/// <summary>
        /// This is called when this proxy acts as a reverse proxy (like a real http server)
        /// So for HTTPS requests we would start SSL negotiation right away without expecting a CONNECT request from client
        /// </summary>
        /// <param name="endPoint"></param>
        /// <param name="tcpClient"></param>
        /// <returns></returns>
        private async Task HandleClient(TransparentProxyEndPoint endPoint, TcpClient tcpClient)
        {
            var clientStream = new CustomBufferedStream(tcpClient.GetStream(), BufferSize);

            var clientStreamReader = new CustomBinaryReader(clientStream, BufferSize);
            var clientStreamWriter = new HttpResponseWriter(clientStream, BufferSize);

            try
            {
                if (endPoint.EnableSsl)
                {
                    var clientHelloInfo = await SslTools.PeekClientHello(clientStream);

                    if (clientHelloInfo != null)
                    {
                        var sslStream = new SslStream(clientStream);
                        clientStream = new CustomBufferedStream(sslStream, BufferSize);

                        string sniHostName = clientHelloInfo.GetServerName() ?? endPoint.GenericCertificateName;

                        string certName    = HttpHelper.GetWildCardDomainName(sniHostName);
                        var    certificate = await CertificateManager.CreateCertificateAsync(certName);

                        try
                        {
                            //Successfully managed to authenticate the client using the fake certificate
                            await sslStream.AuthenticateAsServerAsync(certificate, false, SslProtocols.Tls, false);
                        }
                        catch (Exception e)
                        {
                            ExceptionFunc(new Exception($"Could'nt authenticate client '{sniHostName}' with fake certificate.", e));
                            return;
                        }
                    }

                    //HTTPS server created - we can now decrypt the client's traffic
                }

                //Now create the request
                await HandleHttpSessionRequest(tcpClient, clientStream, clientStreamReader, clientStreamWriter,
                                               endPoint.EnableSsl?endPoint.GenericCertificateName : null, endPoint, null, true);
            }
            finally
            {
                clientStreamReader.Dispose();
                clientStream.Dispose();
            }
        }
        /// <summary>
        ///     This is called when this proxy acts as a reverse proxy (like a real http server).
        ///     So for HTTPS requests we would start SSL negotiation right away without expecting a CONNECT request from client
        /// </summary>
        /// <param name="endPoint">The transparent endpoint.</param>
        /// <param name="clientConnection">The client connection.</param>
        /// <returns></returns>
        private async Task handleClient(TransparentProxyEndPoint endPoint, TcpClientConnection clientConnection)
        {
            var cancellationTokenSource = new CancellationTokenSource();
            var cancellationToken       = cancellationTokenSource.Token;

            var clientStream       = new CustomBufferedStream(clientConnection.GetStream(), BufferPool, BufferSize);
            var clientStreamWriter = new HttpResponseWriter(clientStream, BufferPool, BufferSize);

            Task <TcpServerConnection> prefetchConnectionTask = null;
            bool closeServerConnection = false;
            bool calledRequestHandler  = false;

            try
            {
                var clientHelloInfo = await SslTools.PeekClientHello(clientStream, BufferPool, cancellationToken);

                bool   isHttps       = clientHelloInfo != null;
                string httpsHostName = null;

                if (isHttps)
                {
                    httpsHostName = clientHelloInfo.GetServerName() ?? endPoint.GenericCertificateName;

                    var args = new BeforeSslAuthenticateEventArgs(cancellationTokenSource)
                    {
                        SniHostName = httpsHostName
                    };

                    await endPoint.InvokeBeforeSslAuthenticate(this, args, ExceptionFunc);

                    if (cancellationTokenSource.IsCancellationRequested)
                    {
                        throw new Exception("Session was terminated by user.");
                    }

                    if (endPoint.DecryptSsl && args.DecryptSsl)
                    {
                        if (EnableTcpServerConnectionPrefetch)
                        {
                            //don't pass cancellation token here
                            //it could cause floating server connections when client exits
                            prefetchConnectionTask = tcpConnectionFactory.GetServerConnection(httpsHostName, endPoint.Port,
                                                                                              httpVersion: null, isHttps: true, applicationProtocols: null, isConnect: false,
                                                                                              proxyServer: this, session: null, upStreamEndPoint: UpStreamEndPoint, externalProxy: UpStreamHttpsProxy,
                                                                                              noCache: false, cancellationToken: CancellationToken.None);
                        }

