Connect to an Android device with 'Wireless debugging' by scanning a QR code in .NET

AndroidWirelessDebuggingAutoConnect.cs

using System;
using System.Collections.Generic;
using System.Diagnostics;
using System.Net;
using System.Net.Sockets;
using System.Text;
using System.Threading;
using QRCoder;

/// <summary>
/// Disclaimer: Most of the mDNS related codebase is generated by ChatGPT.
/// </summary>
public class AndroidWirelessDebuggingAutoConnect
{
	private const string ADB_PATH = "adb.exe";

	/// <summary>
	/// If <c>true</c> and an Android device broadcasts a connection service, app will attempt to connect to that device without waiting for
	/// the pair service (which is broadcasted after the QR code is read). This is useful for quickly connecting to the last paired device
	/// without requiring the QR code to be read.
	/// </summary>
	private static bool canConnectWithoutPair = true;
	private static bool hasPaired;

	private class ServiceData
	{
		public readonly string Name;
		public readonly ushort Port;

		public ServiceData( string name, ushort port )
		{
			Name = name;
			Port = port;
		}
	}

	public static void Main( string[] args )
	{
		string name = GetRandomText( 5 );
		string password = GetRandomText( 6 );
		string pairServiceName = $"{name}_adb-tls-pairing";
		string connectServiceName = $"_adb-tls-connect._tcp.local";
		string qrCode = $"WIFI:T:ADB;S:{name};P:{password};;";

		Console.WriteLine( AsciiQRCodeHelper.GetQRCode( qrCode, QRCodeGenerator.ECCLevel.M, invert: false ) );

		using UdpClient client = new UdpClient();
		IPEndPoint localEp = new IPEndPoint( IPAddress.Any, 5353 );

		client.Client.SetSocketOption( SocketOptionLevel.Socket, SocketOptionName.ReuseAddress, true );
		client.ExclusiveAddressUse = false;
		client.Client.Bind( localEp );

		IPAddress multicastAddress = IPAddress.Parse( "224.0.0.251" );
		client.JoinMulticastGroup( multicastAddress );

		Console.WriteLine( "Scan the QR code with Wireless debugging..." );

		while( true )
		{
			try
			{
				if( hasPaired || canConnectWithoutPair )
					SendMdnsQuery( client, connectServiceName );

				byte[] data = client.Receive( ref localEp );
				List<ServiceData> discoveredServices = ParseMdnsPacket( data );

				if( !hasPaired && discoveredServices.Find( ( e ) => e.Name.Contains( pairServiceName ) ) is ServiceData pairService )
				{
					Console.WriteLine( $"Pairing with {localEp.Address}:{pairService.Port}..." );

					if( RunADBCommand( $"pair {localEp.Address}:{pairService.Port} {password}" ) )
					{
						hasPaired = true;
						client.Client.ReceiveTimeout = 5000;
						Console.WriteLine( "Fetching connection information..." );
					}
				}
				else if( ( hasPaired || canConnectWithoutPair ) && discoveredServices.Find( ( e ) => e.Name.Contains( connectServiceName ) ) is ServiceData connectService )
				{
					Console.WriteLine( $"Connecting to {localEp.Address}:{connectService.Port}..." );

					if( RunADBCommand( $"connect {localEp.Address}:{connectService.Port}" ) )
					{
						Console.WriteLine( "Connected to device! Press any key to exit..." );
						Console.ReadKey();

						return;
					}
					else if( canConnectWithoutPair )
					{
						Console.WriteLine( "Auto-connect failed. Scan the QR code to connect manually..." );
						canConnectWithoutPair = false;
					}
				}

				Thread.Sleep( 500 );
			}
			catch( TimeoutException )
			{
			}
		}
	}

	private static bool RunADBCommand( string command )
	{
		try
		{
			using( Process adb = new Process() )
			{
				adb.StartInfo = new ProcessStartInfo()
				{
					FileName = ADB_PATH,
					Arguments = command,
					UseShellExecute = false,
					CreateNoWindow = true,
					RedirectStandardOutput = true,
				};

				adb.Start();

				string output = adb.StandardOutput.ReadToEnd();
				Console.WriteLine( output );

				adb.WaitForExit();
				return adb.ExitCode == 0 && output.IndexOf( "failed", StringComparison.OrdinalIgnoreCase ) < 0;
			}
		}
		catch( Exception e )
		{
			Console.WriteLine( $"Error while running adb command: {e}" );
			return false;
		}
	}

	private static string GetRandomText( int length )
	{
		const string randomCharacters = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789";

