WebSocket00FrameEncoder Class — netty Architecture

Source Code

codec-http/src/main/java/io/netty/handler/codec/http/websocketx/WebSocket00FrameEncoder.java lines 33–104

@Sharable
public class WebSocket00FrameEncoder extends MessageToMessageEncoder<WebSocketFrame> implements WebSocketFrameEncoder {
    private static final ByteBuf _0X00 = LeakPresenceDetector.staticInitializer(() -> Unpooled.unreleasableBuffer(
            Unpooled.directBuffer(1, 1).writeByte(0x00)).asReadOnly());
    private static final ByteBuf _0XFF = LeakPresenceDetector.staticInitializer(() -> Unpooled.unreleasableBuffer(
            Unpooled.directBuffer(1, 1).writeByte((byte) 0xFF)).asReadOnly());
    private static final ByteBuf _0XFF_0X00 = LeakPresenceDetector.staticInitializer(() -> Unpooled.unreleasableBuffer(
            Unpooled.directBuffer(2, 2).writeByte((byte) 0xFF).writeByte(0x00)).asReadOnly());

    public WebSocket00FrameEncoder() {
        super(WebSocketFrame.class);
    }

    @Override
    protected void encode(ChannelHandlerContext ctx, WebSocketFrame msg, List<Object> out) throws Exception {
        if (msg instanceof TextWebSocketFrame) {
            // Text frame
            ByteBuf data = msg.content();

            out.add(_0X00.duplicate());
            out.add(data.retain());
            out.add(_0XFF.duplicate());
        } else if (msg instanceof CloseWebSocketFrame) {
            // Close frame, needs to call duplicate to allow multiple writes.
            // See https://github.com/netty/netty/issues/2768
            out.add(_0XFF_0X00.duplicate());
        } else {
            // Binary frame
            ByteBuf data = msg.content();
            int dataLen = data.readableBytes();

            ByteBuf buf = ctx.alloc().buffer(5);
            boolean release = true;
            try {
                // Encode type.
                buf.writeByte((byte) 0x80);

                // Encode length.
                int b1 = dataLen >>> 28 & 0x7F;
                int b2 = dataLen >>> 14 & 0x7F;
                int b3 = dataLen >>> 7 & 0x7F;
                int b4 = dataLen & 0x7F;
                if (b1 == 0) {
                    if (b2 == 0) {
                        if (b3 != 0) {
                            buf.writeByte(b3 | 0x80);
                        }
                        buf.writeByte(b4);
                    } else {
                        buf.writeByte(b2 | 0x80);
                        buf.writeByte(b3 | 0x80);
                        buf.writeByte(b4);
                    }
                } else {
                    buf.writeByte(b1 | 0x80);
                    buf.writeByte(b2 | 0x80);
                    buf.writeByte(b3 | 0x80);
                    buf.writeByte(b4);
                }

                // Encode binary data.
                out.add(buf);
                out.add(data.retain());
                release = false;
            } finally {
                if (release) {
                    buf.release();
                }
            }
        }
    }
}