                        SslStream sslStream = null;

                        //do client authentication using fake certificate
                        try
                        {
                            sslStream = new SslStream(clientStream);

                            string certName    = HttpHelper.GetWildCardDomainName(httpsHostName);
                            var    certificate = endPoint.GenericCertificate ??
                                                 await CertificateManager.CreateCertificateAsync(certName);

                            // Successfully managed to authenticate the client using the fake certificate
                            await sslStream.AuthenticateAsServerAsync(certificate, false, SslProtocols.Tls, false);

                            // HTTPS server created - we can now decrypt the client's traffic
                            clientStream = new CustomBufferedStream(sslStream, BufferPool, BufferSize);

                            clientStreamWriter = new HttpResponseWriter(clientStream, BufferPool, BufferSize);
                        }
                        catch (Exception e)
                        {
                            sslStream?.Dispose();
                            throw new ProxyConnectException(
                                      $"Could'nt authenticate client '{httpsHostName}' with fake certificate.", e, null);
                        }
                    }
                    else
                    {
                        var connection = await tcpConnectionFactory.GetServerConnection(httpsHostName, endPoint.Port,
                                                                                        httpVersion : null, isHttps : false, applicationProtocols : null,
                                                                                        isConnect : true, proxyServer : this, session : null, upStreamEndPoint : UpStreamEndPoint,
                                                                                        externalProxy : UpStreamHttpsProxy, noCache : true, cancellationToken : cancellationToken);

                        try
                        {
                            CustomBufferedStream serverStream = null;
                            int available = clientStream.Available;

                            if (available > 0)
                            {
                                // send the buffered data
                                var data = BufferPool.GetBuffer(BufferSize);
                                try
                                {
                                    // clientStream.Available sbould be at most BufferSize because it is using the same buffer size
                                    await clientStream.ReadAsync(data, 0, available, cancellationToken);

                                    serverStream = connection.Stream;
                                    await serverStream.WriteAsync(data, 0, available, cancellationToken);

                                    await serverStream.FlushAsync(cancellationToken);
                                }
                                finally
                                {
                                    BufferPool.ReturnBuffer(data);
                                }
                            }

                            await TcpHelper.SendRaw(clientStream, serverStream, BufferPool, BufferSize,
                                                    null, null, cancellationTokenSource, ExceptionFunc);
                        }
                        finally
                        {
                            await tcpConnectionFactory.Release(connection, true);
                        }

                        return;
                    }
                }
                calledRequestHandler = true;
                // HTTPS server created - we can now decrypt the client's traffic
                // Now create the request
                await handleHttpSessionRequest(endPoint, clientConnection, clientStream, clientStreamWriter,
                                               cancellationTokenSource, isHttps?httpsHostName : null, null, prefetchConnectionTask);
            }
            catch (ProxyException e)
            {
                closeServerConnection = true;
                onException(clientStream, e);
            }
            catch (IOException e)
            {
                closeServerConnection = true;
                onException(clientStream, new Exception("Connection was aborted", e));
            }
            catch (SocketException e)
            {
                closeServerConnection = true;
                onException(clientStream, new Exception("Could not connect", e));
            }
            catch (Exception e)
            {
                closeServerConnection = true;
                onException(clientStream, new Exception("Error occured in whilst handling the client", e));
            }
            finally
            {
                if (!calledRequestHandler)
                {
                    await tcpConnectionFactory.Release(prefetchConnectionTask, closeServerConnection);
                }

                clientStream.Dispose();

