WebSocket Server Vb.NET

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The following sample is not optimized. It does not make use of .NET 4.5 Websocket support.

The current version:

  • contains A Generic Collection of a class that wraps System.Net.Sockets.TcpClient
  • features Custom Events and Delegate Handlers
  • features Threading and implements Timers.Timer
  • demonstrates how to write a frame back to the client using the Network Stream (opCode 0001)
  • is intended to be a starting point for this tutorial and for other contributors


Imports System.Net.Sockets
Imports System.Net
Imports System
Imports System.Text
Imports System.Text.RegularExpressions

Namespace TypeDef.WebSocket

    Public Class Client
        Dim _TcpClient As System.Net.Sockets.TcpClient

        Public Delegate Sub OnClientDisconnectDelegateHandler()
        Public Event onClientDisconnect As OnClientDisconnectDelegateHandler

        Sub New(ByVal tcpClient As System.Net.Sockets.TcpClient)
            Me._TcpClient = tcpClient
        End Sub

        Function isConnected() As Boolean
            Return Me._TcpClient.Connected
        End Function

        Sub HandShake()
            Dim stream As NetworkStream = Me._TcpClient.GetStream()
            Dim bytes As Byte()
            Dim data As String

            While Me._TcpClient.Connected
                While (stream.DataAvailable)
                    ReDim bytes(Me._TcpClient.Client.Available)
                    stream.Read(bytes, 0, bytes.Length)
                    data = System.Text.Encoding.UTF8.GetString(bytes)

                    If (New System.Text.RegularExpressions.Regex("^GET").IsMatch(data)) Then

                        Dim response As Byte() = System.Text.Encoding.UTF8.GetBytes("HTTP/1.1 101 Switching Protocols" & Environment.NewLine & "Connection: Upgrade" & Environment.NewLine & "Upgrade: websocket" & Environment.NewLine & "Sec-WebSocket-Accept: " & Convert.ToBase64String(System.Security.Cryptography.SHA1.Create().ComputeHash(Encoding.UTF8.GetBytes(New Regex("Sec-WebSocket-Key: (.*)").Match(data).Groups(1).Value.Trim() & "258EAFA5-E914-47DA-95CA-C5AB0DC85B11"))) & Environment.NewLine & Environment.NewLine)

                        stream.Write(response, 0, response.Length)
                        Exit Sub
                        'We're going to disconnect the client here, because he's not handshacking properly (or at least to the scope of this code sample)
                        Me._TcpClient.Close() 'The next While Me._TcpClient.Connected Loop Check should fail.. and raise the onClientDisconnect Event Thereafter
                    End If
                End While
            End While
            RaiseEvent onClientDisconnect()
        End Sub

        Sub CheckForDataAvailability()
            If (Me._TcpClient.GetStream().DataAvailable) Then
                Dim stream As NetworkStream = Me._TcpClient.GetStream()
                Dim frameCount = 2
                Dim bytes As Byte()
                Dim data As String
                ReDim bytes(Me._TcpClient.Client.Available)
                stream.Read(bytes, 0, bytes.Length) 'Read the stream, don't close it.. 

                    Dim length As UInteger = bytes(1) - 128 'this should obviously be a byte (unsigned 8bit value)

                    If length > -1 Then
                        If length = 126 Then
                            length = 4
                        ElseIf length = 127 Then
                            length = 10
                        End If
                    End If

                    'the following is very inefficient and likely unnecessary.. 
                    'the main purpose is to just get the lower 4 bits of byte(0) - which is the OPCODE

                    Dim value As Integer = bytes(0)
                    Dim bitArray As BitArray = New BitArray(8)

                    For c As Integer = 0 To 7 Step 1
                        If value - (2 ^ (7 - c)) >= 0 Then
                            bitArray.Item(c) = True
                            value -= (2 ^ (7 - c))
                            bitArray.Item(c) = False
                        End If

                    Dim FRRR_OPCODE As String = ""

                    For Each bit As Boolean In bitArray
                        If bit Then
                            FRRR_OPCODE &= "1"
                            FRRR_OPCODE &= "0"
                        End If

                    Dim FIN As Integer = FRRR_OPCODE.Substring(0, 1)
                    Dim RSV1 As Integer = FRRR_OPCODE.Substring(1, 1)
                    Dim RSV2 As Integer = FRRR_OPCODE.Substring(2, 1)
                    Dim RSV3 As Integer = FRRR_OPCODE.Substring(3, 1)
                    Dim opCode As Integer = Convert.ToInt32(FRRR_OPCODE.Substring(4, 4), 2)

                    Dim decoded(bytes.Length - (frameCount + 4)) As Byte
                    Dim key As Byte() = {bytes(frameCount), bytes(frameCount+1), bytes(frameCount+2), bytes(frameCount+3)}

