listenfd,BACKLOG) < 0)
   {
     perror("listen");
     exit(errno);
   }

   while(1)
   {
     clilen = sizeof(cliaddr);
     if((connfd = accept(listenfd, (struct sockaddr*)&cliaddr, &clilen)) 
< 0)
     {
       perror("accept");
       exit(errno);
     }
     if((childpid = fork()) == 0)
     {
       i = 0;
       close(listenfd);
       fprintf(stderr,"[DEBUG] Got connection\n");
       memset(buf,'\0',sizeof(buf));
       //echo server
       if(read(connfd, buf, MAX_SIZE) < 0) perror("read");
       else
         if(send(connfd, buf, strlen(buf), 0) < 0) perror("send");
       exit(0);
     }
     close(connfd);
   }
   return 0;
}


Thanks.

Re: Question on simple RFCOMM server

[Peter Wippich]

Hi Mateus,

I don't think the problem is with your code but has something to do with 
the Bluetooth Master / Slave mode. By default for the RFCOMM connection 
opened by the remote device your server is a Bluetooth Slave. And as a 
slave you can not handle more than 2 connections at once. To allow more 
connections you need your server to do a role switch after connection 
setup. Than it will act as a master and can handle up to seven 
connections. 

Ciao, 

Peter

On Tue, 25 Aug 2009, Mateus Interciso wrote:

> Hello, I have a very simple RFCOMM server that I adapted from an extremely
> simple TCP echo server I've made for learning TCP, it's a simple fork()
> server, and while the TCP server works perfeclty, the RFCOMM works only with 2
> connected clients at the same time, and I'm failling to see the problem, can
> someone help me?
> 
> Here's the code:
> 
> (The commented part if the TCP part)
> 
> #include <stdio.h>
> #include <stdlib.h>
> #include <unistd.h>
> #include <string.h>
> #include <errno.h>
> #include <sys/types.h>
> #include <sys/socket.h>
> #include <netinet/in.h>
> #include <arpa/inet.h>
> #include <sys/wait.h>
> #include <bluetooth/bluetooth.h>
> #include <bluetooth/rfcomm.h>
> 
> #define MYPORT 10
> #define BACKLOG 31
> #define MAX_SIZE 80
> 
> int main(int argc, char *argv[])
> {
>   int listenfd, connfd;
>   pid_t childpid;
>   socklen_t clilen;
>   struct sockaddr_rc cliaddr, servaddr;
>   char buf[MAX_SIZE];
>   int i =0;
> 
>   //listenfd = socket(AF_INET, SOCK_STREAM, 0);
>   listenfd = socket(AF_BLUETOOTH, SOCK_STREAM, BTPROTO_RFCOMM);
>   if(listenfd < 0)
>   {
>     perror("socket");
>     exit(errno);
>   }
> 
>   bzero(&servaddr, sizeof(servaddr));
>   servaddr.rc_family = AF_BLUETOOTH;
>   servaddr.rc_bdaddr = *BDADDR_ANY;
>   servaddr.rc_channel = (uint8_t)MYPORT;
>   /*
>   servaddr.sin_family = AF_INET;
>   servaddr.sin_addr.s_addr = htonl(INADDR_ANY);
>   servaddr.sin_port = htons(MYPORT);
>   */
>   if(bind(listenfd,(struct sockaddr*)&servaddr, sizeof(servaddr)) < 0)
>   {
>     perror("bind");
>     exit(errno);
>   }
> 
>   if(listen(listenfd,BACKLOG) < 0)
>   {
>     perror("listen");
>     exit(errno);
>   }
> 
>   while(1)
>   {
>     clilen = sizeof(cliaddr);
>     if((connfd = accept(listenfd, (struct sockaddr*)&cliaddr, &clilen)) 
> < 0)
>     {
>       perror("accept");
>       exit(errno);
>     }
>     if((childpid = fork()) == 0)
>     {
>       i = 0;
>       close(listenfd);
>       fprintf(stderr,"[DEBUG] Got connection\n");
>       memset(buf,'\0',sizeof(buf));
>       //echo server
>       if(read(connfd, buf, MAX_SIZE) < 0) perror("read");
>       else
>         if(send(connfd, buf, strlen(buf), 0) < 0) perror("send");
>       exit(0);
>     }
>     close(connfd);
>   }
>   return 0;
> }
> 
> 
> Thanks.
> --
> To unsubscribe from this list: send the line "unsubscribe linux-bluetooth" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html
> 


|       Peter Wippich                   Voice: +49 30 46776411          |
|       G&W Instruments GmbH            fax:   +49 30 46776419          |
|       Gustav-Meyer-Allee 25, Geb. 12  Email: pewi@gw-instruments.de   |
|       D-13355 Berlin  / Germany                                       |

Re: Question on simple RFCOMM server

[Iain Hibbert]

On Tue, 25 Aug 2009, Mateus Interciso wrote:

> Hello, I have a very simple RFCOMM server that I adapted from an extremely
> simple TCP echo server I've made for learning TCP, it's a simple fork()
> server, and while the TCP server works perfeclty, the RFCOMM works only with 2
> connected clients at the same time, and I'm failling to see the problem, can
> someone help me?

You didn't post what the 'failure' was but for RFCOMM you can only have
one connection on a server channel (each RFCOMM channel corresponds to
an emulated serial port).

since a TCP connection is defined by the address and port at each end, the
Bluetooth equivalent is more likely to be a a L2CAP connection to a given
PSM which can support up to ~64k channels (though as the Peter Wippich
notes, the number of devices the radio can maintain connections with is
limited)

iain

Re: Question on simple RFCOMM server

[Mateus Interciso]

Thank you, however the Peter solution (setting via ioctl) worked 
perfectly, and it fit's with what I need, since all the clients are 
already implemented via RFCOMM, I'll leave it like this for now, the 
only issue is having to run it as root for setting the link mode, but I 
can bypass this by using hciconfig before running the main server.
Or is there any configuration that can make a normal user change the 
default link mode?

Thanks all once again.

Iain Hibbert wrote:
> On Tue, 25 Aug 2009, Mateus Interciso wrote:
> 
>> Hello, I have a very simple RFCOMM server that I adapted from an extremely
>> simple TCP echo server I've made for learning TCP, it's a simple fork()
>> server, and while the TCP server works perfeclty, the RFCOMM works only with 2
>> connected clients at the same time, and I'm failling to see the problem, can
>> someone help me?
> 
> You didn't post what the 'failure' was but for RFCOMM you can only have
> one connection on a server channel (each RFCOMM channel corresponds to
> an emulated serial port).
> 
> since a TCP connection is defined by the address and port at each end, the
> Bluetooth equivalent is more likely to be a a L2CAP connection to a given
> PSM which can support up to ~64k channels (though as the Peter Wippich
> notes, the number of devices the radio can maintain connections with is
> limited)
> 
> iain
> 
> 
> 

Re: Question on simple RFCOMM server

[Iain Hibbert]

On Tue, 25 Aug 2009, Mateus Interciso wrote:

> Or is there any configuration that can make a normal user change the default
> link mode?

yes - do

	int opt = RFCOMM_LM_MASTER;
	setsockopt(listend, SOL_RFCOMM, RFCOMM_LM, &opt, sizeof(opt));

before listen()

iain