WebSocket Tcl Reference Documentation
WebSocket
Current Version: 11.5.0
Chilkat.WebSocket
Upgrade a connected
Send UTF-8 text or exact binary bytes as single-frame or fragmented
WebSocket messages.
Read frames, inspect opcodes and the FIN state, and accumulate fragments
until a complete message is available.
Use automatic or manual control-frame handling for keep-alive and
responsiveness checks.
Exchange Close frames, inspect the peer's status code and reason, and
terminate the underlying connection cleanly.
Share a connection between two WebSocket objects when one thread needs
to read while another writes.
For an extended overview, see
WebSocket Class Overview.
Connect to WebSocket servers and exchange client-side frames and messages.
Chilkat.WebSocket implements the client side of the WebSocket
protocol. It initiates an opening handshake with an existing WebSocket
server. It does not listen for incoming connections, accept clients, or
implement a WebSocket server.
Chilkat.WebSocket operates over an established
Chilkat.Rest connection. It creates and validates the HTTP
upgrade handshake, sends and receives text or binary frames, supports
fragmented messages, handles Ping, Pong, and Close control frames, polls for
incoming data, and exposes frame-level diagnostics.
Client opening handshake
Rest session to WebSocket and validate
the server's response before exchanging frames.
Text and binary messages
Frame-by-frame receiving
Ping and Pong
Clean close handshake
Separate read/write paths
Rest object to the server, call
UseConnection, call AddClientHeaders, send the
opening HTTP GET request through Rest, and then
call ValidateServerHandshake. Only after validation succeeds
should the application call frame send/receive methods.
ReadFrame until
FinalFrame is 1, then retrieve the accumulated data with
GetFrameData, GetFrameDataSb, or
GetFrameDataBd.
Object Creation
# 'this' is not a keyword in Tcl. It can freely be used as a variable name. set this [new CkWebSocket]
Properties
CloseAutoRespond
set boolVal [CkWebSocket_get_CloseAutoRespond $this]
CkWebSocket_put_CloseAutoRespond $this $boolVal
Controls whether Chilkat automatically answers an incoming Close control frame.
- When
1, an incoming Close is answered automatically if the client did not already initiate the close. After a Close has been both received and sent, Chilkat closes the underlying connection. - When
0, the application can detect the received Close throughCloseReceivedorFrameOpcodeand callSendCloseitself.
The default is 1.
CloseReason
# ckStr is a CkString
CkWebSocket_get_CloseReason $this $ckStr
set strVal [CkWebSocket_get_closeReason $this]
Returns the UTF-8 reason text contained in the received Close control frame.
The value is empty when the peer supplied no reason or when no Close frame has been received. A reason is diagnostic text and should not be treated as a stable machine-readable error identifier; use CloseStatusCode for protocol-level handling.
CloseReceived
set boolVal [CkWebSocket_get_CloseReceived $this]
1 after a Close control frame has been received on the current WebSocket connection.
When CloseAutoRespond is 0, use this property to determine whether the application needs to call SendClose to complete the closing handshake. The received status code and reason, if present, are available through CloseStatusCode and CloseReason.
CloseStatusCode
set intVal [CkWebSocket_get_CloseStatusCode $this]
Returns the status code contained in the received Close control frame.
Returns 0 when no Close frame has been received or when the received Close frame did not include a status code.
0 is an API sentinel; it is not a WebSocket close status transmitted by the peer.
DebugLogFilePath
# ckStr is a CkString
CkWebSocket_get_DebugLogFilePath $this $ckStr
set strVal [CkWebSocket_get_debugLogFilePath $this]
CkWebSocket_put_DebugLogFilePath $this $strVal
If set to a file path, this property logs the LastErrorText of each Chilkat method or property call to the specified file. This logging helps identify the context and history of Chilkat calls leading up to any crash or hang, aiding in debugging.
Enabling the VerboseLogging property provides more detailed information. This property is mainly used for debugging rare instances where a Chilkat method call causes a hang or crash, which should generally not happen.
Possible causes of hangs include:
- A timeout property set to 0, indicating an infinite timeout.
- A hang occurring within an event callback in the application code.
- An internal bug in the Chilkat code causing the hang.
FinalFrame
set boolVal [CkWebSocket_get_FinalFrame $this]
1 if the frame most recently delivered by ReadFrame had its WebSocket FIN bit set; otherwise 0.