		StringBuilder sb = new StringBuilder( length );
		for( int i = 0; i < length; i++ )
			sb.Append( randomCharacters[Random.Shared.Next( randomCharacters.Length )] );

		return sb.ToString();
	}

	private static void SendMdnsQuery( UdpClient udpClient, string serviceName )
	{
		byte[] query = ConstructMdnsQuery( serviceName );
		IPEndPoint endPoint = new IPEndPoint( IPAddress.Parse( "224.0.0.251" ), 5353 );
		udpClient.Send( query, query.Length, endPoint );
	}

	private static byte[] ConstructMdnsQuery( string serviceName )
	{
		// Header section
		byte[] header = new byte[12];
		header[5] = 1; // QDCOUNT (1 question)

		// Question section
		byte[] nameBytes = EncodeDomainName( serviceName );
		byte[] question = new byte[nameBytes.Length + 4];
		Buffer.BlockCopy( nameBytes, 0, question, 0, nameBytes.Length );
		question[nameBytes.Length] = 0; // QTYPE (A record)
		question[nameBytes.Length + 1] = 255; // PTR
		question[nameBytes.Length + 2] = 0; // QCLASS (IN)
		question[nameBytes.Length + 3] = 255;

		// Combine header and question sections
		byte[] query = new byte[header.Length + question.Length];
		Buffer.BlockCopy( header, 0, query, 0, header.Length );
		Buffer.BlockCopy( question, 0, query, header.Length, question.Length );

		return query;
	}

	private static byte[] EncodeDomainName( string domainName )
	{
		var parts = domainName.Split( '.' );
		var result = new byte[domainName.Length + 2]; // Include the length bytes and the final zero byte
		int index = 0;

		foreach( var part in parts )
		{
			result[index++] = (byte) part.Length;
			byte[] partBytes = Encoding.UTF8.GetBytes( part );
			Buffer.BlockCopy( partBytes, 0, result, index, partBytes.Length );
			index += partBytes.Length;
		}
		result[index] = 0; // Null terminator

		return result;
	}

	private static List<ServiceData> ParseMdnsPacket( byte[] data )
	{
		List<ServiceData> result = new List<ServiceData>( 1 );
		try
		{
			int index = 0;

			// Parse DNS header
			ushort transactionId = ReadUInt16( data, ref index );
			ushort flags = ReadUInt16( data, ref index );
			ushort questionCount = ReadUInt16( data, ref index );
			ushort answerCount = ReadUInt16( data, ref index );
			ushort authorityCount = ReadUInt16( data, ref index );
			ushort additionalCount = ReadUInt16( data, ref index );
			//Console.WriteLine( $"Transaction ID: {transactionId} Flags: {flags} Questions: {questionCount} Answers: {answerCount} Authority RRs: {authorityCount} Additional RRs: {additionalCount}" );

			// Parse DNS questions
			for( int i = 0; i < questionCount; i++ )
			{
				string questionName = ReadDomainName( data, ref index );
				ushort questionType = ReadUInt16( data, ref index );
				ushort questionClass = ReadUInt16( data, ref index );
				//Console.WriteLine( $"Question {i + 1} Name: {questionName} Type: {questionType} Class: {questionClass}" );
			}

			// Parse answers
			for( int i = 0; i < answerCount; i++ )
			{
				string answerName = ReadDomainName( data, ref index );
				ushort answerType = ReadUInt16( data, ref index );
				ushort answerClass = ReadUInt16( data, ref index );
				uint ttl = ReadUInt32( data, ref index );
				ushort dataLength = ReadUInt16( data, ref index );

				if( answerType == 33 ) // SRV record
				{
					ushort priority = ReadUInt16( data, ref index );
					ushort weight = ReadUInt16( data, ref index );
					ushort port = ReadUInt16( data, ref index );
					string target = ReadDomainName( data, ref index );
					//Console.WriteLine( $"Answer SRV: {answerName}, Port: {port}, Target: {target}, TTL: {ttl}" );

					result.Add( new ServiceData( answerName, port ) );
				}
				else
				{
					// Skip the rest of the data
					index += dataLength;
				}
			}

			for( int i = 0; i < authorityCount; i++ )
			{
				string name = ReadDomainName( data, ref index );
				ushort type = ReadUInt16( data, ref index );
				ushort classValue = ReadUInt16( data, ref index );
				uint ttl = ReadUInt32( data, ref index );
				ushort dataLength = ReadUInt16( data, ref index );

