Netty实战（十四）

一、初始化 ChannelPipeline

我们之前说过为了将 ChannelHandler 安装到 ChannelPipeline 中，需要扩展了ChannelInitializer，并实现 initChannel()方法。

下面我们演示一下：

import io.netty.channel.Channel;
import io.netty.channel.ChannelInitializer;
import io.netty.channel.ChannelPipeline;
import io.netty.channel.group.ChannelGroup;
import io.netty.handler.codec.http.HttpObjectAggregator;
import io.netty.handler.codec.http.HttpServerCodec;
import io.netty.handler.codec.http.websocketx.WebSocketServerProtocolHandler;
import io.netty.handler.stream.ChunkedWriteHandler;

/**
 * Author: lhd
 * Data: 2023/6/12
 * Annotate: 初始化 ChannelPipeline
 */
public class ChatServerInitializer extends ChannelInitializer<Channel> {
    private final ChannelGroup group;
    public ChatServerInitializer(ChannelGroup group) {
        this.group = group;
    }
    @Override
    protected void initChannel(Channel ch) throws Exception { 
        ChannelPipeline pipeline = ch.pipeline();
        //将所有需要的ChannelHandler 添加到 ChannelPipeline 中
        pipeline.addLast(new HttpServerCodec());
        pipeline.addLast(new ChunkedWriteHandler());
        pipeline.addLast(new HttpObjectAggregator(64 * 1024));
        pipeline.addLast(new HttpRequestHandler("/ws"));
        pipeline.addLast(new WebSocketServerProtocolHandler("/ws"));
        pipeline.addLast(new TextWebSocketFrameHandler(group));
    }
}

我们对于 initChannel()方法的调用，安装所有必需的 ChannelHandler 来设置该新注册的 Channel 的 ChannelPipeline。那么我们安装的这些ChannelHandler 有什么用呢？

ChannelHandler	说 明
HttpServerCodec	将字节解码为 HttpRequest、HttpContent 和 LastHttpContent。并将 HttpRequest、HttpContent 和 LastHttpContent 编码为字节
ChunkedWriteHandler	写入一个文件的内容
HttpObjectAggregator	将一个 HttpMessage 和跟随它的多个 HttpContent 聚合为单个 FullHttpRequest 或者 FullHttpResponse（取决于它是被用来处理请求还是响应）。安装了这个之后，ChannelPipeline 中的下一个 ChannelHandler 将只会收到完整的 HTTP 请求或响应
HttpRequestHandler	处理 FullHttpRequest（那些不发送到/ws URI 的请求）
WebSocketServerProtocolHandler	按照 WebSocket 规范的要求，处理 WebSocket 升级握手、PingWebSocketFrame 、PongWebSocketFrame 和CloseWebSocketFrame
TextWebSocketFrameHandler	处理 TextWebSocketFrame 和握手完成事件

Netty 的 WebSocketServerProtocolHandler 处理了所有委托管理的 WebSocket帧类型以及升级握手本身。如果握手成功，那么所需的 ChannelHandler 将会被添加到ChannelPipeline中，而那些不再需要的ChannelHandler 则将会被移除。

WebSocket 协议升级之前的 ChannelPipeline 的状态如下图所示。这代表了刚刚被ChatServerInitializer 初始化之后的 ChannelPipeline。

WebSocket 协议升级完成之后，WebSocketServerProtocolHandler 将会把 HttpRequestDecoder 替换为 WebSocketFrameDecoder，把 HttpResponseEncoder 替换为WebSocketFrameEncoder。为了性能最大化，它将移除任何不再被 WebSocket 连接所需要的ChannelHandler。其中也包括 HttpObjectAggregator 和 HttpRequestHandler

下图展示了上面操作完成之后的ChannelPipeline，Netty目前支持 4个版本的WebSocket协议，它们每个都具有自己的实现类。Netty将会根据客户端/浏览器所支持的版本 ，自动地选择正确版本WebSocketFrameDecoder和WebSocketFrameEncoder。

二、引导

我们来写一个引导服务器：

import io.netty.bootstrap.ServerBootstrap;
import io.netty.channel.Channel;
import io.netty.channel.ChannelFuture;
import io.netty.channel.ChannelInitializer;
import io.netty.channel.EventLoopGroup;
import io.netty.channel.group.ChannelGroup;
import io.netty.channel.group.DefaultChannelGroup;
import io.netty.channel.nio.NioEventLoopGroup;
import io.netty.channel.socket.nio.NioServerSocketChannel;
import io.netty.util.concurrent.ImmediateEventExecutor;

import java.net.InetSocketAddress;

