PrefaceDecoder Class — netty Architecture

Source Code

codec-http2/src/main/java/io/netty/handler/codec/http2/Http2ConnectionHandler.java lines 226–394

    private final class PrefaceDecoder extends BaseDecoder {
        private ByteBuf clientPrefaceString;
        private boolean prefaceSent;

        PrefaceDecoder(ChannelHandlerContext ctx) throws Exception {
            clientPrefaceString = clientPrefaceString(encoder.connection());
            // This handler was just added to the context. In case it was handled after
            // the connection became active, send the connection preface now.
            sendPreface(ctx);
        }

        @Override
        public boolean prefaceSent() {
            return prefaceSent;
        }

        @Override
        public void decode(ChannelHandlerContext ctx, ByteBuf in, List<Object> out) throws Exception {
            try {
                if (ctx.channel().isActive() && readClientPrefaceString(in) && verifyFirstFrameIsSettings(in)) {
                    // After the preface is read, it is time to hand over control to the post initialized decoder.
                    byteDecoder = new FrameDecoder();
                    byteDecoder.decode(ctx, in, out);
                }
            } catch (Throwable e) {
                if (byteDecoder != null) {
                    // Skip all bytes before we report the exception as
                    in.skipBytes(in.readableBytes());
                }
                onError(ctx, false, e);
            }
        }

        @Override
        public void channelActive(ChannelHandlerContext ctx) throws Exception {
            // The channel just became active - send the connection preface to the remote endpoint.
            sendPreface(ctx);

            if (flushPreface) {
                // As we don't know if any channelReadComplete() events will be triggered at all we need to ensure we
                // also flush. Otherwise the remote peer might never see the preface / settings frame.
                // See https://github.com/netty/netty/issues/12089
                ctx.flush();
            }
        }

        @Override
        public void channelInactive(ChannelHandlerContext ctx) throws Exception {
            cleanup();
            super.channelInactive(ctx);
        }

        /**
         * Releases the {@code clientPrefaceString}. Any active streams will be left in the open.
         */
        @Override
        public void handlerRemoved(ChannelHandlerContext ctx) throws Exception {
            cleanup();
        }

        /**
         * Releases the {@code clientPrefaceString}. Any active streams will be left in the open.
         */
        private void cleanup() {
            if (clientPrefaceString != null) {
                clientPrefaceString.release();
                clientPrefaceString = null;
            }
        }

        /**
         * Decodes the client connection preface string from the input buffer.
         *
         * @return {@code true} if processing of the client preface string is complete. Since client preface strings can
         *         only be received by servers, returns true immediately for client endpoints.
         */
        private boolean readClientPrefaceString(ByteBuf in) throws Http2Exception {
            if (clientPrefaceString == null) {
                return true;
            }