Using Bluetooth Classic on Linux

[peterfoot]

There isn't a separate platform identifier for Linux for NuGet packages so currently the generic .NET6.0 and .NET7.0 assemblies contain only the Linux implementation. For Windows you need to ensure your consuming project targets a Windows specific platform. The Linux implementation is not yet complete so there are some limitations with using it. The main one being a lack of support so far for SDP querying so in order to connect a BluetoothClient you need to know the numerical port (channel) to connect to the service of choice. For some devices this is hard-coded as port 1 for a single Serial Port peripheral but you cannot assume this without investigating the target device. The following snippet shows how to connect with a specific port (the UUID is currently ignored but will eventually be implemented):-

client.Connect(new BluetoothEndPoint(device.DeviceAddress, BluetoothService.SerialPort, 1));
if (client.Connected)
{
    Debug.WriteLine("Connected");
    var stream = client.GetStream();
    StreamWriter writer = new StreamWriter(stream);
    writer.WriteLine("32feet.NET\r\n==========\r\n\r\nHello from Linux!\r\nGreat to be here!\r\n");
    writer.Flush();
    writer.Close();
    client.Close();
}

[embeddedmz]

@peterfoot I have NET 6 installed on Ubuntu but I got this exception :

amine@Lenovo-Y50-70:~/DevProjects/CSharpBT/bin/Debug/net6.0$ dotnet QuickBTTest.dll
Unhandled exception. System.NotImplementedException: This functionality is not implemented in the portable version of this assembly. You should reference the NuGet package from your main application project in order to reference the platform-specific implementation.
   at InTheHand.Net.Sockets.BluetoothClient.PlatformInitialize()
   at InTheHand.Net.Sockets.BluetoothClient..ctor()
   at QuickBTTest.Program.Main(String[] args) in /home/amine/DevProjects/CSharpBT/Program.cs:line 35
Abandon (core dumped)

[peterfoot]

That error suggests that your project has built in the .NET Standard dll. What .NET version does your project target?

[embeddedmz]

I made a small program to test InTheHand.Net. (4.0.36) and I build it using the command dotnet build on the Ubuntu machine.

amine@Lenovo-Y50-70:~$ dotnet --version
6.0.413

I didn't understand your answer

Actually I'm trying to use the bluetooth port via the class SerialPort and /usr/bin/rfcomm bind but I'm not receiving the reply of my bluetooth device :\

[peterfoot]

It's the project file which determines what dependencies are used, rather than the runtime version on your machine e.g.

<Project Sdk="Microsoft.NET.Sdk">

  <PropertyGroup>
    <OutputType>Exe</OutputType>
    <TargetFramework>net7.0</TargetFramework>
    <ImplicitUsings>enable</ImplicitUsings>
    <Nullable>enable</Nullable>
	  <DebugSymbols>true</DebugSymbols>
	  <DebugType>portable</DebugType>
  </PropertyGroup>

This pulls in the .net7.0 version of the dll in the NuGet package. The targetframework needs to be net.60 or net7.0 for the library to work on linux.

[embeddedmz]

I'm using NET 6 :

  <PropertyGroup>
    <OutputType>Exe</OutputType>
    <TargetFramework>net6.0</TargetFramework>
    <ImplicitUsings>enable</ImplicitUsings>
    <Nullable>enable</Nullable>
  </PropertyGroup>

  <ItemGroup>
    <PackageReference Include="InTheHand.Net.Bluetooth" Version="4.0.36" />
    <PackageReference Include="System.IO.Ports" Version="6.0.0" />
  </ItemGroup>

Otherwise, I found a solution to use the bluetooth port, however I must launch the program with sudo since SerialPort is unable to open /dev/rfcommm : this is very annoying and I must fix this problem before using the code in a real project.

Below the quick and dirty code I wrote to test the workaround :

/*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);
            }
        }
    }
}