基于netty的websocket在channelActive触发时发送数据异常问题分析是怎样的
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####事情起因,用netty实现了websocket,在链接创建成功后发送一个消息给客户端，我们选择在channelActive中发送消息。 可想而知肯定是不行的了 代码如下
EventLoopGroup bossGroup = new NioEventLoopGroup();
EventLoopGroup group = new NioEventLoopGroup();
try {
ServerBootstrap sb = new ServerBootstrap();
sb.option(ChannelOption.SO_BACKLOG, 1024);
// 绑定线程池
sb.group(group, bossGroup)
// 指定使用的channel
.channel(NioServerSocketChannel.class)
// 绑定监听端口
.localAddress(this.port)
.option(ChannelOption.SO_KEEPALIVE, true)
// 绑定客户端连接时候触发操作
.childHandler(new ChannelInitializer() {
@Override
protected void initChannel(SocketChannel ch) throws Exception {
log.info("收到新连接");
ch.pipeline().addLast(new LoggingHandler("DEBUG"));
ch.pipeline().addLast(new IdleStateHandler(60, 0, 0));
//websocket协议本身是基于http协议的，所以这边也要使用http解编码器
ch.pipeline().addLast(new HttpServerCodec());
//以块的方式来写的处理器
ch.pipeline().addLast(new ChunkedWriteHandler());
ch.pipeline().addLast(new HttpObjectAggregator(8192));
ch.pipeline().addLast(new WebSocketServerProtocolHandler("/socket", null, true, 65536 * 10));
ch.pipeline().addLast(new MyWebSocketHandler());
}
});
// 服务器异步创建绑定
ChannelFuture cf = sb.bind().sync();
log.info(NettyServer.class + " 启动正在监听： " + cf.channel().localAddress());
// 关闭服务器通道
cf.channel().closeFuture().sync(); #####排查1:因为没有任何异常，客户端没有收到消息，故先采用wireshark抓包,发现网卡上没有对应的想发送的消息。 为什么网卡没有对应的包呢,经过debug发现如果发送的数据类型是WebSocketFrame在最终发送时候异常了具体代码在HeadContext的write方法中,headcontext是netty的channelpipeline的头部,最终写出时都会从pipeline的尾部链接到头部来执行（pipeline为双向链表） 为什么在channelread中能写信息而在channelActive无法写信息呢,经过分析发现,channelActive的触发是在socketchannel第一次注册的时候发生的具体代码如下:abstrcatchannel中
private void register0(ChannelPromise promise) {
try {
// check if the channel is still open as it could be closed in the mean time when the register
// call was outside of the eventLoop
if (!promise.setUncancellable() || !ensureOpen(promise)) {
return;
}
boolean firstRegistration = neverRegistered;
doRegister();
neverRegistered = false;
registered = true;
// Ensure we call handlerAdded(...) before we actually notify the promise. This is needed as the
// user may already fire events through the pipeline in the ChannelFutureListener.
pipeline.invokeHandlerAddedIfNeeded();
safeSetSuccess(promise);
pipeline.fireChannelRegistered();
// Only fire a channelActive if the channel has never been registered. This prevents firing
// multiple channel actives if the channel is deregistered and re-registered.
if (isActive()) {
if (firstRegistration) {
pipeline.fireChannelActive();
} else if (config().isAutoRead()) {
// This channel was registered before and autoRead() is set. This means we need to begin read
// again so that we process inbound data.
//
// See https://github.com/netty/netty/issues/4805
beginRead();
}
}
} catch (Throwable t) {
// Close the channel directly to avoid FD leak.
closeForcibly();
closeFuture.setClosed();
safeSetFailure(promise, t);
}
}而抓包时发现触发此channelactive时,服务端还未返回websocket的协议握手包(websocket协议是在在http协议上衍生的,会先发一个http get请求然后服务端返回一个为websocket协议的包给客户端)至此问题就真相大白了,在我们添加的WebSocketServerProtocolHandler这个handller中有如下代码
public void handlerAdded(ChannelHandlerContext ctx) {
ChannelPipeline cp = ctx.pipeline();
if (cp.get(WebSocketServerProtocolHandshakeHandler.class) == null) {
// Add the WebSocketHandshakeHandler before this one.