For a fragmented data message, continue reading while this property is 0. The fragment with 1 completes the message. Unfragmented messages have 1 on their only frame.
FIN bit is always set.
FrameDataLen
set intVal [CkWebSocket_get_FrameDataLen $this]
Returns the number of payload bytes currently accumulated in the internal receive buffer.
The value can represent data from one frame or from multiple calls to ReadFrame, which is useful when receiving a fragmented message. The accumulated bytes remain available until retrieved by GetFrameData, GetFrameDataSb, or GetFrameDataBd.
FinalFrame to determine whether the last received fragment completed the message.
FrameOpcode
# ckStr is a CkString
CkWebSocket_get_FrameOpcode $this $ckStr
set strVal [CkWebSocket_get_frameOpcode $this]
Returns the symbolic opcode of the frame most recently delivered by ReadFrame.
| Value | Meaning |
|---|---|
Continuation | A later fragment of a Text or Binary message |
Text | UTF-8 text data |
Binary | Binary data |
Close | Closing handshake |
Ping | Ping control frame |
Pong | Pong control frame |
Before any frame has been received, the value is the empty string. Ping or Pong frames handled internally by the auto-response/auto-consume options may not be returned as the current frame.
topFrameOpcodeInt
set intVal [CkWebSocket_get_FrameOpcodeInt $this]
Returns the numeric opcode of the frame most recently delivered by ReadFrame.
| Value | Frame type |
|---|---|
0 | Continuation |
1 | Text |
2 | Binary |
8 | Close |
9 | Ping |
10 | Pong |
Use FrameOpcode when a readable symbolic value is preferred.
IdleTimeoutMs
set intVal [CkWebSocket_get_IdleTimeoutMs $this]
CkWebSocket_put_IdleTimeoutMs $this $intVal
Specifies the maximum number of milliseconds an active send or receive operation may remain stalled while waiting for additional network progress.
The default is 30000 milliseconds (30 seconds). This is an inactivity timeout, not a total limit on the duration of the operation. An operation may continue longer than this value as long as data continues to be transferred.
SendPing when the application needs protocol-level keep-alive or responsiveness checks.
IsConnected
set boolVal [CkWebSocket_get_IsConnected $this]
1 when the underlying WebSocket network connection is currently open; otherwise 0.
LastErrorHtml
# ckStr is a CkString
CkWebSocket_get_LastErrorHtml $this $ckStr
set strVal [CkWebSocket_get_lastErrorHtml $this]
Provides HTML-formatted information about the last called method or property. If a method call fails or behaves unexpectedly, check this property for details. Note that information is available regardless of the method call's success.
topLastErrorText
# ckStr is a CkString
CkWebSocket_get_LastErrorText $this $ckStr
set strVal [CkWebSocket_get_lastErrorText $this]
Provides plain text information about the last called method or property. If a method call fails or behaves unexpectedly, check this property for details. Note that information is available regardless of the method call's success.
LastErrorXml
# ckStr is a CkString
CkWebSocket_get_LastErrorXml $this $ckStr
set strVal [CkWebSocket_get_lastErrorXml $this]
Provides XML-formatted information about the last called method or property. If a method call fails or behaves unexpectedly, check this property for details. Note that information is available regardless of the method call's success.
topLastMethodSuccess
set boolVal [CkWebSocket_get_LastMethodSuccess $this]
CkWebSocket_put_LastMethodSuccess $this $boolVal
Indicates the success or failure of the most recent method call: 1 means success, 0 means failure. This property remains unchanged by property setters or getters. This method is present to address challenges in checking for null or Nothing returns in certain programming languages. Note: This property does not apply to methods that return integer values or to boolean-returning methods where the boolean does not indicate success or failure.
NeedSendPong
set boolVal [CkWebSocket_get_NeedSendPong $this]
1 when a Ping frame has been received but no corresponding Pong has yet been sent.
This property is primarily useful when PingAutoRespond is 0. Call SendPong as soon as practical; it automatically sends the received Ping payload in the Pong response.
PingAutoRespond
set boolVal [CkWebSocket_get_PingAutoRespond $this]
CkWebSocket_put_PingAutoRespond $this $boolVal
Controls automatic handling of incoming Ping control frames.
- When
1, Chilkat sends the required Pong automatically andReadFrameconsumes the Ping internally, continuing until another frame is available. - When
0, the Ping can be returned to the application. CheckNeedSendPongand callSendPongas soon as practical.