                if (!cancellationTokenSource.IsCancellationRequested)
                {
                    cancellationTokenSource.Cancel();
                }
            }
        }
Example #3
0
        /// <summary>
        ///     This is called when client is aware of proxy
        ///     So for HTTPS requests client would send CONNECT header to negotiate a secure tcp tunnel via proxy
        /// </summary>
        /// <param name="endPoint">The explicit endpoint.</param>
        /// <param name="clientConnection">The client connection.</param>
        /// <returns>The task.</returns>
        private async Task handleClient(ExplicitProxyEndPoint endPoint, TcpClientConnection clientConnection)
        {
            var cancellationTokenSource = new CancellationTokenSource();
            var cancellationToken       = cancellationTokenSource.Token;

            var clientStream       = new CustomBufferedStream(clientConnection.GetStream(), BufferPool, BufferSize);
            var clientStreamWriter = new HttpResponseWriter(clientStream, BufferPool, BufferSize);

            Task <TcpServerConnection> prefetchConnectionTask = null;
            bool closeServerConnection = false;
            bool calledRequestHandler  = false;

            try
            {
                string connectHostname = null;
                TunnelConnectSessionEventArgs connectArgs = null;


                // Client wants to create a secure tcp tunnel (probably its a HTTPS or Websocket request)
                if (await HttpHelper.IsConnectMethod(clientStream) == 1)
                {
                    // read the first line HTTP command
                    string httpCmd = await clientStream.ReadLineAsync(cancellationToken);

                    if (string.IsNullOrEmpty(httpCmd))
                    {
                        return;
                    }

                    Request.ParseRequestLine(httpCmd, out string _, out string httpUrl, out var version);

                    var httpRemoteUri = new Uri("http://" + httpUrl);
                    connectHostname = httpRemoteUri.Host;

                    var connectRequest = new ConnectRequest
                    {
                        RequestUri  = httpRemoteUri,
                        OriginalUrl = httpUrl,
                        HttpVersion = version
                    };

                    await HeaderParser.ReadHeaders(clientStream, connectRequest.Headers, cancellationToken);

                    connectArgs = new TunnelConnectSessionEventArgs(this, endPoint, connectRequest,
                                                                    cancellationTokenSource);
                    connectArgs.ProxyClient.ClientConnection = clientConnection;
                    connectArgs.ProxyClient.ClientStream     = clientStream;

                    await endPoint.InvokeBeforeTunnelConnectRequest(this, connectArgs, ExceptionFunc);

                    // filter out excluded host names
                    bool decryptSsl = endPoint.DecryptSsl && connectArgs.DecryptSsl;

                    if (connectArgs.DenyConnect)
                    {
                        if (connectArgs.WebSession.Response.StatusCode == 0)
                        {
                            connectArgs.WebSession.Response = new Response
                            {
                                HttpVersion       = HttpHeader.Version11,
                                StatusCode        = (int)HttpStatusCode.Forbidden,
                                StatusDescription = "Forbidden"
                            };
                        }

                        // send the response
                        await clientStreamWriter.WriteResponseAsync(connectArgs.WebSession.Response,
                                                                    cancellationToken : cancellationToken);

                        return;
                    }

                    if (await checkAuthorization(connectArgs) == false)
                    {
                        await endPoint.InvokeBeforeTunnectConnectResponse(this, connectArgs, ExceptionFunc);

                        // send the response
                        await clientStreamWriter.WriteResponseAsync(connectArgs.WebSession.Response,
                                                                    cancellationToken : cancellationToken);

                        return;
                    }

                    // write back successfull CONNECT response
                    var response = ConnectResponse.CreateSuccessfullConnectResponse(version);

