L2CAP IOS + Linux (Bluez) - ios

Question

I'm trying to make a simple L2CAP Socket communication between IOS and a Linux PC.
I've been able to:
Create an L2CAP connection between two Linux machines (using example code from https://github.com/atwilc3000/sample/tree/master/Bluetooth)
Create an L2CAP connection between two Iphones (using example code from https://github.com/github-deden/iOS_L2Cap)
On that IOS example they are using some PSM advertise in order to chose the correct PSM for the L2CAP channel. On the integration, I've set a fixed PSM on both sides. The Iphone is connecting to the Linux machine fixed PSM. I've tried multiple PSM (0x1001, 0x25).
The problem is, I can't connect and can't get any information on what is happening on the air.
My question is, do I need to implement a dynamic/advertise PSM on the Linux application? Do I need to pick a specific PSM? Have you been able to make this work? Do you have any suggestions?
Thanks in advance!
Server code:
#include <stdio.h>
#include <unistd.h>
#include <string.h>
#include <stdlib.h>
#include <sys/socket.h>
#include <bluetooth/bluetooth.h>
#include <bluetooth/l2cap.h>
#include "l2cap_socket.h"
int main(int argc, char **argv)
{
struct sockaddr_l2 loc_addr = { 0 }, rem_addr = { 0 };
char buf[1024] = { 0 };
int server_socket, client_socket, bytes_read;
unsigned int opt = sizeof(rem_addr);
printf("Start Bluetooth L2CAP server...\n");
/* allocate socket */
server_socket = socket(AF_BLUETOOTH, SOCK_SEQPACKET, BTPROTO_L2CAP);
/* bind socket to the local bluetooth adapter */
loc_addr.l2_family = AF_BLUETOOTH; /* Addressing family, always AF_BLUETOOTH */
bacpy(&loc_addr.l2_bdaddr, BDADDR_ANY); /* Bluetooth address of local bluetooth adapter */
loc_addr.l2_psm = htobs(L2CAP_SERVER_PORT_NUM); /* port number of local bluetooth adapter */
printf("binding\n");
if(bind(server_socket, (struct sockaddr *)&loc_addr, sizeof(loc_addr)) < 0) {
perror("failed to bind");
exit(1);
}
printf("listening\n");
/* put socket into listening mode */
listen(server_socket, 1);
/* accept one connection */
client_socket = accept(server_socket, (struct sockaddr *)&rem_addr, &opt); /* return new socket for connection with a client */
ba2str( &rem_addr.l2_bdaddr, buf );
printf("connected from %s\n", buf);
/* read data from the client */
memset(buf, 0, sizeof(buf));
bytes_read = recv(client_socket, buf, sizeof(buf), 0);
if( bytes_read > 0 ) {
printf("received [%s]\n", buf);
}
/* close connection */
close(client_socket);
close(server_socket);
return 0;
}
Client is based on (from https://github.com/bluekitchen/CBL2CAPChannel-Demo).

Answer 1

I have now a working version based on https://github.com/bluekitchen/btstack
On the iOS side i have been using https://github.com/bluekitchen/CBL2CAPChannel-Demo
On the server side le_data_channel_server.