The default is 1.
SendPong automatically uses the stored payload of the unanswered Ping.
PongAutoConsume
set boolVal [CkWebSocket_get_PongAutoConsume $this]
CkWebSocket_put_PongAutoConsume $this $boolVal
Controls whether incoming Pong control frames are hidden from the application.
- When
1,ReadFrameconsumes Pong frames internally and continues reading until a non-Pong frame is available. - When
0, an incoming Pong can be returned normally withFrameOpcodeequal toPong.
The default is 1. Check PongConsumed after ReadFrame to learn whether one or more Pong frames were consumed during that call.
PongConsumed
set boolVal [CkWebSocket_get_PongConsumed $this]
1 if the most recent call to ReadFrame internally consumed a Pong frame while PongAutoConsume was 1.
The property is reset to 0 at the beginning of each ReadFrame call and set to 1 if a Pong is consumed during that call.
ReadFrameFailReason
set intVal [CkWebSocket_get_ReadFrameFailReason $this]
When ReadFrame returns 0, this property categorizes the reason:
| Value | Meaning |
|---|---|
0 | No failure is recorded |
1 | Read inactivity timeout |
2 | Aborted by an application callback |
3 | Fatal socket error or lost connection |
4 | Invalid WebSocket frame bytes were received |
99 | Unexpected catch-all failure |
Use this value for programmatic branching and inspect LastErrorText for detailed diagnostics.
UncommonOptions
# ckStr is a CkString
CkWebSocket_get_UncommonOptions $this $ckStr
set strVal [CkWebSocket_get_uncommonOptions $this]
Contains a comma-separated list of rarely needed compatibility or platform options. The default is the empty string and should normally remain unchanged.
| Keyword | Effect |
|---|---|
ProtectFromVpn | On Android, attempts to route the connection outside an installed or active VPN. Introduced in v9.5.0.80. |
Utf8
set boolVal [CkWebSocket_get_Utf8 $this]
CkWebSocket_put_Utf8 $this $boolVal
When set to 1, all string arguments and return values are interpreted as UTF-8 strings. When set to 0, they are interpreted as ANSI strings.
In Chilkat v11.0.0 and later, the default value is 1. Before v11.0.0, it was 0.
VerboseLogging
set boolVal [CkWebSocket_get_VerboseLogging $this]
CkWebSocket_put_VerboseLogging $this $boolVal
If set to 1, then the contents of LastErrorText (or LastErrorXml, or LastErrorHtml) may contain more verbose information. The default value is 0. Verbose logging should only be used for debugging. The potentially large quantity of logged information may adversely affect peformance.
Version
# ckStr is a CkString
CkWebSocket_get_Version $this $ckStr
set strVal [CkWebSocket_get_version $this]
Methods
AddClientHeaders
Adds the standard client opening-handshake headers to the Rest object supplied to UseConnection:
Upgrade: websocket Connection: Upgrade Sec-WebSocket-Key: ... Sec-WebSocket-Version: 13
Sec-WebSocket-Key contains a newly generated client nonce used by the server to produce Sec-WebSocket-Accept.
Origin, Authorization, cookies, or Sec-WebSocket-Protocol, add them through the associated Rest object before sending the HTTP upgrade request.
Returns 1 for success, 0 for failure.
CloseConnection
Immediately closes the underlying network connection without completing the WebSocket closing handshake.
Use this method when the connection must be abandoned because of a fatal error, timeout, application shutdown, or an unresponsive peer.
SendClose, receive the peer's Close frame with ReadFrame, and allow the closing handshake to complete. An abrupt transport close does not provide the peer with a WebSocket status code or reason.
Returns 1 for success, 0 for failure.
topGetFrameData
set status [CkWebSocket_GetFrameData $this $outStr]
set retStr [CkWebSocket_getFrameData $this]
Returns the bytes accumulated by successful calls to ReadFrame as a string, then clears the internal receive buffer.
This method is intended for WebSocket text-message data. For arbitrary binary payloads, use GetFrameDataBd to avoid interpreting binary bytes as text.
ReadFrame until FinalFrame is 1, and then call GetFrameData once. Calling this method earlier returns and clears only the data accumulated so far.
Returns 1 for success, 0 for failure.
topGetFrameDataBd
set retBool [CkWebSocket_GetFrameDataBd $this $binData]
Appends the bytes accumulated by successful calls to ReadFrame to binData, then clears the internal receive buffer.
