HTTPS proxy implementation, how to detect a completed request

Question

I'm attempting to write a simple async https proxy server in c#.

I would like to know how I should detect/handle when the request is complete, and how to exit my bActive loop, assuming a loop like this is appropriate.

Would really appreciate some pointers on if my approach is correct and what I could do to improve the logic.

The issue I seem to be running into is that the time it takes for an endpoint to respond along with the network delay means I DataAvailable doenst always have data but there may still be some sending. Requiring a sleep and another attmempt which in turn causes the long completion time in requests.

1. Listen for TCP connection

2. Extract CONNECT header and open a connection to the requested server

3. Copy the requestStream to proxyStream

4. Copy the proxyStream to the requestStream

5. Sleep waiting for data and repeat 3 - 4 until no data is avaiable on both streams. Then break out of the loop and close connection.

public async Task Start()
{
    listener.Start();

    while (listen)
    {
        if (listener.Pending())
        {
            HandleClient(await listener.AcceptTcpClientAsync());
        }
        else
        {
            await Task.Delay(100); //<--- timeout
        }
    }
}

private static async Task HandleClient(TcpClient clt)
{

    var bytes = new byte[clt.ReceiveBufferSize];
    var hostHeaderAvailable = 0;
    NetworkStream requestStream = null;
    int count;
    const string connectText = "connect";
    const string hostText = "Host: ";
    bool bActive = true;
    List<Task> tasks = new List<Task>();


    try
    {
        using (NetworkStream proxyStream = clt.GetStream())
        using (TcpClient requestClient = new TcpClient())
        {
            proxyStream.ReadTimeout = 100;
            proxyStream.WriteTimeout = 100;


            while (bActive)
            {
            
                if (proxyStream.DataAvailable && hostHeaderAvailable == 0)
                {
                    count = await proxyStream.ReadAsync(bytes, 0, bytes.Length);

                    var text = Encoding.UTF8.GetString(bytes);
                    Console.WriteLine(text);

                    if (text.ToLower().StartsWith(connectText))
                    {
                        // extract the url and port
                        var host = text.Remove(0, connectText.Length + 1);
                        var hostIndex = host.IndexOf(" ", StringComparison.Ordinal);
                        var hostEntry = host.Remove(hostIndex).Split(new[] { ":" }, StringSplitOptions.None);
                        // connect to the url and prot supplied
                        await requestClient.ConnectAsync(hostEntry[0], Convert.ToInt32(hostEntry[1]));
                        requestStream = requestClient.GetStream();

                        requestStream.ReadTimeout = 100;
                        requestStream.WriteTimeout = 100;

                        // send 200 response to proxyStream 
                        const string sslResponse = "HTTP/1.0 200 Connection established\r\n\r\n";
                        var sslResponseBytes = Encoding.UTF8.GetBytes(sslResponse);
                        await proxyStream.WriteAsync(sslResponseBytes, 0, sslResponseBytes.Length);

                        // delay here seems to prevent the following proxyStream.read from failing as data is not yet avaiable
                        // without it the loop runs and has to timeout before running again
                        await Task.Delay(1);
                    }
                }
                hostHeaderAvailable++;


                if (requestStream == null || !requestClient.Connected || !clt.Connected)
                {
                    bActive = false;
                    break;
                }

                Console.WriteLine(proxyStream.DataAvailable || requestStream.DataAvailable);

                if (proxyStream.DataAvailable || requestStream.DataAvailable)
                { 
                    Task task = proxyStream.CopyToAsync(requestStream);
                    Task task2 = requestStream.CopyToAsync(proxyStream);

                    tasks.Add(task);
                    tasks.Add(task2);

                    await Task.WhenAll(tasks).ConfigureAwait(false);
                    bActive = false;
                    break;
                }

                await Task.Delay(10);
            }
        }
    }
    catch (Exception e)
    {
        Console.WriteLine(e.ToString());
    }

    clt.Close();
}

An older attempt that used ReadAsync/WriteAsync too longer to response and still had the timeout issue.