                    // Set ContentLength explicitly to properly handle HTTP 1.0
                    response.ContentLength = 0;
                    response.Headers.FixProxyHeaders();
                    connectArgs.WebSession.Response = response;

                    await clientStreamWriter.WriteResponseAsync(response, cancellationToken : cancellationToken);

                    var clientHelloInfo = await SslTools.PeekClientHello(clientStream, BufferPool, cancellationToken);

                    bool isClientHello = clientHelloInfo != null;
                    if (isClientHello)
                    {
                        connectRequest.ClientHelloInfo = clientHelloInfo;
                    }

                    await endPoint.InvokeBeforeTunnectConnectResponse(this, connectArgs, ExceptionFunc, isClientHello);

                    if (decryptSsl && isClientHello)
                    {
                        connectRequest.RequestUri = new Uri("https://" + httpUrl);

                        bool http2Supported = false;

                        var alpn = clientHelloInfo.GetAlpn();
                        if (alpn != null && alpn.Contains(SslApplicationProtocol.Http2))
                        {
                            // test server HTTP/2 support
                            // todo: this is a hack, because Titanium does not support HTTP protocol changing currently
                            var connection = await tcpConnectionFactory.GetServerConnection(this, connectArgs,
                                                                                            isConnect : true, applicationProtocols : SslExtensions.Http2ProtocolAsList,
                                                                                            noCache : true, cancellationToken : cancellationToken);

                            http2Supported = connection.NegotiatedApplicationProtocol == SslApplicationProtocol.Http2;

                            //release connection back to pool intead of closing when connection pool is enabled.
                            await tcpConnectionFactory.Release(connection, true);
                        }

                        SslStream sslStream = null;

                        //don't pass cancellation token here
                        //it could cause floating server connections when client exits
                        prefetchConnectionTask = tcpConnectionFactory.GetServerConnection(this, connectArgs,
                                                                                          isConnect: true, applicationProtocols: null, noCache: false,
                                                                                          cancellationToken: CancellationToken.None);

                        try
                        {
                            sslStream = new SslStream(clientStream);

                            string certName = HttpHelper.GetWildCardDomainName(connectHostname);

                            var certificate = endPoint.GenericCertificate ??
                                              await CertificateManager.CreateCertificateAsync(certName);

                            // Successfully managed to authenticate the client using the fake certificate
                            var options = new SslServerAuthenticationOptions();
                            if (http2Supported)
                            {
                                options.ApplicationProtocols = clientHelloInfo.GetAlpn();
                                if (options.ApplicationProtocols == null || options.ApplicationProtocols.Count == 0)
                                {
                                    options.ApplicationProtocols = SslExtensions.Http11ProtocolAsList;
                                }
                            }

                            options.ServerCertificate              = certificate;
                            options.ClientCertificateRequired      = false;
                            options.EnabledSslProtocols            = SupportedSslProtocols;
                            options.CertificateRevocationCheckMode = X509RevocationMode.NoCheck;
                            await sslStream.AuthenticateAsServerAsync(options, cancellationToken);

#if NETCOREAPP2_1
                            clientConnection.NegotiatedApplicationProtocol = sslStream.NegotiatedApplicationProtocol;
#endif

                            // HTTPS server created - we can now decrypt the client's traffic
                            clientStream       = new CustomBufferedStream(sslStream, BufferPool, BufferSize);
                            clientStreamWriter = new HttpResponseWriter(clientStream, BufferPool, BufferSize);
                        }
                        catch (Exception e)
                        {
                            sslStream?.Dispose();
                            throw new ProxyConnectException(
                                      $"Could'nt authenticate client '{connectHostname}' with fake certificate.", e, connectArgs);
                        }

                        if (await HttpHelper.IsConnectMethod(clientStream) == -1)
                        {
                            decryptSsl = false;
                        }
                    }

                    if (cancellationTokenSource.IsCancellationRequested)
                    {
                        throw new Exception("Session was terminated by user.");
                    }

                    // Hostname is excluded or it is not an HTTPS connect
                    if (!decryptSsl || !isClientHello)
                    {
                        // create new connection to server.
                        // If we detected that client tunnel CONNECTs without SSL by checking for empty client hello then
                        // this connection should not be HTTPS.
                        var connection = await tcpConnectionFactory.GetServerConnection(this, connectArgs,
                                                                                        isConnect : true, applicationProtocols : SslExtensions.Http2ProtocolAsList,
                                                                                        noCache : true, cancellationToken : cancellationToken);

