RFCOMM server multiple client connections

RFCOMM server multiple client connections

[Kasper Revsbech]

Hi everyone.
I am trying do do a simple client server setup  with bluez.
I can manage to have a client and a server on rfcomm sockets where the 
server listen on a socket and accept a connection from the client by 
connect. But then if I set the server back to accepting without putting 
down the one client connection it doesn't accept a new connection.
When I read thought the documentation I can find on Bluez and Bluetooth 
in general it seems like it should be possible to multiplex serveal 
virtual rfcomm connections  on one actual connection. But however I 
really can get it working and can't find any code where they do 
something similar.

Hope that someone can give me a hint...

/Kasper Revsbech


Here is a example of what I have tried to make it work:

Client:
--------------------------

#include <stdio.h>
#include <unistd.h>
#include <sys/socket.h>
#include <arpa/inet.h>
#include <bluetooth/bluetooth.h>
#include <bluetooth/rfcomm.h>
#define number_of_connections 5

int main(int argc, char **argv)
{
 
  struct sockaddr_rc addr = { 0 };
  int s[number_of_connections], status, getpeer_status;
    char dest[18] = "00:11:67:05:4f:dc";
    struct sockaddr peer_address;
    int namelen = sizeof(peer_address),i;

    // set the connection parameters (who to connect to)
    addr.rc_family = AF_BLUETOOTH;
    addr.rc_channel = (uint8_t) 1;
    str2ba( dest, &addr.rc_bdaddr );
   
for (i=0 ;i=(number_of_connections-1);i++){
   
      s[i] = socket(AF_BLUETOOTH, SOCK_STREAM, BTPROTO_RFCOMM);

  
     /*connect to server*/
      status = connect(s[i], (struct sockaddr *)&addr, sizeof(addr));
   
   
    // send a message
    if( status == 0 ) {
      status = write(s[i], "hello!", 6);
    }

    if( status < 0 ) perror("uh oh");
    }
  



    for (i=0 ;i=(number_of_connections-1);i++){
      close(s[i]);
    }  

    return 0;
}

-----------------------------------
Server:
-----------------------------------
#include <stdio.h>
#include <unistd.h>
#include <sys/socket.h>
#include <bluetooth/bluetooth.h>
#include <bluetooth/rfcomm.h>
#define number_of_connections 5

int main(int argc, char **argv)
{
    struct sockaddr_rc loc_addr = { 0 }, rem_addr = { 0 };
    char buf[1024] = { 0 };
    int s, client[number_of_connections], bytes_read;
    socklen_t opt = sizeof(rem_addr);
    int i;
    // allocate socket
    s = socket(AF_BLUETOOTH, SOCK_STREAM, BTPROTO_RFCOMM);

    // bind socket to port 1 of the first available
    // local bluetooth adapter
    loc_addr.rc_family = AF_BLUETOOTH;
    loc_addr.rc_bdaddr = *BDADDR_ANY;
    loc_addr.rc_channel = (uint8_t) 1;
    bind(s, (struct sockaddr *)&loc_addr, sizeof(loc_addr));

    // put socket into listening mode
    listen(s, number_of_connections);
    for (i=0 ;i=(number_of_connections-1);i++){

    // accept one connection
      client[i] = accept(s, (struct sockaddr *)&rem_addr, &opt);

      ba2str( &rem_addr.rc_bdaddr, buf );
      fprintf(stderr, "accepted connection from %s\n", buf);
      memset(buf, 0, sizeof(buf));

      // read data from the client
      bytes_read = read(client[i], buf, sizeof(buf));
      if( bytes_read > 0 ) {
        printf("received [%s]\n", buf);
      }
    }
   
    // close connection
      for (i=0 ;i=(number_of_connections-1);i++){
       close(client[i]);
     }
     close(s);
    return 0;

Re: RFCOMM server multiple client connections

[Marcel Holtmann]

Hi Kasper,

> I am trying do do a simple client server setup  with bluez.
> I can manage to have a client and a server on rfcomm sockets where the 
> server listen on a socket and accept a connection from the client by 
> connect. But then if I set the server back to accepting without putting 
> down the one client connection it doesn't accept a new connection.
> When I read thought the documentation I can find on Bluez and Bluetooth 
> in general it seems like it should be possible to multiplex serveal 
> virtual rfcomm connections  on one actual connection. But however I 
> really can get it working and can't find any code where they do 
> something similar.

are the clients running on multiple adapters. If they run on the same
adapter, it won't work. RFCOMM is not a layer that assign dynamic
channels numbers to each connection (like L2CAP does) and thus once a
RFCOMM channel is in use (the pair is bdaddr:channel) then you can
connect to it twice.

