Bluetooth RFComm on a C# program running on Linux

Question

I haven't found a NuGet package that allows me to do Bluetooth RFComm in a C# program running under Linux.

In addition, I would like to provide a Stream object to the API that will use the bluetooth port.

Linux.Bluetooth (uses Tmds.DBus to access D-Bus) supports only BLE and InTheHand.Net doesn't have GNU/Linux support.

Can anyone suggest a simple strategy for implementing this feature ? To access the D-Bus, I can use Tmds.DBus, but how do I create the Stream object ?

Update : I think it's better to use a C++/Qt (or a Python) program to handle this part and use a TCP socket to communicate between the C# program and the other having access to

Update 2 : I found this article and I don't know if I can create the same type of sockets on a C# program : https://people.csail.mit.edu/albert/bluez-intro/c404.html => No, when compiling the client program, I needed to install this Ubuntu packet : libbluetooth-dev and to link the program to libbluetooth. I can try importing C libraries into the C# program...

Answer 1

A simple solution is to use a virtual serial device to communicate with a Bluetooth device.

I'm sharing with you a quick and dirty example of how to use the bluetooth port in a C# program running under Ubuntu.

The program must be launched with the sudo command since SerialPort is unable to open /dev/rfcomm1 (the virtual serial port created with the command rfcomm bind) without root privileges but I think there's an easy workaround to fix that.

//using InTheHand.Net;
//using InTheHand.Net.Bluetooth;
//using InTheHand.Net.Sockets;
using System;
using System.Diagnostics;
using System.IO.Ports;
using System.Net.Mail;
using System.Text;

namespace QuickBTTest
{
    internal class Program
    {
        static void Main(string[] args)
        {
            byte[] outBuffer = new byte[12];
            byte[] inBuffer = new byte[6];

            outBuffer[0] = (byte)'$';
            outBuffer[1] = (byte)'P';
            outBuffer[2] = (byte)'R';
            outBuffer[3] = 12;
            outBuffer[4] = 0;
            outBuffer[5] = 100;
            outBuffer[6] = 0;
            outBuffer[7] = 50;
            outBuffer[8] = 0;
            outBuffer[9] = 200;
            ushort cs = 0;
            for (int i = 1; i < 10; i++)
            {
                cs = (ushort)(cs + outBuffer[i]);
            }
            outBuffer[10] = (byte)(cs >> 8);
            outBuffer[11] = (byte)cs;

            string address = "88:6B:0F:84:64:1C";

            string devicePath = "/dev/rfcomm0";
            int port = 1;

            if (!File.Exists(devicePath))
            {
                try
                {
                    Process rfcommProcess = new Process();
                    rfcommProcess.StartInfo.FileName = "sudo";
                    rfcommProcess.StartInfo.Arguments = $"/usr/bin/rfcomm bind {devicePath} {address} {port}";
                    rfcommProcess.StartInfo.UseShellExecute = false;
                    rfcommProcess.StartInfo.RedirectStandardOutput = true;
                    rfcommProcess.StartInfo.RedirectStandardError = true;
                    rfcommProcess.Start();

                    /*string error = rfcommProcess.StandardError.ReadToEnd();

                    if (!string.IsNullOrWhiteSpace(error))
                    {
                        Console.WriteLine($"Bluetooth bind error : {error}");
                        return;
                    }*/

                    rfcommProcess.WaitForExit(3000);
                }
                catch (Exception e)
                {
                    Console.WriteLine($"Bluetooth bind error : {e.Message}");
                    return;
                }
            }

            if (File.Exists(devicePath))
            {
                SerialPort serialPort = new SerialPort();
                serialPort.PortName = devicePath;
                serialPort.BaudRate = 115200;
                serialPort.ReadTimeout = 5000;

                serialPort.Open();

                if (serialPort.IsOpen)
                {
                    serialPort.Write(outBuffer, 0, outBuffer.Length);

                    Console.WriteLine("Wait for response... press enter");
                    Console.ReadLine();

                    int ret = serialPort.Read(inBuffer, 0, inBuffer.Length);
                    if (ret > 0)
                    {
                        Console.WriteLine("Rcvd response :");
                        for (int i = 0; i < ret; i++)
                        {
                            Console.Write(inBuffer[i] + ", ");
                        }
                        Console.WriteLine();
                    }
                }

                serialPort.Close();

                Process tCmd = new Process();
                tCmd.StartInfo.FileName = "sudo";
                tCmd.StartInfo.Arguments = $"/usr/bin/rfcomm release {devicePath}";
                tCmd.StartInfo.UseShellExecute = false;
                tCmd.StartInfo.RedirectStandardOutput = true;
                tCmd.StartInfo.RedirectStandardError = true;
                tCmd.Start();

                string output = tCmd.StandardOutput.ReadToEnd();
                string err = tCmd.StandardError.ReadToEnd();

                tCmd.WaitForExit(5000);
            }
        }
    }
}