                        try
                        {
                            if (isClientHello)
                            {
                                int available = clientStream.Available;
                                if (available > 0)
                                {
                                    // send the buffered data
                                    var data = BufferPool.GetBuffer(BufferSize);

                                    try
                                    {
                                        await clientStream.ReadAsync(data, 0, available, cancellationToken);

                                        // clientStream.Available sbould be at most BufferSize because it is using the same buffer size
                                        await connection.StreamWriter.WriteAsync(data, 0, available, true, cancellationToken);
                                    }
                                    finally
                                    {
                                        BufferPool.ReturnBuffer(data);
                                    }
                                }

                                var serverHelloInfo = await SslTools.PeekServerHello(connection.Stream, BufferPool, cancellationToken);

                                ((ConnectResponse)connectArgs.WebSession.Response).ServerHelloInfo = serverHelloInfo;
                            }

                            await TcpHelper.SendRaw(clientStream, connection.Stream, BufferPool, BufferSize,
                                                    (buffer, offset, count) => { connectArgs.OnDataSent(buffer, offset, count); },
                                                    (buffer, offset, count) => { connectArgs.OnDataReceived(buffer, offset, count); },
                                                    connectArgs.CancellationTokenSource, ExceptionFunc);
                        }
                        finally
                        {
                            await tcpConnectionFactory.Release(connection, true);
                        }

                        return;
                    }
                }

                if (connectArgs != null && await HttpHelper.IsPriMethod(clientStream) == 1)
                {
                    // todo
                    string httpCmd = await clientStream.ReadLineAsync(cancellationToken);

                    if (httpCmd == "PRI * HTTP/2.0")
                    {
                        // HTTP/2 Connection Preface
                        string line = await clientStream.ReadLineAsync(cancellationToken);

                        if (line != string.Empty)
                        {
                            throw new Exception($"HTTP/2 Protocol violation. Empty string expected, '{line}' received");
                        }

                        line = await clientStream.ReadLineAsync(cancellationToken);

                        if (line != "SM")
                        {
                            throw new Exception($"HTTP/2 Protocol violation. 'SM' expected, '{line}' received");
                        }

                        line = await clientStream.ReadLineAsync(cancellationToken);

                        if (line != string.Empty)
                        {
                            throw new Exception($"HTTP/2 Protocol violation. Empty string expected, '{line}' received");
                        }

                        var connection = await tcpConnectionFactory.GetServerConnection(this, connectArgs,
                                                                                        isConnect : true, applicationProtocols : SslExtensions.Http2ProtocolAsList,
                                                                                        noCache : true, cancellationToken : cancellationToken);

                        try
                        {
                            await connection.StreamWriter.WriteLineAsync("PRI * HTTP/2.0", cancellationToken);

                            await connection.StreamWriter.WriteLineAsync(cancellationToken);

                            await connection.StreamWriter.WriteLineAsync("SM", cancellationToken);

                            await connection.StreamWriter.WriteLineAsync(cancellationToken);

#if NETCOREAPP2_1
                            await Http2Helper.SendHttp2(clientStream, connection.Stream, BufferSize,
                                                        (buffer, offset, count) => { connectArgs.OnDataSent(buffer, offset, count); },
                                                        (buffer, offset, count) => { connectArgs.OnDataReceived(buffer, offset, count); },
                                                        connectArgs.CancellationTokenSource, clientConnection.Id, ExceptionFunc);
#endif
                        }
                        finally
                        {
                            await tcpConnectionFactory.Release(connection, true);
                        }
                    }
                }

