Interface WebSocket

public interface WebSocket

A WebSocket Client.

WebSocket instances are created through WebSocket.Builder.

WebSocket has an input and an output side. These sides are independent from each other. A side can either be open or closed. Once closed, the side remains closed. WebSocket messages are sent through a WebSocket and received through a WebSocket.Listener associated with it. Messages can be sent until the WebSocket's output is closed, and received until the WebSocket's input is closed.

A send method is any of the sendText, sendBinary, sendPing, sendPong and sendClose methods of WebSocket. A send method initiates a send operation and returns a CompletableFuture which completes once the operation has completed. If the CompletableFuture completes normally the operation is considered succeeded. If the CompletableFuture completes exceptionally, the operation is considered failed. An operation that has been initiated but not yet completed is considered pending.

A receive method is any of the onText, onBinary, onPing, onPong and onClose methods of Listener. WebSocket initiates a receive operation by invoking a receive method on the listener. The listener then must return a CompletionStage which completes once the operation has completed.

To control receiving of messages, a WebSocket maintains an internal counter. This counter's value is a number of times the WebSocket has yet to invoke a receive method. While this counter is zero the WebSocket does not invoke receive methods. The counter is incremented by n when request(n) is called. The counter is decremented by one when the WebSocket invokes a receive method. onOpen and onError are not receive methods. WebSocket invokes onOpen prior to any other methods on the listener. WebSocket invokes onOpen at most once. WebSocket may invoke onError at any given time. If the WebSocket invokes onError or onClose, then no further listener's methods will be invoked, no matter the value of the counter. For a newly built WebSocket the counter is zero.

Unless otherwise stated, null arguments will cause methods of WebSocket to throw NullPointerException, similarly, WebSocket will not pass null arguments to methods of Listener. The state of a WebSocket is not changed by the invocations that throw or return a CompletableFuture that completes with one of the NullPointerException, IllegalArgumentException, IllegalStateException exceptions.

WebSocket handles received Ping and Close messages automatically (as per the WebSocket Protocol) by replying with Pong and Close messages. If the listener receives Ping or Close messages, no mandatory actions from the listener are required.

API Note:: The relationship between a WebSocket and the associated Listener is analogous to that of a Subscription and the associated Subscriber of type Flow.
Since:: 11

Nested Class Summary

Nested Classes
Modifier and Type	Interface	Description
`static interface`	`WebSocket.Builder`	A builder of WebSocket Clients.
`static interface`	`WebSocket.Listener`	The receiving interface of `WebSocket`.

Field Summary

Fields
Modifier and Type	Field	Description
`static int`	`NORMAL_CLOSURE`	The WebSocket Close message status code (`1000`), indicating normal closure, meaning that the purpose for which the connection was established has been fulfilled.

Method Summary

All Methods Instance Methods Abstract Methods
Modifier and Type	Method	Description
`void`	`abort()`	Closes this WebSocket's input and output abruptly.
`String`	`getSubprotocol()`	Returns the subprotocol used by this WebSocket.
`boolean`	`isInputClosed()`	Tells whether this WebSocket's input is closed.
`boolean`	`isOutputClosed()`	Tells whether this WebSocket's output is closed.
`void`	`request(long n)`	Increments the counter of invocations of receive methods.
`CompletableFuture<WebSocket>`	`sendBinary(ByteBuffer data, boolean last)`	Sends binary data with bytes from the given buffer.
`CompletableFuture<WebSocket>`	`sendClose(int statusCode, String reason)`	Initiates an orderly closure of this WebSocket's output by sending a Close message with the given status code and the reason.
`CompletableFuture<WebSocket>`	`sendPing(ByteBuffer message)`	Sends a Ping message with bytes from the given buffer.
`CompletableFuture<WebSocket>`	`sendPong(ByteBuffer message)`	Sends a Pong message with bytes from the given buffer.
`CompletableFuture<WebSocket>`	`sendText(CharSequence data, boolean last)`	Sends textual data with characters from the given character sequence.

Field Detail

NORMAL_CLOSURE

static final int NORMAL_CLOSURE

The WebSocket Close message status code (1000), indicating normal closure, meaning that the purpose for which the connection was established has been fulfilled.

See Also:: sendClose(int, String), WebSocket.Listener.onClose(WebSocket, int, String), Constant Field Values

Method Detail

sendText

CompletableFuture<WebSocket> sendText(CharSequence data,
                                      boolean last)

Sends textual data with characters from the given character sequence.

The character sequence must not be modified until the CompletableFuture returned from this method has completed.

A CompletableFuture returned from this method can complete exceptionally with:

IllegalStateException - if there is a pending text or binary send operation or if the previous binary data does not complete the message
IOException - if an I/O error occurs, or if the output is closed

Implementation Note:: If data is a malformed UTF-16 sequence, the operation will fail with IOException.
Parameters:: data - the data; last - true if this invocation completes the message, false otherwise
Returns:: a CompletableFuture that completes, with this WebSocket, when the data has been sent

sendBinary

CompletableFuture<WebSocket> sendBinary(ByteBuffer data,
                                        boolean last)

Sends binary data with bytes from the given buffer.

The data is located in bytes from the buffer's position to its limit. Upon normal completion of a CompletableFuture returned from this method the buffer will have no remaining bytes. The buffer must not be accessed until after that.

The CompletableFuture returned from this method can complete exceptionally with:

IllegalStateException - if there is a pending text or binary send operation or if the previous textual data does not complete the message
IOException - if an I/O error occurs, or if the output is closed

Parameters:: data - the data; last - true if this invocation completes the message, false otherwise
Returns:: a CompletableFuture that completes, with this WebSocket, when the data has been sent

sendPing

CompletableFuture<WebSocket> sendPing(ByteBuffer message)

Sends a Ping message with bytes from the given buffer.

