使用SniHandler确定客户端与Netty服务器协商的TLS版本

import io.netty.bootstrap.ServerBootstrap;
import io.netty.channel.*;
import io.netty.channel.nio.NioEventLoopGroup;
import io.netty.channel.socket.SocketChannel;
import io.netty.channel.socket.nio.NioServerSocketChannel;
import io.netty.handler.ssl.SslContext;
import io.netty.handler.ssl.SslContextBuilder;
import io.netty.handler.ssl.SupportedCipherSuiteFilter;
import io.netty.handler.ssl.util.SelfSignedCertificate;

public class TlsServer {

    static final int PORT = Integer.parseInt(System.getProperty("port", "8443"));

    public static void main(String[] args) throws Exception {
        SelfSignedCertificate ssc = new SelfSignedCertificate();
        SslContext sslCtx = SslContextBuilder.forServer(ssc.certificate(), ssc.privateKey())
                .ciphers("TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256", SupportedCipherSuiteFilter.INSTANCE)
                .build();

        EventLoopGroup bossGroup = new NioEventLoopGroup(1);
        EventLoopGroup workerGroup = new NioEventLoopGroup();
        try {
            ServerBootstrap b = new ServerBootstrap();
            b.group(bossGroup, workerGroup)
             .channel(NioServerSocketChannel.class)
             .childHandler(new ChannelInitializer<SocketChannel>() {
                 @Override
                 public void initChannel(SocketChannel ch) throws Exception {
                     ChannelPipeline p = ch.pipeline();
                     p.addLast(sslCtx.newHandler(ch.alloc()));
                     p.addLast(new SniHandler());
                     p.addLast(new SimpleChannelInboundHandler<TlsHandshakeCompletionEvent>() {
                         @Override
                         protected void channelRead0(ChannelHandlerContext ctx, TlsHandshakeCompletionEvent msg) throws Exception {
                             System.out.println("TLS version: " + msg.sslSession().cipherSuite());
                             ctx.fireChannelRead(msg);
                         }
                     });
                 }
             });

            ChannelFuture f = b.bind(PORT).sync();
            f.channel().closeFuture().sync();
        } finally {
            bossGroup.shutdownGracefully();
            workerGroup.shutdownGracefully();
        }
    }

    static class SniHandler extends ChannelInboundHandlerAdapter {
        @Override
        public void userEventTriggered(ChannelHandlerContext ctx, Object evt) throws Exception {
            if (evt instanceof SniEvent) {
                SniEvent sniEvent = (SniEvent) evt;
                System.out.println("Client requested hostname: " + sniEvent.hostname());
                // 根据hostname选择合适的SSL上下文
            }
            super.userEventTriggered(ctx, evt);
        }
    }
}