                calledRequestHandler = true;
                // Now create the request
                await handleHttpSessionRequest(endPoint, clientConnection, clientStream, clientStreamWriter,
                                               cancellationTokenSource, connectHostname, connectArgs?.WebSession.ConnectRequest, prefetchConnectionTask);
            }
            catch (ProxyException e)
            {
                closeServerConnection = true;
                onException(clientStream, e);
            }
            catch (IOException e)
            {
                closeServerConnection = true;
                onException(clientStream, new Exception("Connection was aborted", e));
            }
            catch (SocketException e)
            {
                closeServerConnection = true;
                onException(clientStream, new Exception("Could not connect", e));
            }
            catch (Exception e)
            {
                closeServerConnection = true;
                onException(clientStream, new Exception("Error occured in whilst handling the client", e));
            }
            finally
            {
                if (!calledRequestHandler)
                {
                    await tcpConnectionFactory.Release(prefetchConnectionTask, closeServerConnection);
                }

                clientStream.Dispose();

                if (!cancellationTokenSource.IsCancellationRequested)
                {
                    cancellationTokenSource.Cancel();
                }
            }
        }
        /// <summary>
        /// This is called when client is aware of proxy
        /// So for HTTPS requests client would send CONNECT header to negotiate a secure tcp tunnel via proxy
        /// </summary>
        /// <param name="endPoint"></param>
        /// <param name="tcpClient"></param>
        /// <returns></returns>
        private async Task HandleClient(ExplicitProxyEndPoint endPoint, TcpClient tcpClient)
        {
            var clientStream = new CustomBufferedStream(tcpClient.GetStream(), BufferSize);

            var clientStreamReader = new CustomBinaryReader(clientStream, BufferSize);
            var clientStreamWriter = new HttpResponseWriter(clientStream, BufferSize);

            try
            {
                string connectHostname = null;

                ConnectRequest connectRequest = null;

                //Client wants to create a secure tcp tunnel (probably its a HTTPS or Websocket request)
                if (await HttpHelper.IsConnectMethod(clientStream) == 1)
                {
                    //read the first line HTTP command
                    string httpCmd = await clientStreamReader.ReadLineAsync();

                    if (string.IsNullOrEmpty(httpCmd))
                    {
                        return;
                    }

                    Request.ParseRequestLine(httpCmd, out string _, out string httpUrl, out var version);

                    var httpRemoteUri = new Uri("http://" + httpUrl);
                    connectHostname = httpRemoteUri.Host;

                    //filter out excluded host names
                    bool excluded = false;

                    if (endPoint.ExcludedHttpsHostNameRegex != null)
                    {
                        excluded = endPoint.ExcludedHttpsHostNameRegexList.Any(x => x.IsMatch(connectHostname));
                    }

                    if (endPoint.IncludedHttpsHostNameRegex != null)
                    {
                        excluded = !endPoint.IncludedHttpsHostNameRegexList.Any(x => x.IsMatch(connectHostname));
                    }

                    if (endPoint.BeforeTunnelConnect != null)
                    {
                        excluded = await endPoint.BeforeTunnelConnect(connectHostname);
                    }

                    connectRequest = new ConnectRequest
                    {
                        RequestUri  = httpRemoteUri,
                        OriginalUrl = httpUrl,
                        HttpVersion = version,
                    };

                    await HeaderParser.ReadHeaders(clientStreamReader, connectRequest.Headers);

                    var connectArgs = new TunnelConnectSessionEventArgs(BufferSize, endPoint, connectRequest, ExceptionFunc);
                    connectArgs.ProxyClient.TcpClient    = tcpClient;
                    connectArgs.ProxyClient.ClientStream = clientStream;

                    await endPoint.InvokeTunnectConnectRequest(this, connectArgs, ExceptionFunc);


                    if (await CheckAuthorization(clientStreamWriter, connectArgs) == false)
                    {
                        await endPoint.InvokeTunnectConnectResponse(this, connectArgs, ExceptionFunc);

                        return;
                    }

                    //write back successfull CONNECT response
                    var response = ConnectResponse.CreateSuccessfullConnectResponse(version);
                    response.Headers.FixProxyHeaders();
                    connectArgs.WebSession.Response = response;

                    await clientStreamWriter.WriteResponseAsync(response);

                    var clientHelloInfo = await SslTools.PeekClientHello(clientStream);

                    bool isClientHello = clientHelloInfo != null;
                    if (isClientHello)
                    {
                        connectRequest.ClientHelloInfo = clientHelloInfo;
                    }

                    await endPoint.InvokeTunnectConnectResponse(this, connectArgs, ExceptionFunc, isClientHello);

                    if (!excluded && isClientHello)
                    {
                        connectRequest.RequestUri = new Uri("https://" + httpUrl);

