Note that this bridge puts the originating source address as bridged

destination address.

This does not matter for PDU2 type of PGN's (== PDU-specific is not the 
destination address), it may not be completely right.

I'd expect to 'empty' (== put J1939_NO_ADDR) the src_addr.can_addr.j1939.addr 
member before sendto(), resulting in a broadcasted PGN.

OK I hope I fixed that, I want to keep the originating source address and it 
should stay PDU2 type.

In a later iteration, You could (if necessary, since I have no clue what kind
of traffic you will bridge):
* make the receiving socket (s) 'promiscuous', i.e. receiving all traffic.
* fetch the original destination by using recvmsg() as illustrated in jspy.

At the moment I am also not aware what particular traffic I will bridge, I am
still 'playing' around. But the target is to place that bridge between an 
existing engine bus and an existing ECU. So different source address' the 
existing ECU is 'interested' in (but I think not in all in the network) and one 
source address from the ECU.

In the example below, I wanted, if the pgn is 0xFEF5 (this is a pgn I will 
definitely need) to print the first byte otherwise just bridge it. 
But it is not working! Could you see an error? Sorry!

int main (void)
{
	int s;
	s = socket(PF_CAN, SOCK_DGRAM, CAN_J1939);
	    
	struct sockaddr_can addr;

    memset(&addr, 0, sizeof(addr));
    addr.can_ifindex = if_nametoindex("can0");
    addr.can_addr.j1939.name = J1939_NO_NAME;    
    addr.can_addr.j1939.addr = 0x00;
    addr.can_addr.j1939.pgn = J1939_NO_PGN;
    addr.can_family = AF_CAN;  
   
   
    if (bind(s, (void *)&addr, sizeof(addr))<0)
    	{
    		perror ("bind failed");
        	}
        	
     
    int s2;
	s2 = socket(PF_CAN, SOCK_DGRAM, CAN_J1939);
	
	struct sockaddr_can addr2;	
	   
    memset(&addr2, 0, sizeof(addr2));
    addr2.can_ifindex = if_nametoindex("can1");
    addr2.can_addr.j1939.name = J1939_NO_NAME;    
    addr2.can_addr.j1939.addr = 0x3D;
    addr2.can_addr.j1939.pgn = J1939_NO_PGN;
    addr2.can_family = AF_CAN;     
   
    if (bind(s2, (void *)&addr2, sizeof(addr2))<0)
    	{
    		perror ("bind2 failed");
        	}
    int ret;
	socklen_t len; 
	struct sockaddr_can src_addr;
	char buf[128];


	while (1) {
		len = sizeof(src_addr);
		ret = recvfrom(s, buf, sizeof(buf), 0, (void *)&src_addr, &len);
		
		if (ret < 0)
		perror ("recvfrom failed");
		
		src_addr.can_addr.j1939.addr = J1939_NO_ADDR;

		/*if the frame is sent by 0x30 do this*/
		if (src_addr.can_addr.j1939.pgn == 0xFEF5)
		{
			if (ret < 0)
			perror ("no data");
			
			printf("%x\n", buf[0]);
/*I didn't get it what you wanted to tell me with the remainder*/
			
			if (sendto(s2, buf, ret, 0, (void *)&src_addr, len) < 0)
				perror("sendto failed");
						
		}
		
		/*else just bridge it*/
		else
		{ 
			if (sendto(s2, buf, ret, 0, (void *)&src_addr, len) < 0)
				perror("sendto failed");
		}

	}

  		 
  return 0;
}



--Wolfgang