How to establish a continuous Bluetooth connection with BlueZ so I can transfer to and receive data-CodePudding

I've been making a map making robot car with Arduino for class. I want to make a user interface for it in C (on a PC running Linux) that would work like this: the user can press a Start and a Stop button, or click a specific area of the map to send the robot to there. Right now my test setup code looks like this: Arduino: `

if (BTSerial.available() > 0) {
    c = BTSerial.readStringUntil('\n').toInt();
    BTSerial.write(c);
    if(c == 8) {
      Buzzing(SOS);
      BTSerial.println("eight");
    }
  }

**PC program**:

#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] = "98:DA:60:03:F2:92";

    // 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, "8", 2);
    }

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

    int client, bytes_read;
    char buf[1024] = { 0 };
    // put socket into listening mode
    listen(s, 1);

    // read data from the client
    bytes_read = read(client, buf, sizeof(buf));
    if( bytes_read > 0 ) {
        printf("received [%s]\n", buf);
    }

    close(s);
    return 0;
}

` Ideally if I send the number 8 to the Arduino it would send back the string "eight". When I run my PC program, my PC connects to the Arduino (I get a notification from the OS that my PC is connected and also the led on my HC-06 Bluetooth module connected to the Arduino stops blinking signaling that a device was connected to it) and the buzzer connected to the Arduino starts buzzing the morse code of SOS as expected. However after a second my program terminates, the Bluetooth connection ends (I get a notification that my PC is disconnected and the led on the Bluetooth module starts blinking again) and I don't get back the expected "eight" string. I'm still just a beginner when it comes to the C language and since I can not find a detailed documentation of BlueZ, I'm kind of stuck. Any help would be greatly appreciated!

I tried to combine the server and the client code from this site: https://people.csail.mit.edu/albert/bluez-intro/x502.html#rfcomm-server.c

I also tested my code on the Arduino using Putty on PC and it worked with it properly.

CodePudding user response：

Calling listen on the socket doesn't do what you think it does. Listening does not mean "wait for data". It means "wait for connect". And you cannot read from the listening socket; you can only accept the connection.

Your socket is already connected. Don't listen. Just read.

CodePudding user response：

So after a bit of work I finally could get it working. I only needed to change the first parameter of the read() function. Here's my final code:

#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 }, rem_addr = { 0 };
    int s, status;
    char dest[18] = "98:DA:60:03:F2:92";

    // 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, "8", 2);
    }

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

    int bytes_read;
    char buf[1024] = { 0 };

    // read data from the client
    bytes_read = read(s, buf, sizeof(buf));
    if( bytes_read > 0 ) {
        printf("%s", buf);
    }

    close(s);
    return 0;
}

This code sends the number "8" to the Arduino, to which the Arduino replies with the string "eight". It's probably not the nicest C code for Bluetooth connection, but at least it's working I guess.