How can I send more bytes using Bluez L2CAP?

Question

I have the following code that connects to another machine using BlueZ and sends packets:

struct sockaddr_l2 addr = { 0 };
    int s, status;
    char dest[18] = "DC:FB:48:6B:BF:0B";

    int socket1;

    int32_t value = 0;

    // allocate a socket
    socket1 = socket(AF_BLUETOOTH, SOCK_SEQPACKET, BTPROTO_L2CAP);


    // set the connection parameters (who to connect to)
    addr.l2_family = AF_BLUETOOTH;
    addr.l2_psm = htobs(0x1001);

    str2ba( dest, &addr.l2_bdaddr );
    status = connect(socket1, (struct sockaddr *)&addr, sizeof(addr));
    while( status != 0)
    {
        status = connect(socket1, (struct sockaddr *)&addr, sizeof(addr));
        std::cout << "Waiting for DC:FB:48:6B:BF:0B" << std::endl;
        sleep(2);
    }

    while (true)
    {
        double data[512] = {0.0};
        memset(data, 0, 512);
        status = write(socket1, data, 512);
     }

As you can see, I just send 512 bytes and other machine reads them just fine. However, when I try to increase to 1000 bytes, other machine can no longer accept any bytes and just does nothing.

How can I send more bytes in this case? I am using Linux CentOS 8.

Answer 1

By default the maximum transmission rate of L2CAP is 672 bytes. I would recommend you to try setting the maximum transmission unit to your required value.

Have a look at "4.3.1 Maximum Transmission Unit" here.