1. Listen for TCP connection

2. Extract CONNECT header and open a connection to the requested server

3. Read data from requestStream and copy to proxyStream

4. Wait checking if data is avaiable on either stream

5. If data avaiable read from proxyStream and write to requestStream

6. If data avaiable read from requestStream and write to proxyStream

7. Sleep waiting for data and repeat 5 - 6 until no data is avaiable on eitboth streams. Then break out of the loop and close connection.

private static TcpListener listener = new TcpListener(IPAddress.Parse("192.168.0.25"), 13000);
private static bool listen = true;


public async Task Start()
{
    listener.Start();

    while (listen)
    {
        if (listener.Pending())
        {
            await HandleClient(await listener.AcceptTcpClientAsync());
        }
        else
        {
            await Task.Delay(100); 
        }
    }
}


private static async Task HandleClient(TcpClient clt)
{

    var bytes = new byte[clt.ReceiveBufferSize];
    var hostHeaderAvailable = 0;
    NetworkStream requestStream = null;
    int count;
    const string connectText = "connect";
    const string hostText = "Host: ";

    bool bActive = true;

    try
    {
        using (NetworkStream proxyStream = clt.GetStream())
        using (TcpClient requestClient = new TcpClient())
        {
            while (bActive)
            {
                while (proxyStream.DataAvailable)
                {
                    // handle connect
                    if (hostHeaderAvailable == 0)
                    {
                        count = await proxyStream.ReadAsync(bytes, 0, bytes.Length);

                        var text = Encoding.UTF8.GetString(bytes);
                        Console.WriteLine(text);

                        if (text.ToLower().StartsWith(connectText))
                        {
                            // extract the url and port
                            var host = text.Remove(0, connectText.Length + 1);
                            var hostIndex = host.IndexOf(" ", StringComparison.Ordinal);
                            var hostEntry = host.Remove(hostIndex).Split(new[] { ":" }, StringSplitOptions.None);
                            // connect to the url and prot supplied
                            await requestClient.ConnectAsync(hostEntry[0], Convert.ToInt32(hostEntry[1]));
                            requestStream = requestClient.GetStream();
                            // send 200 response to proxyStream 
                            const string sslResponse = "HTTP/1.0 200 Connection established\r\n\r\n";
                            var sslResponseBytes = Encoding.UTF8.GetBytes(sslResponse);
                            await proxyStream.WriteAsync(sslResponseBytes, 0, sslResponseBytes.Length);

                            // delay here seems to prevent the following proxyStream.read from failing as data is not yet avaiable
                            // without it the loop runs and has to timeout before running again
                            await Task.Delay(20);
                        }
                    }
                    hostHeaderAvailable++;

                    if (requestClient.Connected && hostHeaderAvailable > 1)
                    {
                        count = await proxyStream.ReadAsync(bytes, 0, bytes.Length);
                        await requestStream.WriteAsync(bytes, 0, count);
                    }
                }

                while (requestStream.DataAvailable)
                {
                    count = await requestStream.ReadAsync(bytes, 0, bytes.Length);
                    await proxyStream.WriteAsync(bytes, 0, count);
                }


                // attempt to detect a timeout / end of data avaiable
                var timeout = 0;
                while (!proxyStream.DataAvailable && !requestStream.DataAvailable)
                {
                    if (timeout > 5)
                    {
                        bActive = false;
                        break;
                    }

                    await Task.Delay(10);
                    timeout++;
                }
            }

        }

    }
    catch (Exception e)
    {
        Console.WriteLine(e.ToString());
    }
}

UPDATE

As per AgentFire's answer I have now come to the following working code:

public static async Task HandleDisconnect(TcpClient tcp, TcpClient tcp2, CancellationToken cancellationToken)
{
    while (true)
    {
        if (tcp.Client.Poll(0, SelectMode.SelectRead))
        {
            byte[] buff = new byte[1];

            if (tcp.Client.Receive(buff, SocketFlags.Peek) == 0)
            {
                // Client disconnected
                Console.WriteLine("The requesting client has dropped its connection.");
                cancellationToken = new CancellationToken(true);
                break;
            }
        }
        if (tcp2.Client.Poll(0, SelectMode.SelectRead))
        {
            byte[] buff = new byte[1];

            if (tcp2.Client.Receive(buff, SocketFlags.Peek) == 0)
            {
                // Server disconnected
                Console.WriteLine("The destination client has dropped its connection.");
                cancellationToken = new CancellationToken(true);
                break;
            }
        }

        await Task.Delay(1);
    }
}


private static async Task HandleClient(TcpClient clt)
{
    List<Task> tasks            = new List<Task>();
    var bytes                   = new byte[clt.ReceiveBufferSize];
    var hostHeaderAvailable     = 0;
    NetworkStream requestStream = null;
    const string connectText    = "connect";

    try
    {
        using (NetworkStream proxyStream = clt.GetStream())
        using (TcpClient requestClient = new TcpClient())
        {
            proxyStream.ReadTimeout = 100;
            proxyStream.WriteTimeout = 100;

            if (proxyStream.DataAvailable && hostHeaderAvailable == 0)
            {
                await proxyStream.ReadAsync(bytes, 0, bytes.Length);

                var text = Encoding.UTF8.GetString(bytes);
                Console.WriteLine(text);

                if (text.ToLower().StartsWith(connectText))
                {
                    // extract the url and port
                    var host = text.Remove(0, connectText.Length + 1);
                    var hostIndex = host.IndexOf(" ", StringComparison.Ordinal);
                    var hostEntry = host.Remove(hostIndex).Split(new[] { ":" }, StringSplitOptions.None);
                    // connect to the url and prot supplied
                    await requestClient.ConnectAsync(hostEntry[0], Convert.ToInt32(hostEntry[1]));
                    requestStream = requestClient.GetStream();

                    requestStream.ReadTimeout = 100;
                    requestStream.WriteTimeout = 100;