				if( type == 2 ) // NS record
				{
					string nsDomain = ReadDomainName( data, ref index );
					//Console.WriteLine( $"Authority NS: {name}, NS: {nsDomain}, TTL: {ttl}" );
				}
				else if( type == 6 ) // SOA record
				{
					string mName = ReadDomainName( data, ref index );
					string rName = ReadDomainName( data, ref index );
					uint serial = ReadUInt32( data, ref index );
					uint refresh = ReadUInt32( data, ref index );
					uint retry = ReadUInt32( data, ref index );
					uint expire = ReadUInt32( data, ref index );
					uint minimum = ReadUInt32( data, ref index );
					//Console.WriteLine( $"Authority SOA: {name}, MNAME: {mName}, RNAME: {rName}, Serial: {serial}, Refresh: {refresh}, Retry: {retry}, Expire: {expire}, Minimum: {minimum}" );
				}
				else if( type == 33 ) // SRV record
				{
					ushort priority = ReadUInt16( data, ref index );
					ushort weight = ReadUInt16( data, ref index );
					ushort port = ReadUInt16( data, ref index );
					string target = ReadDomainName( data, ref index );
					//Console.WriteLine( $"Authority SRV: {name}, Port: {port}, Target: {target}, TTL: {ttl}" );

					result.Add( new ServiceData( name, port ) );
				}
				else
				{
					// Skip the rest of the data
					index += dataLength;
				}
			}

			for( int i = 0; i < additionalCount; i++ )
			{
				string name = ReadDomainName( data, ref index );
				ushort type = ReadUInt16( data, ref index );
				ushort classValue = ReadUInt16( data, ref index );
				uint ttl = ReadUInt32( data, ref index );
				ushort dataLength = ReadUInt16( data, ref index );

				if( type == 33 ) // SRV record
				{
					ushort priority = ReadUInt16( data, ref index );
					ushort weight = ReadUInt16( data, ref index );
					ushort port = ReadUInt16( data, ref index );
					string target = ReadDomainName( data, ref index );
					//Console.WriteLine( $"Additional SRV: {name}, Port: {port}, Target: {target}, TTL: {ttl}" );

					result.Add( new ServiceData( name, port ) );
				}
				else
				{
					// Skip the rest of the data
					index += dataLength;
				}
			}
		}
		catch( Exception ex )
		{
			Console.WriteLine( $"Error parsing mDNS packet: {ex}" );
		}

		return result;
	}

	private static string ReadDomainName( byte[] data, ref int index )
	{
		StringBuilder name = new StringBuilder();
		while( data[index] != 0 )
		{
			byte length = data[index++];
			if( ( length & 0xC0 ) == 0xC0 ) // Compression
			{
				ushort pointer = (ushort) ( ( ( length & 0x3F ) << 8 ) | data[index++] );
				int savedIndex = index;
				index = pointer;
				name.Append( ReadDomainName( data, ref index ) );
				index = savedIndex;
				return name.ToString();
			}

			if( name.Length > 0 )
				name.Append( '.' );

			name.Append( Encoding.UTF8.GetString( data, index, length ) );
			index += length;
		}

		index++; // Skip the null byte at the end of the domain name
		return name.ToString();
	}

	private static ushort ReadUInt16( byte[] data, ref int index )
	{
		ushort value = (ushort) ( ( data[index] << 8 ) | data[index + 1] );
		index += 2;
		return value;
	}

	private static uint ReadUInt32( byte[] data, ref int index )
	{
		uint value = (uint) ( ( data[index] << 24 ) | ( data[index + 1] << 16 ) | ( data[index + 2] << 8 ) | data[index + 3] );
		index += 4;
		return value;
	}
}

How To

• Create a new .NET console application with the attached code
• Add QRCoder NuGet package
• If adb.exe isn't added to PATH, either add it to PATH or change the value of ADB_PATH constant
• Run the console application
• Enable Wireless debugging on Android device and scan the QR code
• Wait a few seconds for the pairing and connection steps to complete
• Since the Android device remembers the paired workstations, in the future it's sufficient to run the console application and enable Wireless debugging. The console will attempt to connect to the Android device automatically without scanning the QR code

Disclaimer: I've used ChatGPT to handle mDNS query and discovery stuff. It's amazing how ChatGPT could provide working code samples while I couldn't find a single documentation or example code online about these mDNS stuff.

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Scan the QR code with Wireless debugging...
Pairing with 192.168.0.55:38809...
Successfully paired to 192.168.0.55:38809 [guid=adb-1AA2F002802-r11Tsn]

Fetching connection information...
Connecting to 192.168.0.55:41401...
connected to 192.168.0.55:41401

Connected to device! Press any key to exit...