PerMessageDeflateDecoder Class — netty Architecture

Source Code

codec-http/src/main/java/io/netty/handler/codec/http/websocketx/extensions/compression/PerMessageDeflateDecoder.java lines 31–100

class PerMessageDeflateDecoder extends DeflateDecoder {

    private boolean compressing;

    /**
     * Constructor
     *
     * @param noContext true to disable context takeover.
     * @param maxAllocation
     *             maximum size of the decompression buffer. Must be >= 0. If zero, maximum size is not limited.
     */
    PerMessageDeflateDecoder(boolean noContext, int maxAllocation) {
        super(noContext, WebSocketExtensionFilter.NEVER_SKIP, maxAllocation);
    }

    /**
     * Constructor
     *
     * @param noContext true to disable context takeover.
     * @param extensionDecoderFilter extension decoder for per message deflate decoder.
     * @param maxAllocation
     *            maximum size of the decompression buffer. Must be >= 0. If zero, maximum size is not limited.
     */
    PerMessageDeflateDecoder(boolean noContext, WebSocketExtensionFilter extensionDecoderFilter, int maxAllocation) {
        super(noContext, extensionDecoderFilter, maxAllocation);
    }

    @Override
    public boolean acceptInboundMessage(Object msg) throws Exception {
        if (!super.acceptInboundMessage(msg)) {
            return false;
        }

        WebSocketFrame wsFrame = (WebSocketFrame) msg;
        if (extensionDecoderFilter().mustSkip(wsFrame)) {
            if (compressing) {
                throw new IllegalStateException("Cannot skip per message deflate decoder, compression in progress");
            }
            return false;
        }

        return ((wsFrame instanceof TextWebSocketFrame || wsFrame instanceof BinaryWebSocketFrame) &&
                (wsFrame.rsv() & WebSocketExtension.RSV1) > 0) ||
               (wsFrame instanceof ContinuationWebSocketFrame && compressing);
    }

    @Override
    protected int newRsv(WebSocketFrame msg) {
        return (msg.rsv() & WebSocketExtension.RSV1) > 0?
                msg.rsv() ^ WebSocketExtension.RSV1 : msg.rsv();
    }

    @Override
    protected boolean appendFrameTail(WebSocketFrame msg) {
        return msg.isFinalFragment();
    }

    @Override
    protected void decode(ChannelHandlerContext ctx, WebSocketFrame msg,
                          List<Object> out) throws Exception {
        super.decode(ctx, msg, out);

        if (msg.isFinalFragment()) {
            compressing = false;
        } else if (msg instanceof TextWebSocketFrame || msg instanceof BinaryWebSocketFrame) {
            compressing = true;
        }
    }

}