                    // send 200 response to proxyStream 
                    const string sslResponse = "HTTP/1.0 200 Connection established\r\n\r\n";
                    var sslResponseBytes = Encoding.UTF8.GetBytes(sslResponse);
                    await proxyStream.WriteAsync(sslResponseBytes, 0, sslResponseBytes.Length);
                }
            }
            hostHeaderAvailable++;

            CancellationToken cancellationToken = new CancellationToken(false);

            Task task               = proxyStream.CopyToAsync(requestStream, cancellationToken);
            Task task2              = requestStream.CopyToAsync(proxyStream, cancellationToken);
            Task handleConnection   = HandleDisconnect(clt, requestClient, cancellationToken);

            tasks.Add(task);
            tasks.Add(task2);
            tasks.Add(handleConnection);
                
            await Task.WhenAll(tasks).ConfigureAwait(false);

            // close conenctions
            clt.Close();
            clt.Dispose();
            requestClient.Close();
            requestClient.Dispose();
        }
    }
    catch (Exception e)
    {
        Console.WriteLine(e.ToString());
    }
}

UPDATE

Attempt at using CancellationTokenSource

CancellationTokenSource source = new CancellationTokenSource();
CancellationToken cancellationToken = source.Token;
TaskFactory factory = new TaskFactory(cancellationToken);

tasks.Add(factory.StartNew(() => {proxyStream.CopyToAsync(requestStream);}, cancellationToken));
tasks.Add(factory.StartNew(() => {requestStream.CopyToAsync(proxyStream);}, cancellationToken));
tasks.Add(factory.StartNew(async () => {
    //wait for this to retur, then cancel the token
    await HandleDisconnect(clt, requestClient);
    source.Cancel();
}, cancellationToken));

try
{
    await factory.ContinueWhenAll(tasks.ToArray(),
                                                 (results) =>
                                                 {
                                                     Console.WriteLine("Tasks complete");
                                                 }, cancellationToken);
}
catch (AggregateException ae)
{
    foreach (Exception e in ae.InnerExceptions)
    {
        if (e is TaskCanceledException)
            Console.WriteLine("Unable to compute mean: {0}",
                              ((TaskCanceledException)e).Message);
        else
            Console.WriteLine("Exception: " + e.GetType().Name);
    }
}
finally
{
    source.Dispose();
}

UPDATE

public static class extensionTcpClient{

    public static bool CheckIfDisconnected(this TcpClient tcp)
    {
        if (tcp.Client.Poll(0, SelectMode.SelectRead))
        {
            byte[] buff = new byte[1];

            if (tcp.Client.Receive(buff, SocketFlags.Peek) == 0)
            {
                // Client disconnected
                return false;
            }
        }

        return true;
    }
}


class ProxyMaintainer
{

    private static TcpListener listener = new TcpListener(IPAddress.Parse("192.168.0.25"), 13000);

    public ProxyMaintainer()
    {
    }

    public async Task Start()
    {
        Console.WriteLine("###############################");
        Console.WriteLine("Listening on 192.168.0.25:13000");
        Console.WriteLine("###############################\n");

        listener.Start();

        while (listen)
        {
            if (listener.Pending())
            {
                HandleClient(await listener.AcceptTcpClientAsync());
            }
            else
            {
                await Task.Delay(100); //<--- timeout
            }
        }
    }


    private static async Task Transport(NetworkStream from, NetworkStream to, Func<bool> isAlivePoller, CancellationToken token)
    {
        byte[] buffer = new byte[4096];

        while (isAlivePoller())
        {
            while (from.DataAvailable)
            {
                int read = await from.ReadAsync(buffer, 0, buffer.Length, token).ConfigureAwait(false);
                await to.WriteAsync(buffer, 0, read, token);
            }