Regards

Marcel

Re: RFCOMM server multiple client connections

[Kasper Revsbech]

Marcel Holtmann skrev:
> Hi Kasper,
>
>   
>> I am trying do do a simple client server setup  with bluez.
>> I can manage to have a client and a server on rfcomm sockets where the 
>> server listen on a socket and accept a connection from the client by 
>> connect. But then if I set the server back to accepting without putting 
>> down the one client connection it doesn't accept a new connection.
>> When I read thought the documentation I can find on Bluez and Bluetooth 
>> in general it seems like it should be possible to multiplex serveal 
>> virtual rfcomm connections  on one actual connection. But however I 
>> really can get it working and can't find any code where they do 
>> something similar.
>>     
>
> are the clients running on multiple adapters.If they run on the sameadapter, it won't work. RFCOMM is not a layer that assign dynamic
> channels numbers to each connection (like L2CAP does) and thus once a
> RFCOMM channel is in use (the pair is bdaddr:channel) then you can
> connect to it twice.
>
>   
Exactly the client sockets are all originated from the same adapter. 
What I want to do is by some libsocks tricks to emulate a native tcp/ip 
socket and provide nearly the same interface. So far I have been using 
RFCOMM. As I understand you, this setup with multiple sockets 
connections from each host is possible using a l2cap socket instead. 
Which leads into the next question. Reading documentation on Bluetooth 
stacks in general some seems to provide a SOCK_STREAM type using l2cap. 
However this does not seems to be the case in the Bluez stack. So is 
there a way to have a somehow reliable stream connection  allowing 
multiple connections from each host?

Regards and thanks a lot

Kasper Revsbech

Re: RFCOMM server multiple client connections

[Marcel Holtmann]

Hi Kasper,

>>> I am trying do do a simple client server setup  with bluez.
>>> I can manage to have a client and a server on rfcomm sockets where  
>>> the server listen on a socket and accept a connection from the  
>>> client by connect. But then if I set the server back to accepting  
>>> without putting down the one client connection it doesn't accept a  
>>> new connection.
>>> When I read thought the documentation I can find on Bluez and  
>>> Bluetooth in general it seems like it should be possible to  
>>> multiplex serveal virtual rfcomm connections  on one actual  
>>> connection. But however I really can get it working and can't find  
>>> any code where they do something similar.
>>>
>>
>> are the clients running on multiple adapters.If they run on the  
>> sameadapter, it won't work. RFCOMM is not a layer that assign dynamic
>> channels numbers to each connection (like L2CAP does) and thus once a
>> RFCOMM channel is in use (the pair is bdaddr:channel) then you can
>> connect to it twice.
>>
>>
> Exactly the client sockets are all originated from the same adapter.  
> What I want to do is by some libsocks tricks to emulate a native tcp/ 
> ip socket and provide nearly the same interface. So far I have been  
> using RFCOMM. As I understand you, this setup with multiple sockets  
> connections from each host is possible using a l2cap socket instead.  
> Which leads into the next question. Reading documentation on  
> Bluetooth stacks in general some seems to provide a SOCK_STREAM type  
> using l2cap. However this does not seems to be the case in the Bluez  
> stack. So is there a way to have a somehow reliable stream  
> connection  allowing multiple connections from each host?

RFCOMM is SOCK_STREAM and L2CAP is SOCK_SEQPACKET. If someone  
implements L2CAP retransmission and flow-control we could have  
SOCK_STREAM for L2CAP, too.

Regards

Marcel