Availability Anywhere Part 15 — TCP over Serial Port

This is the fifteenth part of the Availability Anywhere series. For your convenience you can find other parts in the table of contents in Part 1 – Connecting to SSH tunnel automatically in Windows

You can’t forward a named pipe between the host and the guest VM, but we can forward the named pipe as a serial port to the VM. So the host writes to the named pipe, and the VM reads from the serial port. Let’s see the server now:

using System;
using System.IO.Ports;
using System.Linq;
using System.Net;
using System.Net.Sockets;
using System.Threading;
using System.IO;

namespace PipeProxy
{
    class PortServer
    {
        public static void Start(string[] args)
        {
            var destinationIp = args[1].Split(':')[0];
            var destinationPort = int.Parse(args[1].Split(':')[1]);
            var portName = args[2];

            Console.WriteLine($"Routing to {destinationIp}:{destinationPort} via {portName}");

            Console.WriteLine("Connecting");
            //In theory I can set baud rate to 268435456
            //In practice the max is 115200
            SerialPort port = new SerialPort(portName, 115200, Parity.None, 8, StopBits.One)
            {
                ReadBufferSize = 10000000,
                WriteBufferSize = 10000000
            };

            while (true)
            {
                try
                {
                    while (true)
                    {
                        Thread.Sleep(1000);
                        if (port.IsOpen)
                        {
                            continue;
                        }
                        else
                        {
                            port.Open();
                            Console.WriteLine("Connected");
                        }

                        // I'm forcing IPv4 (IPv6 breaks with Cisco AnyConnect)
                        IPEndPoint remoteEP = new IPEndPoint(Dns.GetHostEntry(destinationIp).AddressList.First(a => a.AddressFamily == AddressFamily.InterNetwork), destinationPort);
                        Socket senderSocket = new Socket(remoteEP.AddressFamily, SocketType.Stream, ProtocolType.Tcp);

                        senderSocket.Connect(remoteEP);
                        Console.WriteLine("Socket connected to {0}", senderSocket.RemoteEndPoint);

                        new Thread(() =>
                        {
                            var socket = new PortSocket(senderSocket, port, r => { }, s => { });
                            socket.Start();
                        }).Start();
                    }
                }
                catch (Exception e)
                {
                    Console.WriteLine("Exception " + e);
                }
            }
        }
    }
	
    public class PortSocket
    {
        private Socket clientSocket;
        private SerialPort port;
        private Action<int> received;
        private Action<int> sent;
        public PortSocket(Socket socket, SerialPort port, Action<int> received, Action<int> sent)
        {
            this.clientSocket = socket;
            this.port = port;
            this.received = received;
            this.sent = sent;
        }

        public void Start()
        {
            Thread clientThread = new Thread(() =>
            {
                try
                {
                    var buffer = new byte[100000];
                    while (true)
                    {
                        var read = clientSocket.Receive(buffer);

                        if (read == 0)
                        {
                            port.Close();
                            return;
                        }

                        while (true)
                        {
                            try
                            {
                                port.Write(buffer, 0, read);
                                sent(read);
                                break;
                            }
                            catch (Exception e2)
                            {
                                Console.WriteLine("Exception when writing to pipe" + e2);
                            }
                        }
                    }
                }
                catch (Exception e)
                {
                    Console.WriteLine("Exception in client thread: " + e);
                }
            });

            try
            {
                Thread senderThread = new Thread(KeepReading);
                senderThread.Start();
            }
            catch (Exception e)
            {
                Console.WriteLine("Exception  " + e);
            }

            clientThread.Start();
            clientThread.Join();
        }

        private void KeepReading()
        {
            int totalRead = 0;
            int toRead = 100024;

            byte[] bytes = new byte[toRead];
            try
            {
                while (true)
                {
                    int howMuchRead = port.Read(bytes, 0, toRead);

                    if (howMuchRead == 0)
                        break;

                    totalRead += howMuchRead;
                    received(howMuchRead);
                    clientSocket.Send(bytes, 0, howMuchRead, SocketFlags.None);
                }
            }
            catch (Exception e)
            {
                Console.WriteLine("Exception while reading" + e);
            }
        }
    }
}