Use this method for binary messages or whenever the exact received bytes must be preserved. Existing data in the destination BinData is retained because the received bytes are appended.
GetFrameData, GetFrameDataSb, or GetFrameDataBd consumes the same internal buffer. Retrieve the data using only the form needed by the application.
GetFrameDataSb
set retBool [CkWebSocket_GetFrameDataSb $this $sb]
Appends the text represented by the bytes accumulated by successful calls to ReadFrame to sb, then clears the internal receive buffer.
Existing text in the destination StringBuilder is retained. This method is most appropriate for text-message data; use GetFrameDataBd for arbitrary binary payloads.
FinalFrame is 1 before calling this method when the application wants the complete message.
LoadTaskCaller
set status [CkWebSocket_LoadTaskCaller $this $task]
Loads the caller object associated with an asynchronous Task method invocation.
This is used by Chilkat's asynchronous task infrastructure when access to the original WebSocket object is required after the task completes.
Returns 1 for success, 0 for failure.
topPollDataAvailable
Checks whether bytes are currently waiting to be read from the underlying WebSocket connection.
Returns 1 when incoming data is available and 0 when no data is presently waiting.
1 result does not mean that an entire WebSocket frame or message has arrived. Call ReadFrame to parse the protocol frame. A 0 result does not indicate that the peer will not send data later.
ReadFrame
Reads the next WebSocket frame from the connected server. On success, the method updates FrameOpcode, FrameOpcodeInt, FinalFrame, and FrameDataLen.
Frame payload bytes are added to an internal receive buffer. The buffer may therefore contain data accumulated by multiple calls to ReadFrame. Retrieve and clear it with GetFrameData, GetFrameDataSb, or GetFrameDataBd.
Call ReadFrame until FinalFrame is 1, then retrieve the accumulated message data. A fragmented message begins with a Text or Binary frame and continues with one or more Continuation frames.
PingAutoRespond and PongAutoConsume, incoming Ping and Pong frames may be handled internally, causing this method to continue reading until another frame is available. If the method returns 0, inspect ReadFrameFailReason and LastErrorText.
Returns 1 for success, 0 for failure.
ReadFrameAsync (1)
set ret_task [CkWebSocket_ReadFrameAsync $this]
Creates an asynchronous task to call the ReadFrame method with the arguments provided.
Returns NULL on failure
SendClose
# statusCode is an integer
# reason is a string
set status [CkWebSocket_SendClose $this $includeStatus $statusCode $reason]
Sends a WebSocket Close control frame and begins or completes the closing handshake.
- If
includeStatusis0, the Close frame contains no status code andstatusCodeandreasonare ignored. - If
includeStatusis1, the frame containsstatusCodefollowed by the UTF-8 bytes ofreason.
The complete Close payload cannot exceed 125 bytes, leaving at most 123 bytes for the UTF-8 reason after the two-byte status code. Chilkat truncates an overlong reason. The API accepts status-code integers from 0 through 16383.
1000 for normal closure, or an appropriate application code in the 3000–4999 range. Codes 1005, 1006, and 1015 are reserved reporting values and must not be sent in a Close frame.
Returns 1 for success, 0 for failure.
topSendCloseAsync (1)
# includeStatus is a boolean
# statusCode is an integer
# reason is a string
set ret_task [CkWebSocket_SendCloseAsync $this $includeStatus $statusCode $reason]
Creates an asynchronous task to call the SendClose method with the arguments provided.
Returns NULL on failure
SendFrame
# finalFrame is a boolean
set status [CkWebSocket_SendFrame $this $stringToSend $finalFrame]
Sends one WebSocket text data frame containing stringToSend. WebSocket text data is UTF-8 on the wire.
- Set
finalFrameto1when this frame completes the message. - Set
finalFrameto0when additional frames will follow as part of the same fragmented message.
For a normal unfragmented text message, call this method once with finalFrame set to 1. For a fragmented message, call it repeatedly and set 1 only for the final fragment.
Returns 1 for success, 0 for failure.
SendFrameAsync (1)
# stringToSend is a string
# finalFrame is a boolean
set ret_task [CkWebSocket_SendFrameAsync $this $stringToSend $finalFrame]
Creates an asynchronous task to call the SendFrame method with the arguments provided.
