Http2ClientInitializer.java

package chapter7.recipe1.client;

import static io.netty.util.internal.logging.InternalLogLevel.INFO;
import io.netty.channel.ChannelHandlerAdapter;
import io.netty.channel.ChannelHandlerContext;
import io.netty.channel.ChannelInitializer;
import io.netty.channel.ChannelPipeline;
import io.netty.channel.socket.SocketChannel;
import io.netty.handler.codec.http.DefaultFullHttpRequest;
import io.netty.handler.codec.http.HttpClientCodec;
import io.netty.handler.codec.http.HttpClientUpgradeHandler;
import io.netty.handler.codec.http.HttpMethod;
import io.netty.handler.codec.http.HttpVersion;
import io.netty.handler.codec.http2.DefaultHttp2Connection;
import io.netty.handler.codec.http2.DefaultHttp2FrameReader;
import io.netty.handler.codec.http2.DefaultHttp2FrameWriter;
import io.netty.handler.codec.http2.DelegatingDecompressorFrameListener;
import io.netty.handler.codec.http2.Http2ClientUpgradeCodec;
import io.netty.handler.codec.http2.Http2Connection;
import io.netty.handler.codec.http2.Http2FrameLogger;
import io.netty.handler.codec.http2.Http2FrameReader;
import io.netty.handler.codec.http2.Http2FrameWriter;
import io.netty.handler.codec.http2.Http2InboundFrameLogger;
import io.netty.handler.codec.http2.Http2OutboundFrameLogger;
import io.netty.handler.codec.http2.HttpToHttp2ConnectionHandler;
import io.netty.handler.codec.http2.InboundHttp2ToHttpAdapter;
import io.netty.util.internal.logging.InternalLoggerFactory;

/**
 * Configures the client pipeline to support HTTP/2 frames.
 */
public class Http2ClientInitializer extends ChannelInitializer<SocketChannel> {
    private static final Http2FrameLogger logger =
                    new Http2FrameLogger(INFO, InternalLoggerFactory.getInstance(Http2ClientInitializer.class));
    private final int maxContentLength;
    private HttpToHttp2ConnectionHandler connectionHandler;
    private HttpResponseHandler responseHandler;
    private Http2SettingsHandler settingsHandler;

    public Http2ClientInitializer(int maxContentLength) {        
        this.maxContentLength = maxContentLength;
    }

    @Override
    public void initChannel(SocketChannel ch) throws Exception {
        final Http2Connection connection = new DefaultHttp2Connection(false);
        final Http2FrameWriter frameWriter = frameWriter();
        connectionHandler = new HttpToHttp2ConnectionHandler(connection,
                frameReader(),
                frameWriter,
                new DelegatingDecompressorFrameListener(connection,
                        new InboundHttp2ToHttpAdapter.Builder(connection)
                                .maxContentLength(maxContentLength)
                                .propagateSettings(true)
                                .build()));
        responseHandler = new HttpResponseHandler();
        settingsHandler = new Http2SettingsHandler(ch.newPromise());
        configureClearText(ch);
    }

    public HttpResponseHandler responseHandler() {
        return responseHandler;
    }

    public Http2SettingsHandler settingsHandler() {
        return settingsHandler;
    }

    protected void configureEndOfPipeline(ChannelPipeline pipeline) {
        pipeline.addLast("Http2SettingsHandler", settingsHandler);
        pipeline.addLast("HttpResponseHandler", responseHandler);
    }

   
    /**
     * Configure the pipeline for a cleartext upgrade from HTTP to HTTP/2.
     */
    private void configureClearText(SocketChannel ch) {
        HttpClientCodec sourceCodec = new HttpClientCodec();
        Http2ClientUpgradeCodec upgradeCodec = new Http2ClientUpgradeCodec(connectionHandler);
        HttpClientUpgradeHandler upgradeHandler = new HttpClientUpgradeHandler(sourceCodec, upgradeCodec, 65536);

        ch.pipeline().addLast("Http2SourceCodec", sourceCodec);
        ch.pipeline().addLast("Http2UpgradeHandler", upgradeHandler);
        ch.pipeline().addLast("Http2UpgradeRequestHandler", new UpgradeRequestHandler());
        ch.pipeline().addLast("Logger", new UserEventLogger());
    }

    /**
     * A handler that triggers the cleartext upgrade to HTTP/2 by sending an initial HTTP request.
     */
    private final class UpgradeRequestHandler extends ChannelHandlerAdapter {
        @Override
        public void channelActive(ChannelHandlerContext ctx) throws Exception {
            DefaultFullHttpRequest upgradeRequest =
                    new DefaultFullHttpRequest(HttpVersion.HTTP_1_1, HttpMethod.GET, "/");
            ctx.writeAndFlush(upgradeRequest);

            super.channelActive(ctx);

            // Done with this handler, remove it from the pipeline.
            ctx.pipeline().remove(this);

            Http2ClientInitializer.this.configureEndOfPipeline(ctx.pipeline());
        }
    }

    /**
     * Class that logs any User Events triggered on this channel.
     */
    private static class UserEventLogger extends ChannelHandlerAdapter {
        @Override
        public void userEventTriggered(ChannelHandlerContext ctx, Object evt) throws Exception {
            System.out.println("User Event Triggered: " + evt);
            super.userEventTriggered(ctx, evt);
        }
    }

    private static Http2FrameReader frameReader() {
        return new Http2InboundFrameLogger(new DefaultHttp2FrameReader(), logger);
    }

    private static Http2FrameWriter frameWriter() {
        return new Http2OutboundFrameLogger(new DefaultHttp2FrameWriter(), logger);
    }
}