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using System;

using System.IO.Ports;

using System.Linq;

using System.Net;

using System.Net.Sockets;

using System.Threading;

using System.IO;

namespace PipeProxy

{

class PortServer

{

public static void Start(string[] args)

{

var destinationIp = args[1].Split(':')[0];

var destinationPort = int.Parse(args[1].Split(':')[1]);

var portName = args[2];

Console.WriteLine($"Routing to {destinationIp}:{destinationPort} via {portName}");

Console.WriteLine("Connecting");

//In theory I can set baud rate to 268435456

//In practice the max is 115200

SerialPort port = new SerialPort(portName, 115200, Parity.None, 8, StopBits.One)

{

ReadBufferSize = 10000000,

WriteBufferSize = 10000000

};

while (true)

{

try

{

while (true)

{

Thread.Sleep(1000);

if (port.IsOpen)

{

continue;

}

else

{

port.Open();

Console.WriteLine("Connected");

}

// I'm forcing IPv4 (IPv6 breaks with Cisco AnyConnect)

IPEndPoint remoteEP = new IPEndPoint(Dns.GetHostEntry(destinationIp).AddressList.First(a => a.AddressFamily == AddressFamily.InterNetwork), destinationPort);

Socket senderSocket = new Socket(remoteEP.AddressFamily, SocketType.Stream, ProtocolType.Tcp);

senderSocket.Connect(remoteEP);

Console.WriteLine("Socket connected to {0}", senderSocket.RemoteEndPoint);

new Thread(() =>

{

var socket = new PortSocket(senderSocket, port, r => { }, s => { });

socket.Start();

}).Start();

}

catch (Exception e)

{

Console.WriteLine("Exception " + e);

}

public class PortSocket

{

private Socket clientSocket;

private SerialPort port;

private Action<int> received;

private Action<int> sent;

public PortSocket(Socket socket, SerialPort port, Action<int> received, Action<int> sent)

{

this.clientSocket = socket;

this.port = port;

this.received = received;

this.sent = sent;

}

public void Start()

{

Thread clientThread = new Thread(() =>

{

try

{

var buffer = new byte[100000];

while (true)

{

var read = clientSocket.Receive(buffer);

if (read == 0)

{

port.Close();

return;

}

while (true)

{

try

{

port.Write(buffer, 0, read);

sent(read);

break;

}

catch (Exception e2)

{

Console.WriteLine("Exception when writing to pipe" + e2);

}

catch (Exception e)

{

Console.WriteLine("Exception in client thread: " + e);

}

});

try

{

Thread senderThread = new Thread(KeepReading);

senderThread.Start();

}

catch (Exception e)

{

Console.WriteLine("Exception " + e);

}

clientThread.Start();

clientThread.Join();

}

private void KeepReading()

{

int totalRead = 0;

int toRead = 100024;

byte[] bytes = new byte[toRead];

try

{

while (true)

{

int howMuchRead = port.Read(bytes, 0, toRead);

if (howMuchRead == 0)

break;

totalRead += howMuchRead;

received(howMuchRead);

clientSocket.Send(bytes, 0, howMuchRead, SocketFlags.None);

}

catch (Exception e)

{

Console.WriteLine("Exception while reading" + e);

}

And here is the benchmark:

Pipe -> Serial (115200 baud rate)
Mode: PipeProxyVirtualMachine
1       0.993
10      2.364
100     2.452
1000    9.119
10000   85.12
100000  844.847

Pipe -> Serial (115200 baud rate)

Mode: PipeProxyVirtualMachine

1 0.993

10 2.364

100 2.452

1000 9.119

10000 85.12

100000 844.847

It works, but slows down linearly with the size. Why? That’s because the serial port has a max bandwidth (that we call baud rate). Here it is 115200 (around 112 kBps). While this works much faster for small packets, this won’t give a decent performance for RDP with bigger bandwidth requirements.

Can we do better? One solution would be to emulate a COM port that has a bigger bandwidth. However, I don’t know a solution yet.