B4X

Send and Receive WebSocket Messages

See more WebSocket Examples

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.

B4X

Dim success As Boolean = False

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

Dim ws As ChilkatWebSocket
ws.Initialize("ws")

'  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 ChilkatRest
rest.Initialize("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.
success = 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
    Log(ws.LastErrorText)
    Return
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" & Chr(13) & Chr(10), finalFrame)
If success <> True Then
    Log(ws.LastErrorText)
    Return
End If


'  Send the 2nd frame in the message.
success = ws.SendFrame("This is the 2nd frame" & Chr(13) & Chr(10), finalFrame)
If success <> True Then
    Log(ws.LastErrorText)
    Return
End If


'  Send the 3rd and final frame in the message.
finalFrame = True
success = ws.SendFrame("This is the 3rd frame" & Chr(13) & Chr(10), finalFrame)
If success <> True Then
    Log(ws.LastErrorText)
    Return
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
Do While receivedFinalFrame = False

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


    receivedFinalFrame = ws.FinalFrame

    '  Show the opcode and final frame bit for the frame just received:
    Log("Frame opcode: " & ws.FrameOpcode)
    Log("Final frame: " & receivedFinalFrame)
Loop

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

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


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


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

Log("Success.")