描述
WebSocket是html5开始浏览器和服务端进行全双工通信的网络技术。在该协议下，与服务端只需要一次握手，之后建立一条快速通道，开始互相传输数据，实际是基于TCP双向全双工，比http半双工提高了很大的性能，常用于网络在线聊天室等。继续netty实例的学习，本期内容主要做WebSocket实例的实现和相关协议的验证。
WebSocket与http比较
| http | WebSocket |
|---|---|
| 半双工，可以双向传输，不能同时传输 | 全双工 |
| 消息冗长繁琐，消息头，消息体，换行... | 对代理、防火墙、路由器透明 |
| http轮询实现推送请求量大，而comet采用长连接 | 无头部、Cookie等 |
| - | ping/pong帧保持链路激活 |
| - | 特点：服务端可以主动传递给客户端，不需要轮询 |
代码示例和运行结果
服务端
服务端比较简单，是一启动一个端口来处理请求。
主程序
import io.netty.bootstrap.ServerBootstrap;
import io.netty.channel.Channel;
import io.netty.channel.ChannelInitializer;
import io.netty.channel.EventLoopGroup;
import io.netty.channel.nio.NioEventLoopGroup;
import io.netty.channel.socket.SocketChannel;
import io.netty.channel.socket.nio.NioServerSocketChannel;
import io.netty.handler.codec.http.HttpObjectAggregator;
import io.netty.handler.codec.http.HttpServerCodec;
import io.netty.handler.stream.ChunkedWriteHandler;
import org.junit.Test;
public class NettyWebSocketServer {
public void run(final int port) {
EventLoopGroup bossGroup = new NioEventLoopGroup();
EventLoopGroup workerGroup = new NioEventLoopGroup();
try {
ServerBootstrap bootstrap = new ServerBootstrap();
bootstrap.group(bossGroup, workerGroup)
.channel(NioServerSocketChannel.class)
.childHandler(new ChannelInitializer<SocketChannel>() {
@Override
protected void initChannel(SocketChannel ch) throws Exception {
ch.pipeline()
.addLast(new HttpServerCodec())
.addLast(new HttpObjectAggregator(65535))
.addLast(new ChunkedWriteHandler())
.addLast(new WebSocketServerHandler());
}
});
Channel ch = bootstrap.bind(port).sync().channel();
System.out.println("websocket @" + port);
ch.closeFuture().sync();
} catch (Exception e) {
e.printStackTrace();
}
}
@Test
public void runServer() {
run(23123);
}
}
请求处理handler
核心处理WebSocket请求，重点地方加了注释
import io.netty.buffer.ByteBufUtil;
import io.netty.channel.ChannelFuture;
import io.netty.channel.ChannelFutureListener;
import io.netty.channel.ChannelHandlerContext;
import io.netty.channel.SimpleChannelInboundHandler;
import io.netty.handler.codec.http.*;
import io.netty.handler.codec.http.websocketx.*;
import java.time.LocalDateTime;
import java.util.concurrent.TimeUnit;
public class WebSocketServerHandler extends SimpleChannelInboundHandler<Object> {
private WebSocketServerHandshaker handshaker;
@Override
protected void channelRead0(ChannelHandlerContext ctx, Object msg) throws Exception {
//首次请求之后先进行握手，通过http请求来实现
if (msg instanceof FullHttpRequest) {
handleHttpRequest(ctx, (FullHttpRequest) msg);
} else if (msg instanceof WebSocketFrame) {
handleWebSocketRequest(ctx, (WebSocketFrame) msg);
}
}
private void handleHttpRequest(ChannelHandlerContext ctx, FullHttpRequest request) {
//解码http失败返回
if (!request.decoderResult().isSuccess()) {
sendResponse(ctx, request, new DefaultFullHttpResponse(request.protocolVersion(), HttpResponseStatus.BAD_REQUEST, ctx.alloc().buffer()));
return;
}
if (!HttpMethod.GET.equals(request.method())) {
sendResponse(ctx, request, new DefaultFullHttpResponse(request.protocolVersion(), HttpResponseStatus.FORBIDDEN, ctx.alloc().buffer()));
return;
}
//参数分别是ws地址，子协议，是否扩展，最大frame长度
WebSocketServerHandshakerFactory factory = new WebSocketServerHandshakerFactory(getWebSocketLocation(request), null, true, 5 * 1024 * 1024);
handshaker = factory.newHandshaker(request);
if (handshaker == null) {
WebSocketServerHandshakerFactory.sendUnsupportedVersionResponse(ctx.channel());
