WebSocketServerExtensionHandler Class — netty Architecture

Source Code

codec-http/src/main/java/io/netty/handler/codec/http/websocketx/extensions/WebSocketServerExtensionHandler.java lines 52–247

public class WebSocketServerExtensionHandler extends ChannelDuplexHandler {

    private final List<WebSocketServerExtensionHandshaker> extensionHandshakers;

    private final Queue<List<WebSocketServerExtension>> validExtensions = new ArrayDeque<>(4);

    /**
     * Constructor
     *
     * @param extensionHandshakers
     *      The extension handshaker in priority order. A handshaker could be repeated many times
     *      with fallback configuration.
     */
    public WebSocketServerExtensionHandler(WebSocketServerExtensionHandshaker... extensionHandshakers) {
        this.extensionHandshakers = Arrays.asList(checkNonEmpty(extensionHandshakers, "extensionHandshakers"));
    }

    @Override
    public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception {
        // JDK type checks vs non-implemented interfaces costs O(N), where
        // N is the number of interfaces already implemented by the concrete type that's being tested.
        // The only requirement for this call is to make HttpRequest(s) implementors to call onHttpRequestChannelRead
        // and super.channelRead the others, but due to the O(n) cost we perform few fast-path for commonly met
        // singleton and/or concrete types, to save performing such slow type checks.
        if (msg != LastHttpContent.EMPTY_LAST_CONTENT) {
            if (msg instanceof DefaultHttpRequest) {
                // fast-path
                onHttpRequestChannelRead(ctx, (DefaultHttpRequest) msg);
            } else if (msg instanceof HttpRequest) {
                // slow path
                onHttpRequestChannelRead(ctx, (HttpRequest) msg);
            } else {
                super.channelRead(ctx, msg);
            }
        } else {
            super.channelRead(ctx, msg);
        }
    }

    /**
     * This is a method exposed to perform fail-fast checks of user-defined http types.<p>
     * eg:<br>
     * If the user has defined a specific {@link HttpRequest} type i.e.{@code CustomHttpRequest} and
     * {@link #channelRead} can receive {@link LastHttpContent#EMPTY_LAST_CONTENT} {@code msg}
     * types too, can override it like this:
     * <pre>
     *     public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception {
     *         if (msg != LastHttpContent.EMPTY_LAST_CONTENT) {
     *             if (msg instanceof CustomHttpRequest) {
     *                 onHttpRequestChannelRead(ctx, (CustomHttpRequest) msg);
     *             } else {
     *                 // if it's handling other HttpRequest types it MUST use onHttpRequestChannelRead again
     *                 // or have to delegate it to super.channelRead (that can perform redundant checks).
     *                 // If msg is not implementing HttpRequest, it can call ctx.fireChannelRead(msg) on it
     *                 // ...
     *                 super.channelRead(ctx, msg);
     *             }
     *         } else {
     *             // given that msg isn't a HttpRequest type we can just skip calling super.channelRead
     *             ctx.fireChannelRead(msg);
     *         }
     *     }
     * </pre>
     * <strong>IMPORTANT:</strong>
     * It already call {@code super.channelRead(ctx, request)} before returning.
     */
    protected void onHttpRequestChannelRead(ChannelHandlerContext ctx, HttpRequest request) throws Exception {
        List<WebSocketServerExtension> validExtensionsList = null;

        if (WebSocketExtensionUtil.isWebsocketUpgrade(request.headers())) {
            String extensionsHeader = request.headers().getAsString(HttpHeaderNames.SEC_WEBSOCKET_EXTENSIONS);

            if (extensionsHeader != null) {
                List<WebSocketExtensionData> extensions =
                        WebSocketExtensionUtil.extractExtensions(extensionsHeader);
                int rsv = 0;

                for (WebSocketExtensionData extensionData : extensions) {
                    Iterator<WebSocketServerExtensionHandshaker> extensionHandshakersIterator =
                            extensionHandshakers.iterator();
                    WebSocketServerExtension validExtension = null;