                        SslStream sslStream = null;

                        try
                        {
                            sslStream = new SslStream(clientStream);

                            string certName = HttpHelper.GetWildCardDomainName(connectHostname);

                            var certificate = endPoint.GenericCertificate ?? await CertificateManager.CreateCertificateAsync(certName);

                            //Successfully managed to authenticate the client using the fake certificate
                            await sslStream.AuthenticateAsServerAsync(certificate, false, SupportedSslProtocols, false);

                            //HTTPS server created - we can now decrypt the client's traffic
                            clientStream = new CustomBufferedStream(sslStream, BufferSize);

                            clientStreamReader.Dispose();
                            clientStreamReader = new CustomBinaryReader(clientStream, BufferSize);
                            clientStreamWriter = new HttpResponseWriter(clientStream, BufferSize);
                        }
                        catch
                        {
                            sslStream?.Dispose();
                            return;
                        }

                        if (await HttpHelper.IsConnectMethod(clientStream) == -1)
                        {
                            // It can be for example some Google (Cloude Messaging for Chrome) magic
                            excluded = true;
                        }
                    }

                    //Hostname is excluded or it is not an HTTPS connect
                    if (excluded || !isClientHello)
                    {
                        //create new connection
                        using (var connection = await GetServerConnection(connectArgs, true))
                        {
                            if (isClientHello)
                            {
                                int available = clientStream.Available;
                                if (available > 0)
                                {
                                    //send the buffered data
                                    var data = BufferPool.GetBuffer(BufferSize);

                                    try
                                    {
                                        // clientStream.Available sbould be at most BufferSize because it is using the same buffer size
                                        await clientStream.ReadAsync(data, 0, available);

                                        await connection.StreamWriter.WriteAsync(data, 0, available, true);
                                    }
                                    finally
                                    {
                                        BufferPool.ReturnBuffer(data);
                                    }
                                }

                                var serverHelloInfo = await SslTools.PeekServerHello(connection.Stream);

                                ((ConnectResponse)connectArgs.WebSession.Response).ServerHelloInfo = serverHelloInfo;
                            }

                            await TcpHelper.SendRaw(clientStream, connection.Stream, BufferSize,
                                                    (buffer, offset, count) => { connectArgs.OnDataSent(buffer, offset, count); },
                                                    (buffer, offset, count) => { connectArgs.OnDataReceived(buffer, offset, count); },
                                                    ExceptionFunc);
                        }

                        return;
                    }
                }

                //Now create the request
                await HandleHttpSessionRequest(tcpClient, clientStream, clientStreamReader, clientStreamWriter, connectHostname, endPoint, connectRequest);
            }
            catch (ProxyHttpException e)
            {
                ExceptionFunc(e);
            }
            catch (IOException e)
            {
                ExceptionFunc(new Exception("Connection was aborted", e));
            }
            catch (SocketException e)
            {
                ExceptionFunc(new Exception("Could not connect", e));
            }
            catch (Exception e)
            {
                ExceptionFunc(new Exception("Error occured in whilst handling the client", e));
            }
            finally
            {
                clientStreamReader.Dispose();
                clientStream.Dispose();
            }
        }
        /// <summary>
        ///     This is called when this proxy acts as a reverse proxy (like a real http server).
        ///     So for HTTPS requests we would start SSL negotiation right away without expecting a CONNECT request from client
        /// </summary>
        /// <param name="endPoint">The transparent endpoint.</param>
        /// <param name="clientConnection">The client connection.</param>
        /// <returns></returns>
        private async Task HandleClient(TransparentProxyEndPoint endPoint, TcpClientConnection clientConnection)
        {
            var cancellationTokenSource = new CancellationTokenSource();
            var cancellationToken       = cancellationTokenSource.Token;

