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Tcl Examples

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(Tcl) WebSocket Send/Receive Binary Data

Demonstrates how to send and receive binary data on a websocket. This example uses Chilkat's websocket test echo server at ws://websockets.chilkat.io/wsChilkatEcho.ashx

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.

Chilkat Tcl Extension Downloads

Chilkat Tcl Extension Downloads

load ./chilkat.dll

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

set ws [new_CkWebSocket]

# 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.

set rest [new_CkRest]

# 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.
set success [CkRest_Connect $rest "websockets.chilkat.io" 80 0 0]
CkWebSocket_UseConnection $ws $rest
CkWebSocket_AddClientHeaders $ws
set responseBodyIgnored [CkRest_fullRequestNoBody $rest "GET" "/wsChilkatEcho.ashx"]
set success [CkWebSocket_ValidateServerHandshake $ws]
if {[expr $success != 1]} then {
    puts [CkWebSocket_lastErrorText $ws]
    delete_CkWebSocket $ws
    delete_CkRest $rest
    exit
}

# This example sends a small JPG file (about 7KB) in a websocket frame.
set jpgData [new_CkBinData]

set success [CkBinData_LoadFile $jpgData "qa_data/jpg/starfish.jpg"]

puts "Number of bytes to send = [CkBinData_get_NumBytes $jpgData]"

# Send a frame containing the JPG image data.
# This will be the first and final frame, and therefore this constitutes the entire message.
set finalFrame 1
set success [CkWebSocket_SendFrameBd $ws $jpgData $finalFrame]
if {[expr $success != 1]} then {
    puts [CkWebSocket_lastErrorText $ws]
    delete_CkWebSocket $ws
    delete_CkRest $rest
    delete_CkBinData $jpgData
    exit
}

# Read the echoed binary frame(s).
# (We sent the JPG file in a single frame, but we may receive the echo in multiple frames, but it will be one message.)
# Read an incoming frames until we receive the final frame.
set receivedFinalFrame 0
while {[expr $receivedFinalFrame == 0]} {

    # The ws object is accumulating the received data internally.  Once we get the final frame, we'll get the 
    # accumulated data which should constitute the entire JPG.
    set success [CkWebSocket_ReadFrame $ws]
    if {[expr $success != 1]} then {
        puts "Failed to receive a frame"
        puts "ReadFrame fail reason = [CkWebSocket_get_ReadFrameFailReason $ws]"
        puts [CkWebSocket_lastErrorText $ws]
        delete_CkWebSocket $ws
        delete_CkRest $rest
        delete_CkBinData $jpgData
        exit
    }

    set receivedFinalFrame [CkWebSocket_get_FinalFrame $ws]

    # Show the opcode and final frame bit for the frame just received:
    puts "Frame opcode: [CkWebSocket_frameOpcode $ws]"
    puts "Final frame: $receivedFinalFrame"
}

# Get the accumulated received data.
set jpgReceivedData [new_CkBinData]

CkWebSocket_GetFrameDataBd $ws $jpgReceivedData
puts "Received [CkBinData_get_NumBytes $jpgReceivedData] bytes"

# Save the received JPG to a file so we can check it..
CkBinData_WriteFile $jpgReceivedData "qa_output/starfish_ws.jpg"

# Close the websocket connection.
set success [CkWebSocket_SendClose $ws 1 1000 "Closing this websocket."]
if {[expr $success != 1]} then {
    puts [CkWebSocket_lastErrorText $ws]
    delete_CkWebSocket $ws
    delete_CkRest $rest
    delete_CkBinData $jpgData
    delete_CkBinData $jpgReceivedData
    exit
}

# Read the Close response.
set success [CkWebSocket_ReadFrame $ws]
if {[expr $success != 1]} then {
    puts "ReadFrame fail reason = [CkWebSocket_get_ReadFrameFailReason $ws]"
    puts [CkWebSocket_lastErrorText $ws]
    delete_CkWebSocket $ws
    delete_CkRest $rest
    delete_CkBinData $jpgData
    delete_CkBinData $jpgReceivedData
    exit
}

# Should receive the "Close" opcode.
puts "Received opcode: [CkWebSocket_frameOpcode $ws]"
# Should be the same status code we sent (1000)
puts "Received close status code: [CkWebSocket_get_CloseStatusCode $ws]"
# The server may echo the close reason.  If not, this will be empty.
puts "Echoed close reason: [CkWebSocket_closeReason $ws]"

puts "Success."

delete_CkWebSocket $ws
delete_CkRest $rest
delete_CkBinData $jpgData
delete_CkBinData $jpgReceivedData

 

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