WebSocketSession.cs

// Copyright 2019 Wildbook
// MIT License:
//   Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:
//   The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.
//   THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.

using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Net.Sockets;
using System.Security.Cryptography;
using System.Text;
using System.Text.RegularExpressions;
using System.Threading;
using System.Threading.Tasks;

public class WebSocketSession : IDisposable
{
    private static readonly Random Random = new Random();

    private TcpClient Client { get; }
    private Stream ClientStream { get; }

    public string Id { get; }
    public bool IsMasking { get; private set; }

    public event EventHandler<WebSocketSession> HandshakeCompleted;
    public event EventHandler<WebSocketSession> Disconnected;
    public event EventHandler<Exception> Error;
    public event EventHandler<byte[]> AnyMessageReceived;
    public event EventHandler<string> TextMessageReceived;
    public event EventHandler<byte[]> BinaryMessageReceived;

    public WebSocketSession(TcpClient client)
    {
        Client = client;
        ClientStream = client.GetStream();
        Id = Guid.NewGuid().ToString();
    }

    /// <summary>
    /// Internal, do not use :)
    /// </summary>
    internal void Start()
    {
        ThreadPool.QueueUserWorkItem(_ =>
        {
            if (!DoHandshake())
            {
                Error?.Invoke(this, new Exception("Handshake Failed."));
                Disconnected?.Invoke(this, this);
                return;
            }

            HandshakeCompleted?.Invoke(this, this);
            StartMessageLoop();
        });
    }

    private void StartMessageLoop()
    {
        ThreadPool.QueueUserWorkItem(_ =>
        {
            try
            {
                MessageLoop();
            }
            catch (Exception e)
            {
                Error?.Invoke(this, e);
            }
            finally
            {
                Disconnected?.Invoke(this, this);
            }
        });
    }

    private bool DoHandshake()
    {
        while (Client.Available == 0 && Client.Connected) { }
        if (!Client.Connected) return false;

        byte[] handshake;
        using (var handshakeBuffer = new MemoryStream())
        {
            while (Client.Available > 0)
            {
                var buffer = new byte[Client.Available];
                ClientStream.Read(buffer, 0, buffer.Length);
                handshakeBuffer.Write(buffer, 0, buffer.Length);
            }

            handshake = handshakeBuffer.ToArray();
        }

        if (!Encoding.UTF8.GetString(handshake).StartsWith("GET")) return false;

        var response = Encoding.UTF8.GetBytes("HTTP/1.1 101 Switching Protocols" + Environment.NewLine
                                              + "Connection: Upgrade" + Environment.NewLine
                                              + "Upgrade: websocket" + Environment.NewLine
                                              + "Sec-WebSocket-Accept: " + Convert.ToBase64String(
                                                  SHA1.Create().ComputeHash(
                                                      Encoding.UTF8.GetBytes(
                                                          new Regex("Sec-WebSocket-Key: (.*)").Match(Encoding.UTF8.GetString(handshake)).Groups[1].Value.Trim() + "258EAFA5-E914-47DA-95CA-C5AB0DC85B11"
                                                      )
                                                  )
                                              ) + Environment.NewLine
                                              + Environment.NewLine);

        ClientStream.Write(response, 0, response.Length);
        return true;
    }
    private void MessageLoop()
    {
        var session = this;
        var client = session.Client;
        var stream = session.ClientStream;

        var packet = new List<byte>();

        var messageOpcode = 0x0;
        using (var messageBuffer = new MemoryStream())
            while (client.Connected)
            {
                packet.Clear();

                var ab = client.Available;
                if (ab == 0) continue;

                packet.Add((byte)stream.ReadByte());
                var fin = (packet[0] & (1 << 7)) != 0;
                var rsv1 = (packet[0] & (1 << 6)) != 0;
                var rsv2 = (packet[0] & (1 << 5)) != 0;
                var rsv3 = (packet[0] & (1 << 4)) != 0;

                // Must error if is set.
                //if (rsv1 || rsv2 || rsv3)
                //    return;

                var opcode = packet[0] & ((1 << 4) - 1);

                switch (opcode)
                {
                    case 0x0: // Continuation Frame
                        break;
                    case 0x1: // Text
                    case 0x2: // Binary
                    case 0x8: // Connection Close
                        messageOpcode = opcode;
                        break;
                    case 0x9:
                        continue; // Ping
                    case 0xA:
                        continue; // Pong
                    default:
                        continue; // Reserved
                }

                packet.Add((byte)stream.ReadByte());
                var masked = IsMasking = (packet[1] & (1 << 7)) != 0;
                var pseudoLength = packet[1] - (masked ? 128 : 0);

                ulong actualLength = 0;
                if (pseudoLength > 0 && pseudoLength < 125) actualLength = (ulong)pseudoLength;
                else if (pseudoLength == 126)
                {
                    var length = new byte[2];
                    stream.Read(length, 0, length.Length);
                    packet.AddRange(length);
                    Array.Reverse(length);
                    actualLength = BitConverter.ToUInt16(length, 0);
                }
                else if (pseudoLength == 127)
                {
                    var length = new byte[8];
                    stream.Read(length, 0, length.Length);
                    packet.AddRange(length);
                    Array.Reverse(length);
                    actualLength = BitConverter.ToUInt64(length, 0);
                }

