Tcl

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.

Tcl

load ./chilkat.dll

set success 0

# 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 $ws]
if {$success != 1} then {
    puts [CkWebSocket_lastErrorText $ws]
    delete_CkWebSocket $ws
    delete_CkRest $rest
    exit
}

# 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.
set finalFrame 0
set success [CkWebSocket_SendFrame $ws "This is the 1st frame\r\n" $finalFrame]
if {$success != 1} then {
    puts [CkWebSocket_lastErrorText $ws]
    delete_CkWebSocket $ws
    delete_CkRest $rest
    exit
}

# Send the 2nd frame in the message.
set success [CkWebSocket_SendFrame $ws "This is the 2nd frame\r\n" $finalFrame]
if {$success != 1} then {
    puts [CkWebSocket_lastErrorText $ws]
    delete_CkWebSocket $ws
    delete_CkRest $rest
    exit
}

# Send the 3rd and final frame in the message.
set finalFrame 1
set success [CkWebSocket_SendFrame $ws "This is the 3rd frame\r\n" $finalFrame]
if {$success != 1} then {
    puts [CkWebSocket_lastErrorText $ws]
    delete_CkWebSocket $ws
    delete_CkRest $rest
    exit
}

# 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.
set receivedFinalFrame 0
while {$receivedFinalFrame == 0} {

    set success [CkWebSocket_ReadFrame $ws]
    if {$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
        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"
}

# Return the message accumulated in the above calls to ReadFrame.
set receivedMsg [CkWebSocket_getFrameData $ws]
puts "Received: $receivedMsg"

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

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