/*
 * Copyright 2016 The Netty Project
 *
 * The Netty Project licenses this file to you under the Apache License, version 2.0 (the
 * "License"); you may not use this file except in compliance with the License. You may obtain a
 * copy of the License at:
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software distributed under the License
 * is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express
 * or implied. See the License for the specific language governing permissions and limitations under
 * the License.
 */

package io.netty.example.http2.helloworld.multiplex.server;

import static io.netty.buffer.Unpooled.copiedBuffer;
import static io.netty.buffer.Unpooled.unreleasableBuffer;
import static io.netty.handler.codec.http.HttpResponseStatus.OK;
import io.netty.buffer.ByteBuf;
import io.netty.buffer.ByteBufUtil;
import io.netty.channel.ChannelDuplexHandler;
import io.netty.channel.ChannelHandler.Sharable;
import io.netty.channel.ChannelHandlerContext;
import io.netty.handler.codec.http2.DefaultHttp2DataFrame;
import io.netty.handler.codec.http2.DefaultHttp2Headers;
import io.netty.handler.codec.http2.DefaultHttp2HeadersFrame;
import io.netty.handler.codec.http2.Http2DataFrame;
import io.netty.handler.codec.http2.Http2Headers;
import io.netty.handler.codec.http2.Http2HeadersFrame;
import io.netty.util.CharsetUtil;

A simple handler that responds with the message "Hello World!".
This example is making use of the "multiplexing" http2 API, where streams are mapped to child
Channels. This API is very experimental and incomplete.
/**
 * A simple handler that responds with the message "Hello World!".
 *
 * <p>This example is making use of the "multiplexing" http2 API, where streams are mapped to child
 * Channels. This API is very experimental and incomplete.
 */
@Sharable
public class HelloWorldHttp2Handler extends ChannelDuplexHandler {

    static final ByteBuf RESPONSE_BYTES = unreleasableBuffer(copiedBuffer("Hello World", CharsetUtil.UTF_8));

    @Override
    public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) throws Exception {
        super.exceptionCaught(ctx, cause);
        cause.printStackTrace();
        ctx.close();
    }

    @Override
    public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception {
        if (msg instanceof Http2HeadersFrame) {
            onHeadersRead(ctx, (Http2HeadersFrame) msg);
        } else if (msg instanceof Http2DataFrame) {
            onDataRead(ctx, (Http2DataFrame) msg);
        } else {
            super.channelRead(ctx, msg);
        }
    }

    @Override
    public void channelReadComplete(ChannelHandlerContext ctx) throws Exception {
        ctx.flush();
    }

    
If receive a frame with end-of-stream set, send a pre-canned response.
/**
     * If receive a frame with end-of-stream set, send a pre-canned response.
     */
    private static void onDataRead(ChannelHandlerContext ctx, Http2DataFrame data) throws Exception {
        if (data.isEndStream()) {
            sendResponse(ctx, data.content());
        } else {
            // We do not send back the response to the remote-peer, so we need to release it.
            data.release();
        }
    }

    
If receive a frame with end-of-stream set, send a pre-canned response.
/**
     * If receive a frame with end-of-stream set, send a pre-canned response.
     */
    private static void onHeadersRead(ChannelHandlerContext ctx, Http2HeadersFrame headers)
            throws Exception {
        if (headers.isEndStream()) {
            ByteBuf content = ctx.alloc().buffer();
            content.writeBytes(RESPONSE_BYTES.duplicate());
            ByteBufUtil.writeAscii(content, " - via HTTP/2");
            sendResponse(ctx, content);
        }
    }

    
Sends a "Hello World" DATA frame to the client.
/**
     * Sends a "Hello World" DATA frame to the client.
     */
    private static void sendResponse(ChannelHandlerContext ctx, ByteBuf payload) {
        // Send a frame for the response status
        Http2Headers headers = new DefaultHttp2Headers().status(OK.codeAsText());
        ctx.write(new DefaultHttp2HeadersFrame(headers));
        ctx.write(new DefaultHttp2DataFrame(payload, true));
    }
}