                var mask = new byte[4];
                if (masked)
                {
                    stream.Read(mask, 0, mask.Length);
                    packet.AddRange(mask);
                }

                if (actualLength > 0)
                {
                    var data = new byte[actualLength];
                    stream.Read(data, 0, data.Length);
                    packet.AddRange(data);

                    if (masked)
                        data = ApplyMask(data, mask);

                    messageBuffer.Write(data, 0, data.Length);
                }

                Console.WriteLine($@"RECV: {BitConverter.ToString(packet.ToArray())}");

                if (!fin) continue;
                var message = messageBuffer.ToArray();

                switch (messageOpcode)
                {
                    case 0x1:
                        AnyMessageReceived?.Invoke(session, message);
                        TextMessageReceived?.Invoke(session, Encoding.UTF8.GetString(message));
                        break;
                    case 0x2:
                        AnyMessageReceived?.Invoke(session, message);
                        BinaryMessageReceived?.Invoke(session, message);
                        break;
                    case 0x8:
                        Close();
                        break;
                    default:
                        throw new Exception("Invalid opcode: " + messageOpcode);
                }

                messageBuffer.SetLength(0);
            }
    }

    public void Close()
    {
        if (!Client.Connected) return;

        var mask = new byte[4];
        if (IsMasking) Random.NextBytes(mask);
        SendMessage(new byte[] { }, 0x8, IsMasking, mask);
        
        Client.Close();
    }

    public void SendMessage(string payload) => SendMessage(Client, payload, IsMasking);
    public void SendMessage(byte[] payload, bool isBinary = false) => SendMessage(Client, payload, isBinary, IsMasking);

    public void SendMessage(byte[] payload, bool isBinary = false, bool masking = false) => SendMessage(Client, payload, isBinary, masking);
    public void SendMessage(byte[] payload, int opcode, bool masking, byte[] mask) => SendMessage(Client, payload, opcode, masking, mask);

    static void SendMessage(TcpClient client, string payload, bool masking = false) =>
                SendMessage(client, Encoding.UTF8.GetBytes(payload), false, masking);
    static void SendMessage(TcpClient client, byte[] payload, bool isBinary = false, bool masking = false)
    {
        var mask = new byte[4];
        if (masking) Random.NextBytes(mask);
        SendMessage(client, payload, isBinary ? 0x2 : 0x1, masking, mask);
    }
    static void SendMessage(TcpClient client, byte[] payload, int opcode, bool masking, byte[] mask)
    {
        if (masking && mask == null) throw new ArgumentException(nameof(mask));

        using (var packet = new MemoryStream())
        {
            byte firstbyte = 0b0_0_0_0_0000; // fin | rsv1 | rsv2 | rsv3 | [ OPCODE | OPCODE | OPCODE | OPCODE ]

            firstbyte |= 0b1_0_0_0_0000; // fin
            //firstbyte |= 0b0_1_0_0_0000; // rsv1
            //firstbyte |= 0b0_0_1_0_0000; // rsv2
            //firstbyte |= 0b0_0_0_1_0000; // rsv3

            firstbyte += (byte)opcode; // Text
            packet.WriteByte(firstbyte);

            // Set bit: bytes[byteIndex] |= mask;

            byte secondbyte = 0b0_0000000; // mask | [SIZE | SIZE  | SIZE  | SIZE  | SIZE  | SIZE | SIZE]

            if (masking)
                secondbyte |= 0b1_0000000; // mask

            if (payload.LongLength <= 0b0_1111101) // 125
            {
                secondbyte |= (byte)payload.Length;
                packet.WriteByte(secondbyte);
            }
            else if (payload.LongLength <= UInt16.MaxValue) // If length takes 2 bytes
            {
                secondbyte |= 0b0_1111110; // 126
                packet.WriteByte(secondbyte);

                var len = BitConverter.GetBytes(payload.LongLength);
                Array.Reverse(len, 0, 2);
                packet.Write(len, 0, 2);
            }
            else // if (payload.LongLength <= Int64.MaxValue) // If length takes 8 bytes
            {
                secondbyte |= 0b0_1111111; // 127
                packet.WriteByte(secondbyte);

                var len = BitConverter.GetBytes(payload.LongLength);
                Array.Reverse(len, 0, 8);
                packet.Write(len, 0, 8);
            }

            if (masking)
            {
                packet.Write(mask, 0, 4);
                payload = ApplyMask(payload, mask);
            }

            // Write all data to the packet
            packet.Write(payload, 0, payload.Length);

            // Get client's stream
            var stream = client.GetStream();

            var finalPacket = packet.ToArray();
            Console.WriteLine($@"SENT: {BitConverter.ToString(finalPacket)}");

            // Send the packet
            foreach (var b in finalPacket)
                stream.WriteByte(b);
        }
    }

    static byte[] ApplyMask(IReadOnlyList<byte> msg, IReadOnlyList<byte> mask)
    {
        var decoded = new byte[msg.Count];
        for (var i = 0; i < msg.Count; i++)
            decoded[i] = (byte)(msg[i] ^ mask[i % 4]);
        return decoded;
    }

    public void Dispose()
    {
        Close();

        ((IDisposable)Client)?.Dispose();
        ClientStream?.Dispose();
    }
}