WebSocket Dart Reference Documentation
CkWebSocket
Current Version: 11.6.1
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 true, then retrieve the accumulated data with
GetFrameData, GetFrameDataSb, or
GetFrameDataBd.
Object Creation
// pubspec.yaml:
// dependencies:
// chilkat: ^11.6.1
import 'package:chilkat/chilkat.dart';
// Once per process, before any other Chilkat call:
Chilkat.unlockBundle('Anything for 30-day trial'); // shorthand for CkGlobal().unlockBundle(..)
final webSocket = CkWebSocket();
// ... the native object is released when `webSocket` is garbage collected, or now with webSocket.dispose().Creates the underlying native Chilkat object. Use a CkWebSocket only from the isolate that created it: Chilkat objects cannot be sent between isolates. Every call is synchronous; in a Flutter app, run long operations (network, large files) inside Isolate.run, creating the Chilkat objects inside the isolate.
Releases the native object immediately instead of waiting for garbage collection (useful for a large CkBinData or an open socket). Calling it more than once is harmless; any other use of the object afterwards throws a StateError. isDisposed tells whether it has been called.
Errors
A method that can fail throws a ChilkatException: a method whose only outcome is success or failure returns void and throws on failure; a method producing a String or an object returns it and throws where Chilkat would have returned null. The exception carries the object's LastErrorText at the time of the failure (lastErrorText), the class and method names (className, methodName) and a one-line message. Properties never throw, and methods that answer a question (has..., is..., ...) return a plain bool.
try {
webSocket.someMethod(...);
} on ChilkatException catch (e) {
print(e); // CkWebSocket.someMethod failed: <reason>
print(e.lastErrorText); // the full Chilkat log of the failed call
}
Properties
CloseAutoRespond
bool get closeAutoRespond
set closeAutoRespond(bool value)
Controls whether Chilkat automatically answers an incoming Close control frame.
- When
true, 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
false, the application can detect the received Close throughCloseReceivedorFrameOpcodeand callSendCloseitself.
The default is true.
CloseReason
String get closeReason
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
bool get closeReceived
true after a Close control frame has been received on the current WebSocket connection.
When CloseAutoRespond is false, 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
int get closeStatusCode
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
String get debugLogFilePath
set debugLogFilePath(String value)
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
bool get finalFrame
true if the frame most recently delivered by ReadFrame had its WebSocket FIN bit set; otherwise false.
For a fragmented data message, continue reading while this property is false. The fragment with true completes the message. Unfragmented messages have true on their only frame.
FIN bit is always set.
FrameDataLen
int get frameDataLen
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
String get frameOpcode
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
int get frameOpcodeInt
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.
HeartbeatMs
int get heartbeatMs
set heartbeatMs(int value)
Specifies the interval, in milliseconds, between AbortCheck event callbacks during supported blocking operations.
The default is 0, which disables periodic AbortCheck callbacks. Set a positive value when the application needs an opportunity to cancel a long-running send or receive operation.
SendPing and Ping/Pong handling for protocol-level heartbeat behavior.
IdleTimeoutMs
int get idleTimeoutMs
set idleTimeoutMs(int value)
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
bool get isConnected
true when the underlying WebSocket network connection is currently open; otherwise false.
LastErrorHtml
String get lastErrorHtml
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
String get lastErrorText
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
String get lastErrorXml
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
bool get lastMethodSuccess
set lastMethodSuccess(bool value)
Indicates the success or failure of the most recent method call: true means success, false 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
bool get needSendPong
true when a Ping frame has been received but no corresponding Pong has yet been sent.
This property is primarily useful when PingAutoRespond is false. Call SendPong as soon as practical; it automatically sends the received Ping payload in the Pong response.
PingAutoRespond
bool get pingAutoRespond
set pingAutoRespond(bool value)
Controls automatic handling of incoming Ping control frames.
- When
true, Chilkat sends the required Pong automatically andReadFrameconsumes the Ping internally, continuing until another frame is available. - When
false, the Ping can be returned to the application. CheckNeedSendPongand callSendPongas soon as practical.
The default is true.
SendPong automatically uses the stored payload of the unanswered Ping.
PongAutoConsume
bool get pongAutoConsume
set pongAutoConsume(bool value)
Controls whether incoming Pong control frames are hidden from the application.
- When
true,ReadFrameconsumes Pong frames internally and continues reading until a non-Pong frame is available. - When
false, an incoming Pong can be returned normally withFrameOpcodeequal toPong.
The default is true. Check PongConsumed after ReadFrame to learn whether one or more Pong frames were consumed during that call.
PongConsumed
bool get pongConsumed
true if the most recent call to ReadFrame internally consumed a Pong frame while PongAutoConsume was true.
The property is reset to false at the beginning of each ReadFrame call and set to true if a Pong is consumed during that call.
ReadFrameFailReason
int get readFrameFailReason
When ReadFrame returns false, 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
String get uncommonOptions
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. |
VerboseLogging
bool get verboseLogging
set verboseLogging(bool value)
If set to true, then the contents of LastErrorText (or LastErrorXml, or LastErrorHtml) may contain more verbose information. The default value is false. Verbose logging should only be used for debugging. The potentially large quantity of logged information may adversely affect peformance.
Version
String get version
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 normally on success; throws a ChilkatException on 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 normally on success; throws a ChilkatException on failure.
GetFrameData
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 true, and then call GetFrameData once. Calling this method earlier returns and clears only the data accumulated so far.
Throws a ChilkatException on failure (where the description says null is returned, the Dart method throws instead).
GetFrameDataBd
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.
Returns normally on success; throws a ChilkatException on failure.