                    Dim j As Integer = 0
                    For i As Integer = (frameCount + 4) To (bytes.Length - 2) Step 1
                        decoded(j) = Convert.ToByte((bytes(i) Xor masks(j Mod 4)))
                        j += 1

                    Select Case opCode
                        Case Is = 1
                            'Text Data Sent From Client

                            data = System.Text.Encoding.UTF8.GetString(decoded)
                            'handle this data

                            Dim Payload As Byte() = System.Text.Encoding.UTF8.GetBytes("Text Recieved")
                            Dim FRRROPCODE As Byte() = Convert.ToByte("10000001", 2) 'FIN is set, and OPCODE is 1 or Text
                            Dim header as byte() = {FRRROPCODE, Convert.ToByte(Payload.Length)}

                            Dim ResponseData As Byte()
                            ReDim ResponseData((header.length + Payload.Length) - 1) 
                            'NOTEWORTHY: if you Redim ResponseData(header.length + Payload.Length).. you'll add a 0 value byte at the end of the response data.. 
                            'which tells the client that your next stream write will be a continuation frame..

                            Dim index as integer = 0

                            Buffer.BlockCopy(header, 0, ResponseData, index, header.length)
                            index += header.length

                            Buffer.BlockCopy(payload, 0, ResponseData, index, payload.length)
                            index += payload.length
                            stream.Write(ResponseData, 0, ResponseData.Length) 
                      Case Is = 2 
                            '// Binary Data Sent From Client 
                            data = System.Text.Encoding.UTF8.GetString(decoded) 
                            Dim response As Byte() = System.Text.Encoding.UTF8.GetBytes("Binary Recieved") 
                             stream.Write(response, 0, response.Length) 
                      Case Is = 9 '// Ping Sent From Client 
                      Case Is = 10 '// Pong Sent From Client 
                      Case Else '// Improper opCode.. disconnect the client 
                            RaiseEvent onClientDisconnect() 
                      End Select 
                Catch ex As Exception 
                    RaiseEvent onClientDisconnect() 
                End Try 
            End If 
        End Sub 
    End Class

    Public Class Server
        Inherits System.Net.Sockets.TcpListener

        Delegate Sub OnClientConnectDelegate(ByVal sender As Object, ByRef Client As WebSocket.Client)
        Event OnClientConnect As OnClientConnectDelegate

        Dim WithEvents PendingCheckTimer As Timers.Timer = New Timers.Timer(500)
        Dim WithEvents ClientDataAvailableTimer As Timers.Timer = New Timers.Timer(50)
        Property ClientCollection As List(Of WebSocket.Client) = New List(Of WebSocket.Client)

        Sub New(ByVal url As String, ByVal port As Integer)
            MyBase.New(IPAddress.Parse(url), port)
        End Sub

        Sub startServer()
        End Sub

        Sub Client_Connected(ByVal sender As Object, ByRef client As WebSocket.Client) Handles Me.OnClientConnect
            AddHandler client.onClientDisconnect, AddressOf Client_Disconnected
        End Sub

        Sub Client_Disconnected()

        End Sub

        Function isClientDisconnected(ByVal client As WebSocket.Client) As Boolean
            isClientDisconnected = False
            If Not client.isConnected Then
                Return True
            End If
        End Function

        Function isClientConnected(ByVal client As WebSocket.Client) As Boolean
            isClientConnected = False
            If client.isConnected Then
                Return True
            End If
        End Function

        Private Sub PendingCheckTimer_Elapsed(ByVal sender As Object, ByVal e As System.Timers.ElapsedEventArgs) Handles PendingCheckTimer.Elapsed
            If Pending() Then
                RaiseEvent OnClientConnect(Me, New CORE.TypeDef.WebSocket.Client(Me.AcceptTcpClient()))
            End If
        End Sub

        Private Sub ClientDataAvailableTimer_Elapsed(ByVal sender As Object, ByVal e As System.Timers.ElapsedEventArgs) Handles ClientDataAvailableTimer.Elapsed
            Me.ClientCollection.RemoveAll(AddressOf isClientDisconnected)
            If Me.ClientCollection.Count < 1 Then ClientDataAvailableTimer.Stop()

            For Each Client As WebSocket.Client In Me.ClientCollection
        End Sub
    End Class
End Namespace

Sub Main()  'Program Entry point
    Dim thread As System.Threading.Thread = New System.Threading.Thread(AddressOf StartWebSocketServer)
    'Application.Add("WebSocketServerThread", thread) 'Global.asax - context.Application .. I left this part in for web application developers  
End Sub

Public Shared WebSocketServer As TypeDef.WebSocket.Server
Public Shared Sub StartWebSocketServer()
    WebSocketServer = New TypeDef.WebSocket.Server("", 8000)
End Sub

Document Tags and Contributors

 Contributors to this page: luizj, teoli, mrbrc
 Last updated by: luizj,