(VB.NET) Send and Receive WebSocket Messages

This example how to send and receive websocket messages.

A WebSocket message can be composed of one or more frames. The simple case is where a single frame is both the first and last frame in a message. This is the case where the 1st frame in the message has the "final frame" bit set.

This example demonstrates sending and receiving multi-frame messages.

Note: The websockets.chilkat.io server imposes the following limitations:
Messages must be 16K or less, and each connection is limited to a max of 16 echoed messages.

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' This example requires the Chilkat API to have been previously unlocked.
' See Global Unlock Sample for sample code.

Dim ws As New Chilkat.WebSocket

' For brevity, this example does not check for errors when etablishing the WebSocket connection.
' See Establish WebSocket Connection for more complete sample code for making the connection.

Dim rest As New Chilkat.Rest
' Connect to websockets.chilkat.io
' IMPORTANT: websockets.chilkat.io accepts frames of up to 16K in size and echoes them back.
' IMPORTANT: The websockets.chilkat.io server imposes the following limitations: 
' ---------- Messages must be 16K or less, and each connection is limited to a max of 16 echoed messages.
Dim success As Boolean = rest.Connect("websockets.chilkat.io",80,False,False)
ws.UseConnection(rest)
ws.AddClientHeaders()
Dim responseBodyIgnored As String = rest.FullRequestNoBody("GET","/wsChilkatEcho.ashx")
success = ws.ValidateServerHandshake()
If (success <> True) Then
    Debug.WriteLine(ws.LastErrorText)
    Exit Sub
End If


' This example demonstrates sending and receiving a multi-frame message.

' The websocket message will be composed of three text lines, each frame will contain a single line.

' Send the 1st frame in the message.
Dim finalFrame As Boolean = False
success = ws.SendFrame("This is the 1st frame" & vbCrLf,finalFrame)
If (success <> True) Then
    Debug.WriteLine(ws.LastErrorText)
    Exit Sub
End If


' Send the 2nd frame in the message.
success = ws.SendFrame("This is the 2nd frame" & vbCrLf,finalFrame)
If (success <> True) Then
    Debug.WriteLine(ws.LastErrorText)
    Exit Sub
End If


' Send the 3rd and final frame in the message.
finalFrame = True
success = ws.SendFrame("This is the 3rd frame" & vbCrLf,finalFrame)
If (success <> True) Then
    Debug.WriteLine(ws.LastErrorText)
    Exit Sub
End If



' Read an incoming frames until we receive the final frame.
' Note: It may be that the echo server (websockets.chilkat.io) responds with 
' the full message in a single final frame.
Dim receivedFinalFrame As Boolean = False
While receivedFinalFrame = False

    success = ws.ReadFrame()
    If (success <> True) Then
        Debug.WriteLine("Failed to receive a frame")
        Debug.WriteLine("ReadFrame fail reason = " & ws.ReadFrameFailReason)
        Debug.WriteLine(ws.LastErrorText)
        Exit Sub
    End If


    receivedFinalFrame = ws.FinalFrame

    ' Show the opcode and final frame bit for the frame just received:
    Debug.WriteLine("Frame opcode: " & ws.FrameOpcode)
    Debug.WriteLine("Final frame: " & receivedFinalFrame)
End While

' Return the message accumulated in the above calls to ReadFrame.
Dim receivedMsg As String = ws.GetFrameData()
Debug.WriteLine("Received: " & receivedMsg)


' Close the websocket connection.
success = ws.SendClose(True,1000,"Closing this websocket.")
If (success <> True) Then
    Debug.WriteLine(ws.LastErrorText)
    Exit Sub
End If


' Read the Close response.
success = ws.ReadFrame()
If (success <> True) Then
    Debug.WriteLine("ReadFrame fail reason = " & ws.ReadFrameFailReason)
    Debug.WriteLine(ws.LastErrorText)
    Exit Sub
End If


' Should receive the "Close" opcode.
Debug.WriteLine("Received opcode: " & ws.FrameOpcode)
' Should be the same status code we sent (1000)
Debug.WriteLine("Received close status code: " & ws.CloseStatusCode)
' The server may echo the close reason.  If not, this will be empty.
Debug.WriteLine("Echoed close reason: " & ws.CloseReason)

Debug.WriteLine("Success.")