GetFrameDataSb
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 true before calling this method when the application wants the complete message.
Returns normally on success; throws a ChilkatException on failure.
PollDataAvailable
Checks whether bytes are currently waiting to be read from the underlying WebSocket connection.
Returns true when incoming data is available and false when no data is presently waiting.
true result does not mean that an entire WebSocket frame or message has arrived. Call ReadFrame to parse the protocol frame. A false 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 true, 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 false, inspect ReadFrameFailReason and LastErrorText.
Returns normally on success; throws a ChilkatException on failure.
SendClose
Sends a WebSocket Close control frame and begins or completes the closing handshake.
- If
includeStatusisfalse, the Close frame contains no status code andstatusCodeandreasonare ignored. - If
includeStatusistrue, 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 normally on success; throws a ChilkatException on failure.
SendFrame
Sends one WebSocket text data frame containing stringToSend. WebSocket text data is UTF-8 on the wire.
- Set
finalFrametotruewhen this frame completes the message. - Set
finalFrametofalsewhen 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 true. For a fragmented message, call it repeatedly and set true only for the final fragment.
Returns normally on success; throws a ChilkatException on failure.
SendFrameBd
Sends one WebSocket binary data frame containing the current bytes in bdToSend.
- Set
finalFrametotruewhen this frame completes the binary message. - Set
finalFrametofalsewhen additional binary-message fragments will follow.
For an ordinary single-frame binary message, set finalFrame to true.
bdToSend become the frame payload, while Chilkat applies the client-side WebSocket framing and masking required by the protocol.
Returns normally on success; throws a ChilkatException on failure.
SendFrameSb
Sends one WebSocket text data frame containing the current contents of sbToSend.
- Set
finalFrametotruewhen this frame completes the message. - Set
finalFrametofalsewhen more fragments will follow.
For an ordinary single-frame text message, set finalFrame to true. WebSocket text data is UTF-8 on the wire.
finalFrame set to false create fragments of the same text message. Complete the message with a final call that passes true.
Returns normally on success; throws a ChilkatException on failure.
SendPing
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 normally on success; throws a ChilkatException 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 false and NeedSendPong is true. When automatic Ping handling is enabled, Chilkat sends the Pong internally.
Returns normally on success; throws a ChilkatException on failure.
ShareConnection
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 normally on success; throws a ChilkatException on failure.
UseConnection
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 normally on success; throws a ChilkatException on 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 true, 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 normally on success; throws a ChilkatException on failure.
Events
All Chilkat methods are synchronous: the call returns when the work is done. During a call, CkWebSocket raises three events so your application can show progress and offer a way out. Each event is a nullable callback property on the object; assign a function to receive it, or null to stop receiving it:
final webSocket = CkWebSocket();
webSocket.onPercentDone = (pct) {
print('$pct%');
return false; // return true to abort the method in progress
};
webSocket.onProgressInfo = (name, value) => print('$name: $value');
webSocket.heartbeatMs = 250; // raise onAbortCheck 4 times per second during Chilkat calls
webSocket.onAbortCheck = () => _userPressedCancel;AbortCheck fires at regular intervals controlled by the HeartbeatMs property (0, the default, disables it); PercentDone fires when an operation's completion percentage is known; ProgressInfo delivers named progress values. Returning true from onAbortCheck or onPercentDone aborts the running method, which then throws a ChilkatException.
Events fire on the thread that called the method, before that method returns. An exception thrown inside a callback aborts the running method and is rethrown from it once the native library has returned. In a Flutter app the callbacks run inside the worker isolate that owns the object; forward progress to the UI through a SendPort, and let onAbortCheck read a flag the UI sets the same way.
AbortCheck
bool Function()? onAbortCheck
Enables a method call to be aborted by triggering the AbortCheck event at intervals defined by the HeartbeatMs property. If HeartbeatMs is set to its default value of 0, no events will occur. For instance, set HeartbeatMs to 200 to trigger 5 AbortCheck events per second.
Example:
webSocket.heartbeatMs = 250; // call onAbortCheck 4 times per second
var cancelRequested = false;
webSocket.onAbortCheck = () => cancelRequested;
// ... set cancelRequested = true (e.g. from a message received on a ReceivePort) to abort the method in progressPercentDone
bool Function(int pctDone)? onPercentDone
This provides the percentage completion for any method involving network communications or time-consuming processing, assuming the progress can be measured as a percentage. This event is triggered only when it's possible and logical to express the operation's progress as a percentage. The pctDone argument will range from 1 to 100. For methods that finish quickly, the number of PercentDone callbacks may vary, but the final callback will have pctDone equal to 100. For longer operations, callbacks will not exceed one per percentage point (e.g., 1, 2, 3, ..., 98, 99, 100).
The PercentDone callback also acts as an AbortCheck event. For fast methods where PercentDone fires, an AbortCheck event may not trigger since the PercentDone callback already provides an opportunity to abort. For longer operations, where time between PercentDone callbacks is extended, AbortCheck callbacks enable more responsive operation termination.
To abort the operation, set the abort output argument to true. This will cause the method to terminate and return a failure status or corresponding failure value.
Example:
webSocket.onPercentDone = (pct) {
// pct ranges from 1 to 100.
print('Percent done: $pct');
return false; // return true to abort the method in progress
};ProgressInfo
void Function(String name, String value)? onProgressInfo
This event callback provides tag name/value pairs that detail what occurs during a method call. To discover existing tag names, create code to handle the event, emit the pairs, and review them. Most tag names are self-explanatory.
Note: Some Chilkat methods don't fire any ProgressInfo events.
Example:
webSocket.onProgressInfo = (name, value) => print('$name: $value');