            // Relieve the CPU a bit.
            await Task.Delay(10, token).ConfigureAwait(false);
        }
    }


    private static async Task HandleClient(TcpClient clientFrom)
    {
        var hostHeaderAvailable = 0;
        int count;
        var bytes = new byte[clientFrom.ReceiveBufferSize];
        const string connectText = "connect";
        NetworkStream toStream = null;

        using (var fromStream = clientFrom.GetStream())
        using(TcpClient clientTo = new TcpClient())
        using (var manualStopper = new CancellationTokenSource())
        {
            count = await fromStream.ReadAsync(bytes, 0, bytes.Length);

            var text = Encoding.UTF8.GetString(bytes);
            Console.WriteLine(text);

            if (text.ToLower().StartsWith(connectText))
            {
                // extract the url and port
                var host = text.Remove(0, connectText.Length + 1);
                var hostIndex = host.IndexOf(" ", StringComparison.Ordinal);
                var hostEntry = host.Remove(hostIndex).Split(new[] { ":" }, StringSplitOptions.None);
                // connect to the url and prot supplied
                await clientTo.ConnectAsync(hostEntry[0], Convert.ToInt32(hostEntry[1]));
                toStream = clientTo.GetStream();

                // send 200 response to proxyStream 
                const string sslResponse = "HTTP/1.0 200 Connection established\r\n\r\n";
                var sslResponseBytes = Encoding.UTF8.GetBytes(sslResponse);
                await fromStream.WriteAsync(sslResponseBytes, 0, sslResponseBytes.Length);
            }
            
            bool Poller() => clientFrom.CheckIfDisconnected() && clientTo.CheckIfDisconnected();

            Task one = Transport(fromStream, toStream, Poller, manualStopper.Token);
            Task two = Transport(toStream, fromStream, Poller, manualStopper.Token);

            await Task.WhenAll(one, two).ConfigureAwait(false);
            //await one; await two; // To get exceptions if you want them and there are any.
            // Alternatively, you can use Task.WhenAll to get exceptions aggregated for you.
        }

        Console.WriteLine("Closing connection");
    }



}

Answer 1

Well, tell you what. The data availability, when it comes to HTTP, lies only in one parameter (if we omit things like WebSocket), which is called Connection and is passed as a Header as a one of two possible states: Close or Keep-Alive.

If Close is chosen by the client, the server is obliged to close the conection as soon as the request is served, whereas Keep-Alive tells the server that, if it doesn't want to, it may leave connection open for another request.

Let's consider both cases.

If client chooses Keep-Alive, the connection will persist and work as intended, indefinetely. But:

If either side drops the connection, there is an easy way to detect that. This piece of code was found on StackOverflow and it was told that it still works perfectly:

public static bool CheckIfDisconnected(this TcpClient tcp)
{
    if (tcp.Client.Poll(0, SelectMode.SelectRead))
    {
        byte[] buff = new byte[1];

        if (tcp.Client.Receive(buff, SocketFlags.Peek) == 0)
        {
            // Client disconnected
            return true;
        }
    }

    return false;
}

So I believe that you, as a proxy-server, are not obliged to manage connection states at all and can leave it to the actual communication parties. All you have to do is to detect when either of your connections - proxy or request - is dropped, drop the other one and call it a day.

P.S. Now, you also asked about asynchronicity.

I must add that TCP connections are considered full-duplex. which means you are free to create two async-running tasks, both reading and writing to their own sinks. My thoughts, it would be the optimal course of action.

Answer 2

To answer your other question

You are still using Stream.CopyToAsync which, as I have told you, is not going to succeed as long as any communicating party decides to wait a bit before sending another chunk of data.

You are also somewhat overcomplicating your solution.

I would put it this way:

async Task Transport(NetworkStream from, NetworkStream to, Func<bool> isAlivePoller, CancellationToken token)
{
    byte[] buffer = new byte[4096];

    while (isAlivePoller())
    {
        while (from.DataAvailable)
        {
            int read = await from.ReadAsync(buffer, 0, buffer.Length, token).ConfigureAwait(false);
            await to.WriteAsync(buffer, 0, read, token).ConfigureAwait(false);
        }

        // Relieve the CPU a bit.
        await Task.Delay(100, token).ConfigureAwait(false);
    }
}

And then in your main code:

using TcpClient clientFrom = ...;
using TcpClient clientTo = ...;
using var fromStream = clientFrom.GetStream();
using var toStream = clientTo.GetStream();
using var manualStopper = new CancellationTokenSource();

bool Poller() => clientFrom.CheckIfDisconnected() && clientTo.CheckIfDisconnected();

Task one = Transport(fromStream, toStream, Poller, stopper.Token);
Task two = Transport(toStream, fromStream, Poller, stopper.Token);

await Task.WhenAny(one, two).ConfigureAwait(false);
//await one; await two; // To get exceptions if you want them and there are any.
// Alternatively, you can use Task.WhenAll to get exceptions aggregated for you.

And you are pretty much done here.