} else {
handshaker.handshake(ctx.channel(), request);
}
}
//SSL支持采用wss://
private String getWebSocketLocation(FullHttpRequest request) {
String location = request.headers().get(HttpHeaderNames.HOST) + "/websocket";
return "ws://" + location;
}
private void handleWebSocketRequest(ChannelHandlerContext ctx, WebSocketFrame frame) {
//关闭
if (frame instanceof CloseWebSocketFrame) {
handshaker.close(ctx.channel(), (CloseWebSocketFrame) frame.retain());
return;
}
//握手 PING/PONG
if (frame instanceof PingWebSocketFrame) {
ctx.write(new PongWebSocketFrame(frame.content().retain()));
return;
}
//文本接收和发送
if (frame instanceof TextWebSocketFrame) {
String recv = ((TextWebSocketFrame) frame).text();
String text = "now@" + LocalDateTime.now() + "\n recv:" + recv;
//这里加了个循环，每隔一秒服务端主动发送内容给客户端
for (int i = 0; i < 5; i++) {
String res = i + "-" + text;
try {
TimeUnit.SECONDS.sleep(1);
} catch (InterruptedException e) {
e.printStackTrace();
}
ctx.writeAndFlush(new TextWebSocketFrame(res));
}
System.out.println(recv);
return;
}
if (frame instanceof BinaryWebSocketFrame) {
ctx.write(frame.retain());
}
}
@Override
public void channelReadComplete(ChannelHandlerContext ctx) throws Exception {
ctx.flush();
}
private void sendResponse(ChannelHandlerContext ctx, FullHttpRequest req, FullHttpResponse resp) {
HttpResponseStatus status = resp.status();
if (status != HttpResponseStatus.OK) {
ByteBufUtil.writeUtf8(resp.content(), status.toString());
HttpUtil.setContentLength(req, resp.content().readableBytes());
}
boolean keepAlive = HttpUtil.isKeepAlive(req) && status == HttpResponseStatus.OK;
HttpUtil.setKeepAlive(req, keepAlive);
ChannelFuture future = ctx.write(resp);
if (!keepAlive) {
future.addListener(ChannelFutureListener.CLOSE);
}
}
@Override
public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) throws Exception {
cause.printStackTrace();
ctx.close();
}
}
客户端
客户端使用了html来实现，可以直接在浏览器打开，代码比较简单，不做多的介绍。本地使用注意ws地址和服务端的一致。
<html>
<head>
<meta charset="UTF-8">
</head>
<body>
<form onsubmit="return false;">
<input type="text" name="message" value="test"/>
<br/>
<input type="button" value="send", onclick="send(this.form.message.value)"/>
<hr/>
resp:
<br/>
<textarea id="responseText" style="width: 200px;height:300px;"></textarea>
</form>
</form>
</body>
<script type="text/javascript">
var socket;
if (!window.WebSocket) {
window.WebSocket = window.MozWebSocket;
}
if (window.WebSocket) {
socket = new WebSocket("ws://127.0.0.1:23123/websocket");
socket.onmessage = function (ev) {
var ta = document.getElementById('responseText');
ta.value = '';
ta.value = ev.data;
}
socket.onopen = function (ev) {
var ta = document.getElementById('responseText');
ta.value = 'start open websocket ...';
}
socket.onclose = function (ev) {
var ta = document.getElementById('responseText');
ta.value = '';
ta.value = 'close websocket ...';
}
}else {
alert('not support websocket !')
}
function send(msg) {
if (!window.WebSocket) {
return;
}
if (socket.readyState == WebSocket.OPEN) {
socket.send(msg);
}else {
alert('connect fail !')
}
}
</script>
</html>
试验结果
-
请求抓包说明
ws请求
如图中，首先是TCP三次握手，然后HTTP请求，建立WebSocket连接。之后客户端请求一次，然后服务端每隔1秒给发送内容到客户端。
keepAlive
上图是空闲时候的keepAlive调用 -
客户端调用
服务端关闭的时候效果
服务端主动发送的效果
上图是服务端主动发送的效果，随着内容不同数据会变化。
参考资料
[1]示例原始地址:github
[2]《Netty权威指南(第二版)》P213
结语
以上就是本期的内容，后面有时间会继续netty相关实例的文章，确实在网络方面有很多新的收获。
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