Returns NULL on failure
SendFrameBd
# finalFrame is a boolean
set status [CkWebSocket_SendFrameBd $this $bdToSend $finalFrame]
Sends one WebSocket binary data frame containing the current bytes in bdToSend.
- Set
finalFrameto1when this frame completes the binary message. - Set
finalFrameto0when additional binary-message fragments will follow.
For an ordinary single-frame binary message, set finalFrame to 1.
bdToSend become the frame payload, while Chilkat applies the client-side WebSocket framing and masking required by the protocol.
Returns 1 for success, 0 for failure.
SendFrameBdAsync (1)
# bdToSend is a CkBinData
# finalFrame is a boolean
set ret_task [CkWebSocket_SendFrameBdAsync $this $bdToSend $finalFrame]
Creates an asynchronous task to call the SendFrameBd method with the arguments provided.
Returns NULL on failure
SendFrameSb
# finalFrame is a boolean
set status [CkWebSocket_SendFrameSb $this $sbToSend $finalFrame]
Sends one WebSocket text data frame containing the current contents of sbToSend.
- Set
finalFrameto1when this frame completes the message. - Set
finalFrameto0when more fragments will follow.
For an ordinary single-frame text message, set finalFrame to 1. WebSocket text data is UTF-8 on the wire.
finalFrame set to 0 create fragments of the same text message. Complete the message with a final call that passes 1.
Returns 1 for success, 0 for failure.
topSendFrameSbAsync (1)
# sbToSend is a CkStringBuilder
# finalFrame is a boolean
set ret_task [CkWebSocket_SendFrameSbAsync $this $sbToSend $finalFrame]
Creates an asynchronous task to call the SendFrameSb method with the arguments provided.
Returns NULL on failure
SendPing
set status [CkWebSocket_SendPing $this $pingData]
Sends a WebSocket Ping control frame. If pingData is non-empty, its UTF-8 bytes are included as the Ping payload.
WebSocket control-frame payloads are limited to 125 bytes. If the UTF-8 representation exceeds this limit, Chilkat truncates it to 125 bytes.
Returns 1 for success, 0 for failure.
SendPingAsync (1)
# pingData is a string
set ret_task [CkWebSocket_SendPingAsync $this $pingData]
Creates an asynchronous task to call the SendPing method with the arguments provided.
Returns NULL on failure
SendPong
Sends a WebSocket Pong control frame.
When a Ping has been received and has not yet been answered, this method automatically uses the previously received Ping payload as the Pong payload, as required for a Ping response.
PingAutoRespond is 0 and NeedSendPong is 1. When automatic Ping handling is enabled, Chilkat sends the Pong internally.
Returns 1 for success, 0 for failure.
topSendPongAsync (1)
set ret_task [CkWebSocket_SendPongAsync $this]
Creates an asynchronous task to call the SendPong method with the arguments provided.
Returns NULL on failure
ShareConnection
set status [CkWebSocket_ShareConnection $this $ws]
Causes the calling WebSocket object to share the already-established WebSocket connection owned by ws.
This enables a bidirectional design in which separate WebSocket objects operate on the same connection—for example, one thread blocks in ReadFrame while another thread sends frames.
Returns 1 for success, 0 for failure.
UseConnection
set status [CkWebSocket_UseConnection $this $connection]
Associates this WebSocket object with an existing, connected Rest object and prepares it for a client-side WebSocket session.
The opening WebSocket handshake is an HTTP GET upgrade request. Using Rest for the underlying connection allows the application to configure TLS, proxies, authentication, custom request headers, IPv6, socket options, bandwidth limits, and other connection features before the upgrade is performed.
- Connect the
Restobject to the server. - Call
UseConnection. - Call
AddClientHeaders. - Send the HTTP
GETrequest with theRestobject. - Call
ValidateServerHandshake.
Returns 1 for success, 0 for failure.
ValidateServerHandshake
Validates the server's response to the WebSocket opening handshake sent through the associated Rest object.
Validation checks that the server accepted the HTTP upgrade and returned the expected WebSocket handshake response, including the value derived from the client's Sec-WebSocket-Key. If this method returns 1, the connection has entered the WebSocket protocol and data or control frames may be exchanged.
Rest object has sent the opening GET request and received the server's response. A successful HTTP request alone does not establish a WebSocket session; the response must also pass this validation.
Returns 1 for success, 0 for failure.