/**
 * Author: lhd
 * Data: 2023/6/12
 * Annotate:
 */
public class ChatServer {

    //创建 DefaultChannelGroup，其将保存所有已经连接的WebSocket Channe
    private final ChannelGroup channelGroup = new DefaultChannelGroup(ImmediateEventExecutor.INSTANCE);
    private final EventLoopGroup group = new NioEventLoopGroup();
    private Channel channel;

    //引导服务器
    public ChannelFuture start(InetSocketAddress address) {
        ServerBootstrap bootstrap = new ServerBootstrap();
        bootstrap.group(group)
                .channel(NioServerSocketChannel.class)
                .childHandler(createInitializer(channelGroup));
        ChannelFuture future = bootstrap.bind(address);
        future.syncUninterruptibly();
        channel = future.channel();
        return future;
    }

    //创建 ChatServerInitialize
    protected ChannelInitializer<Channel> createInitializer(ChannelGroup group) {
        return new ChatServerInitializer(group);
    }

    //处理服务器关闭，并释放所有的资源
    public void destroy() {
        if (channel != null) {
            channel.close();
        }
        channelGroup.close();
        group.shutdownGracefully();
    }
    public static void main(String[] args) throws Exception {
        if (args.length != 1) {
            System.err.println("Please give port as argument");
            System.exit(1);
        }
        int port = Integer.parseInt(args[0]);
        final ChatServer endpoint = new ChatServer();
        ChannelFuture future = endpoint.start(new InetSocketAddress(port));
        Runtime.getRuntime().addShutdownHook(new Thread() {
            @Override
            public void run() {
                endpoint.destroy();
            }
        });
        future.channel().closeFuture().syncUninterruptibly();
    }
}

三、加密

处理好服务器后，下一步就是测试和加密，测试我们之前说过这里不再多说。

这里的加密有两步，一是为 ChannelPipeline 加密，二是为 ChatServer 添加加密。

ChannelPipeline 加密：

import io.netty.channel.Channel;
import io.netty.channel.group.ChannelGroup;
import io.netty.handler.ssl.SslContext;
import io.netty.handler.ssl.SslHandler;

/**
 * Author: lhd
 * Data: 2023/6/12
 * Annotate:为 ChannelPipeline 添加加密
 */
public class SecureChatServerInitializer extends ChatServerInitializer {
    private final SslContext context;

    public SecureChatServerInitializer(ChannelGroup group, SslContext context) {
        super(group);
        this.context = context;
    }
    @Override
    protected void initChannel(Channel ch) throws Exception {
        //调用父类的initChannel()方法
        super.initChannel(ch);
        SSLEng.ine engine = context.newEngine(ch.alloc());
        engine.setUseClientMode(false);
        // 将SslHandler 添加到ChannelPipeline 中
        ch.pipeline().addFirst(new SslHandler(engine));
    }
}

ChatServer 添加加密

import io.netty.channel.Channel;
import io.netty.channel.ChannelFuture;
import io.netty.channel.ChannelInitializer;
import io.netty.channel.group.ChannelGroup;
import io.netty.handler.ssl.SslContext;
import io.netty.handler.ssl.util.SelfSignedCertificate;

import java.net.InetSocketAddress;

/**
 * Author: lhd
 * Data: 2023/6/12
 * Annotate:
 */
public class SecureChatServer extends ChatServer {//SecureChatServer 扩展 ChatServer 以支持加密
    private final SslContext context;
    public SecureChatServer(SslContext context) {
        this.context = context;
    }
    @Override
    protected ChannelInitializer<Channel> createInitializer(ChannelGroup group) {
        //返回之前创建的 SecureChatServerInitializer 以启用加密
        return new SecureChatServerInitializer(group, context);
    }
    public static void main(String[] args) throws Exception {
        if (args.length != 1) {
            System.err.println("Please give port as argument");
            System.exit(1);
        }
        int port = Integer.parseInt(args[0]);
        SelfSignedCertificate cert = new SelfSignedCertificate();
        SslContext context = SslContext.newServerContext(cert.certificate(), cert.privateKey());
        final SecureChatServer endpoint = new SecureChatServer(context);
        ChannelFuture future = endpoint.start(new InetSocketAddress(port));
        Runtime.getRuntime().addShutdownHook(new Thread() {
            @Override
            public void run() {
                endpoint.destroy();
            }
        });
        future.channel().closeFuture().syncUninterruptibly();
    }
}