            var clientStream = new CustomBufferedStream(clientConnection.GetStream(), BufferSize);

            var clientStreamWriter = new HttpResponseWriter(clientStream, BufferSize);

            try
            {
                var clientHelloInfo = await SslTools.PeekClientHello(clientStream, cancellationToken);

                bool   isHttps       = clientHelloInfo != null;
                string httpsHostName = null;

                if (isHttps)
                {
                    httpsHostName = clientHelloInfo.GetServerName() ?? endPoint.GenericCertificateName;

                    var args = new BeforeSslAuthenticateEventArgs(cancellationTokenSource)
                    {
                        SniHostName = httpsHostName
                    };

                    await endPoint.InvokeBeforeSslAuthenticate(this, args, ExceptionFunc);

                    if (cancellationTokenSource.IsCancellationRequested)
                    {
                        throw new Exception("Session was terminated by user.");
                    }

                    if (endPoint.DecryptSsl && args.DecryptSsl)
                    {
                        SslStream sslStream = null;

                        try
                        {
                            sslStream = new SslStream(clientStream);

                            string certName    = HttpHelper.GetWildCardDomainName(httpsHostName);
                            var    certificate = await CertificateManager.CreateCertificateAsync(certName);

                            // Successfully managed to authenticate the client using the fake certificate
                            await sslStream.AuthenticateAsServerAsync(certificate, false, SslProtocols.Tls, false);

                            // HTTPS server created - we can now decrypt the client's traffic
                            clientStream = new CustomBufferedStream(sslStream, BufferSize);

                            clientStreamWriter = new HttpResponseWriter(clientStream, BufferSize);
                        }
                        catch (Exception e)
                        {
                            sslStream?.Dispose();
                            throw new ProxyConnectException(
                                      $"Could'nt authenticate client '{httpsHostName}' with fake certificate.", e, null);
                        }
                    }
                    else
                    {
                        // create new connection
                        var connection = await tcpConnectionFactory.GetClient(httpsHostName, endPoint.Port,
                                                                              null, false, null,
                                                                              true, this, UpStreamEndPoint, UpStreamHttpsProxy, cancellationToken);


                        var serverStream = connection.Stream;

                        int available = clientStream.Available;
                        if (available > 0)
                        {
                            // send the buffered data
                            var data = BufferPool.GetBuffer(BufferSize);

                            try
                            {
                                // clientStream.Available sbould be at most BufferSize because it is using the same buffer size
                                await clientStream.ReadAsync(data, 0, available, cancellationToken);

                                await serverStream.WriteAsync(data, 0, available, cancellationToken);

                                await serverStream.FlushAsync(cancellationToken);
                            }
                            finally
                            {
                                BufferPool.ReturnBuffer(data);
                            }
                        }

                        await TcpHelper.SendRaw(clientStream, serverStream, BufferSize,
                                                null, null, cancellationTokenSource, ExceptionFunc);

                        tcpConnectionFactory.Release(connection, true);
                        return;
                    }
                }

                // HTTPS server created - we can now decrypt the client's traffic
                // Now create the request
                await HandleHttpSessionRequest(endPoint, clientConnection, clientStream, clientStreamWriter,
                                               cancellationTokenSource, isHttps?httpsHostName : null, null);
            }
            catch (ProxyException e)
            {
                OnException(clientStream, e);
            }
            catch (IOException e)
            {
                OnException(clientStream, new Exception("Connection was aborted", e));
            }
            catch (SocketException e)
            {
                OnException(clientStream, new Exception("Could not connect", e));
            }
            catch (Exception e)
            {
                OnException(clientStream, new Exception("Error occured in whilst handling the client", e));
            }
            finally
            {
                clientStream.Dispose();
                if (!cancellationTokenSource.IsCancellationRequested)
                {
                    cancellationTokenSource.Cancel();
                }
            }
        }