Visual FoxPro

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.

Visual FoxPro

LOCAL lnSuccess
LOCAL loWs
LOCAL loRest
LOCAL lcResponseBodyIgnored
LOCAL lnFinalFrame
LOCAL lnReceivedFinalFrame
LOCAL lcReceivedMsg

lnSuccess = 0

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

loWs = CreateObject('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.

loRest = CreateObject('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.
lnSuccess = loRest.Connect("websockets.chilkat.io",80,0,0)
loWs.UseConnection(loRest)
loWs.AddClientHeaders()
lcResponseBodyIgnored = loRest.FullRequestNoBody("GET","/wsChilkatEcho.ashx")
lnSuccess = loWs.ValidateServerHandshake()
IF (lnSuccess <> 1) THEN
    ? loWs.LastErrorText
    RELEASE loWs
    RELEASE loRest
    CANCEL
ENDIF

* 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.
lnFinalFrame = 0
lnSuccess = loWs.SendFrame("This is the 1st frame" + CHR(13) + CHR(10),lnFinalFrame)
IF (lnSuccess <> 1) THEN
    ? loWs.LastErrorText
    RELEASE loWs
    RELEASE loRest
    CANCEL
ENDIF

* Send the 2nd frame in the message.
lnSuccess = loWs.SendFrame("This is the 2nd frame" + CHR(13) + CHR(10),lnFinalFrame)
IF (lnSuccess <> 1) THEN
    ? loWs.LastErrorText
    RELEASE loWs
    RELEASE loRest
    CANCEL
ENDIF

* Send the 3rd and final frame in the message.
lnFinalFrame = 1
lnSuccess = loWs.SendFrame("This is the 3rd frame" + CHR(13) + CHR(10),lnFinalFrame)
IF (lnSuccess <> 1) THEN
    ? loWs.LastErrorText
    RELEASE loWs
    RELEASE loRest
    CANCEL
ENDIF

* 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.
lnReceivedFinalFrame = 0
DO WHILE lnReceivedFinalFrame = 0

    lnSuccess = loWs.ReadFrame()
    IF (lnSuccess <> 1) THEN
        ? "Failed to receive a frame"
        ? "ReadFrame fail reason = " + STR(loWs.ReadFrameFailReason)
        ? loWs.LastErrorText
        RELEASE loWs
        RELEASE loRest
        CANCEL
    ENDIF

    lnReceivedFinalFrame = loWs.FinalFrame

    * Show the opcode and final frame bit for the frame just received:
    ? "Frame opcode: " + loWs.FrameOpcode
    ? "Final frame: " + STR(lnReceivedFinalFrame)
ENDDO

* Return the message accumulated in the above calls to ReadFrame.
lcReceivedMsg = loWs.GetFrameData()
? "Received: " + lcReceivedMsg

* Close the websocket connection.
lnSuccess = loWs.SendClose(1,1000,"Closing this websocket.")
IF (lnSuccess <> 1) THEN
    ? loWs.LastErrorText
    RELEASE loWs
    RELEASE loRest
    CANCEL
ENDIF

* Read the Close response.
lnSuccess = loWs.ReadFrame()
IF (lnSuccess <> 1) THEN
    ? "ReadFrame fail reason = " + STR(loWs.ReadFrameFailReason)
    ? loWs.LastErrorText
    RELEASE loWs
    RELEASE loRest
    CANCEL
ENDIF

* Should receive the "Close" opcode.
? "Received opcode: " + loWs.FrameOpcode
* Should be the same status code we sent (1000)
? "Received close status code: " + STR(loWs.CloseStatusCode)
* The server may echo the close reason.  If not, this will be empty.
? "Echoed close reason: " + loWs.CloseReason

? "Success."

RELEASE loWs
RELEASE loRest