The message consists of not more than 125 bytes from the buffer's position to its limit. Upon normal completion of a CompletableFuture returned from this method the buffer will have no remaining bytes. The buffer must not be accessed until after that.

The CompletableFuture returned from this method can complete exceptionally with:

IllegalStateException - if there is a pending ping or pong send operation
IllegalArgumentException - if the message is too long
IOException - if an I/O error occurs, or if the output is closed

Parameters:: message - the message
Returns:: a CompletableFuture that completes, with this WebSocket, when the Ping message has been sent

sendPong

CompletableFuture<WebSocket> sendPong(ByteBuffer message)

Sends a Pong message with bytes from the given buffer.

Given that the WebSocket implementation will automatically send a reciprocal pong when a ping is received, it is rarely required to send a pong message explicitly.

The CompletableFuture returned from this method can complete exceptionally with:

IllegalStateException - if there is a pending ping or pong send operation
IllegalArgumentException - if the message is too long
IOException - if an I/O error occurs, or if the output is closed

Parameters:: message - the message
Returns:: a CompletableFuture that completes, with this WebSocket, when the Pong message has been sent

sendClose

CompletableFuture<WebSocket> sendClose(int statusCode,
                                       String reason)

Initiates an orderly closure of this WebSocket's output by sending a Close message with the given status code and the reason.

The statusCode is an integer from the range 1000 <= code <= 4999. Status codes 1002, 1003, 1006, 1007, 1009, 1010, 1012, 1013 and 1015 are illegal. Behaviour in respect to other status codes is implementation-specific. A legal reason is a string that has a UTF-8 representation not longer than 123 bytes.

A CompletableFuture returned from this method can complete exceptionally with:

IllegalArgumentException - if statusCode is illegal, or if reason is illegal
IOException - if an I/O error occurs, or if the output is closed

Unless the CompletableFuture returned from this method completes with IllegalArgumentException, or the method throws NullPointerException, the output will be closed.

If not already closed, the input remains open until a Close message received, or abort is invoked, or an error occurs.

API Note:

Use the provided integer constant NORMAL_CLOSURE as a status code and an empty string as a reason in a typical case:

CompletableFuture<WebSocket> webSocket = ...
    webSocket.thenCompose(ws -> ws.sendText("Hello, ", false))
             .thenCompose(ws -> ws.sendText("world!", true))
             .thenCompose(ws -> ws.sendClose(WebSocket.NORMAL_CLOSURE, ""))
             .join();

The sendClose method does not close this WebSocket's input. It merely closes this WebSocket's output by sending a Close message. To enforce closing the input, invoke the abort method. Here is an example of an application that sends a Close message, and then starts a timer. Once no data has been received within the specified timeout, the timer goes off and the alarm aborts WebSocket:

MyAlarm alarm = new MyAlarm(webSocket::abort);
    WebSocket.Listener listener = new WebSocket.Listener() {

        public CompletionStage<?> onText(WebSocket webSocket,
                                         CharSequence data,
                                         boolean last) {
            alarm.snooze();
            ...
        }
        ...
    };
    ...
    Runnable startTimer = () -> {
        MyTimer idleTimer = new MyTimer();
        idleTimer.add(alarm, 30, TimeUnit.SECONDS);
    };
    webSocket.sendClose(WebSocket.NORMAL_CLOSURE, "ok").thenRun(startTimer);

Parameters:

statusCode - the status code

reason - the reason

Returns:

a CompletableFuture that completes, with this WebSocket, when the Close message has been sent

request

void request(long n)

Increments the counter of invocations of receive methods.

This WebSocket will invoke onText, onBinary, onPing, onPong or onClose methods on the associated listener (i.e. receive methods) up to n more times.

API Note:

The parameter of this method is the number of invocations being requested from this WebSocket to the associated listener, not the number of messages. Sometimes a message may be delivered to the listener in a single invocation, but not always. For example, Ping, Pong and Close messages are delivered in a single invocation of onPing, onPong and onClose methods respectively. However, whether or not Text and Binary messages are delivered in a single invocation of onText and onBinary methods depends on the boolean argument (last) of these methods. If last is false, then there is more to a message than has been delivered to the invocation.

Here is an example of a listener that requests invocations, one at a time, until a complete message has been accumulated, and then processes the result:

WebSocket.Listener listener = new WebSocket.Listener() {

        StringBuilder text = new StringBuilder();

        public CompletionStage<?> onText(WebSocket webSocket,
                                         CharSequence message,
                                         boolean last) {
            text.append(message);
            if (last) {
                processCompleteTextMessage(text);
                text = new StringBuilder();
            }
            webSocket.request(1);
            return null;
        }
    ...
    }

Parameters:

n - the number of invocations

Throws:

IllegalArgumentException - if n <= 0

getSubprotocol

String getSubprotocol()

Returns the subprotocol used by this WebSocket.

Returns:: the subprotocol, or an empty string if there's no subprotocol

isOutputClosed

boolean isOutputClosed()

Tells whether this WebSocket's output is closed.

If this method returns true, subsequent invocations will also return true.

Returns:: true if closed, false otherwise

isInputClosed

boolean isInputClosed()

Tells whether this WebSocket's input is closed.

If this method returns true, subsequent invocations will also return true.

Returns:: true if closed, false otherwise

abort

void abort()

Closes this WebSocket's input and output abruptly.

When this method returns both the input and the output will have been closed. Any pending send operations will fail with IOException. Subsequent invocations of abort will have no effect.