I'm trying to create a Bluetooth connection from a Raspberry Pi 3B (Debian Linux) to an Android app. My problem is that the the Android framework (AFAIK) requires use of a UUID, e.g. createRfcommSocketToServiceRecord(UUID). Code excerpt:
// CREATE SPP SOCKET mSock = device.createRfcommSocketToServiceRecord( uuid ); if( mSock == null ) { return( -1 ); } // TRY TO CONNECT mSock.connect();
The code above works fine Android-to-Android.
Linux on the other hand requires just an "rc channel number" (an integer). The following is some sample code from MIT:
#include <stdio.h> #include <unistd.h> #include <sys/socket.h> #include <bluetooth/bluetooth.h> #include <bluetooth/rfcomm.h> int main(int argc, char **argv) { struct sockaddr_rc addr = { 0 }; int s, status; char dest[18] = "XX:XX:XX:XX:XX:XX"; // android address here // allocate a socket s = socket(AF_BLUETOOTH, SOCK_STREAM, BTPROTO_RFCOMM); // set the connection parameters (who to connect to) addr.rc_family = AF_BLUETOOTH; addr.rc_channel = (uint8_t) 1; str2ba( dest, &addr.rc_bdaddr ); // connect to server status = connect(s, (struct sockaddr *)&addr, sizeof(addr)); // send a message if( status == 0 ) { status = write(s, "hello!", 6); } if( status < 0 ) perror("uh oh"); close(s); return 0; }
I can't figure out how to bridge these two worlds.
Help!
I got SDP to work after a lot of hair-pulling. The code is below. It was fashioned after an example at https://people.csail.mit.edu/albert/bluez-intro/x604.html
This seems unnecessarily complicated to me. A case of "Computer Scientists Gone Wild!". For something as common and simple as this, they should have included a convenience wrapper.
// getchan - get channel for specified service // CONVENIENCE DEFINITIONS TO (IMHO) MAKE CODE MORE READABLE #define BYTE uint8_t #define UUID uuid_t #define LIST sdp_list_t #define SESSION sdp_session_t #define RECORD sdp_record_t #define DATA sdp_data_t #include "stdio.h" #include "string.h" #include "ctype.h" #include "unistd.h" #include "stdlib.h" #include "bluetooth/bluetooth.h" #include "bluetooth/sdp.h" #include "bluetooth/sdp_lib.h" #define DEV_ADDR "E4:12:1D:96:10:EF" // MAC address of service device main( int argc, char **argv) { // Server UUID: "d8308c4e-9469-4051-8adc-7a2663e415e2" static BYTE uuid[16] = { // UUID as byte array 0xd8, 0x30, 0x8c, 0x4e, 0x94, 0x69, 0x40, 0x51, 0x8a, 0xdc, 0x7a, 0x26, 0x63, 0xe4, 0x15, 0xe2 }; int chan; chan = GetServiceChannel( uuid ); if( chan > 0 ) { printf( "specified service is on channel %d\n", chan ); } else { fprintf( stderr, " can't find channel\n" ); } exit( 0 ); } int GetServiceChannel( BYTE *uuid) // uuid of service as 16 bytes { SESSION *s; UUID svc_uuid; LIST *response_list,*search_list,*attrid_list,*r; RECORD *rec; int range; int n; BYTE addr[6]; // define my own addr type int chan=0; // CONNECT TO SDP SERVER // (Note: device must be ON but server need not be running) str2ba( DEV_ADDR, (bdaddr_t *)&addr ); s = sdp_connect( BDADDR_ANY, (bdaddr_t *)&addr, SDP_RETRY_IF_BUSY ); if( !s ) { fprintf( stderr, "can't connect to sdp server\n" ); return( 0 ); } // CREATE QUERY LISTS sdp_uuid128_create( &svc_uuid, uuid ); search_list = sdp_list_append( NULL, &svc_uuid ); range = 0x0000ffff; // start at 0000, end at ffff attrid_list = sdp_list_append( NULL, &range ); // SEARCH FOR RECORDS // (Note: Server must be running) n = sdp_service_search_attr_req( s, search_list, SDP_ATTR_REQ_RANGE, attrid_list, &response_list ); if( n ) { fprintf( stderr, "search failed.\n" ); return( 0 );; } // CHECK IF ANY RESPONSES n = sdp_list_len( response_list ); if( n <= 0 ) { fprintf( stderr, "no responses.\n" ); return( 0 );; } // PROCESS RESPONSES r = response_list; while( r ) { // loop thru all responses sdp_record_t *rec; LIST *proto_list,*p; rec = (RECORD *)r->data; n = sdp_get_access_protos( rec, &proto_list ); if( n ) { fprintf( stderr, "can't get access protocols.\n" ); return( 0 ); } p = proto_list; while( p ) { // loop thru all protocols LIST *pds; int proto=0; pds = (LIST *)p->data; while( pds ) { // loop thru all pds DATA *d; int dtd; d = pds->data; // get data ptr of pds while( d ) { // loop over all data dtd = d->dtd; // get dtd of data switch( dtd ) { // which dtd? case SDP_UUID16: case SDP_UUID32: case SDP_UUID128: proto = sdp_uuid_to_proto( &d->val.uuid ); // get proto # break; case SDP_UINT8: if( proto == RFCOMM_UUID ) { // proto is rfcomm? chan = d->val.uint8; // save chan num } break; } d = d->next; // advance to next data unit } pds = pds->next; // advance to next pds } sdp_list_free( (LIST *)p->data, 0 ); p = p->next; // advance to next protocol } sdp_list_free( proto_list, 0 ); r = r->next; // advance to next response } return( chan ); // Return chan number [1-30] or 0 if not found }
To make:
gcc getchan.c -o getchan -l bluetooth