ctx.pipeline().addBefore(ctx.name(), WebSocketServerProtocolHandshakeHandler.class.getName(),
new WebSocketServerProtocolHandshakeHandler(websocketPath, subprotocols,
allowExtensions, maxFramePayloadLength, allowMaskMismatch, checkStartsWith));
}
if (cp.get(Utf8FrameValidator.class) == null) {
// Add the UFT8 checking before this one.
ctx.pipeline().addBefore(ctx.name(), Utf8FrameValidator.class.getName(),
new Utf8FrameValidator());
}
}添加的WebSocketServerProtocolHandshakeHandler中有如下代码
public void channelRead(final ChannelHandlerContext ctx, Object msg) throws Exception {
final FullHttpRequest req = (FullHttpRequest) msg;
if (isNotWebSocketPath(req)) {
ctx.fireChannelRead(msg);
return;
}
try {
if (!GET.equals(req.method())) {
sendHttpResponse(ctx, req, new DefaultFullHttpResponse(HTTP_1_1, FORBIDDEN));
return;
}
final WebSocketServerHandshakerFactory wsFactory = new WebSocketServerHandshakerFactory(
getWebSocketLocation(ctx.pipeline(), req, websocketPath), subprotocols,
allowExtensions, maxFramePayloadSize, allowMaskMismatch);
final WebSocketServerHandshaker handshaker = wsFactory.newHandshaker(req);
if (handshaker == null) {
WebSocketServerHandshakerFactory.sendUnsupportedVersionResponse(ctx.channel());
} else {
final ChannelFuture handshakeFuture = handshaker.handshake(ctx.channel(), req);
handshakeFuture.addListener(new ChannelFutureListener() {
@Override
public void operationComplete(ChannelFuture future) throws Exception {
if (!future.isSuccess()) {
ctx.fireExceptionCaught(future.cause());
} else {
// Kept for compatibility
ctx.fireUserEventTriggered(
WebSocketServerProtocolHandler.ServerHandshakeStateEvent.HANDSHAKE_COMPLETE);
ctx.fireUserEventTriggered(
new WebSocketServerProtocolHandler.HandshakeComplete(
req.uri(), req.headers(), handshaker.selectedSubprotocol()));
}
}
});
WebSocketServerProtocolHandler.setHandshaker(ctx.channel(), handshaker);
ctx.pipeline().replace(this, "WS403Responder",
WebSocketServerProtocolHandler.forbiddenHttpRequestResponder());
}
} finally {
req.release();
}
}接受握手信息时候会添加两个handler 为websocket协议信息的编码和解码handler
public final ChannelFuture handshake(Channel channel, FullHttpRequest req,
HttpHeaders responseHeaders, final ChannelPromise promise) {
if (logger.isDebugEnabled()) {
logger.debug("{} WebSocket version {} server handshake", channel, version());
}
FullHttpResponse response = newHandshakeResponse(req, responseHeaders);
ChannelPipeline p = channel.pipeline();
if (p.get(HttpObjectAggregator.class) != null) {
p.remove(HttpObjectAggregator.class);
}
if (p.get(HttpContentCompressor.class) != null) {
p.remove(HttpContentCompressor.class);
}
ChannelHandlerContext ctx = p.context(HttpRequestDecoder.class);
final String encoderName;
if (ctx == null) {
// this means the user use a HttpServerCodec
ctx = p.context(HttpServerCodec.class);
if (ctx == null) {
promise.setFailure(
new IllegalStateException("No HttpDecoder and no HttpServerCodec in the pipeline"));
return promise;
}
p.addBefore(ctx.name(), "wsdecoder", newWebsocketDecoder());
p.addBefore(ctx.name(), "wsencoder", newWebSocketEncoder());
encoderName = ctx.name();
} else {
p.replace(ctx.name(), "wsdecoder", newWebsocketDecoder());
encoderName = p.context(HttpResponseEncoder.class).name();
p.addBefore(encoderName, "wsencoder", newWebSocketEncoder());
}
channel.writeAndFlush(response).addListener(new ChannelFutureListener() {
@Override
public void operationComplete(ChannelFuture future) throws Exception {
if (future.isSuccess()) {
ChannelPipeline p = future.channel().pipeline();
p.remove(encoderName);
promise.setSuccess();
} else {
promise.setFailure(future.cause());
}
}
});
return promise;
}如果想要实现在websocket协议连接成功后发送一个消息给客户端，我们发现在发送握手成功后触发了fireUserEventTriggered，去实现userEventTriggered然后判断evt类型做处理吧 
以上就是基于netty的websocket在channelActive触发时发送数据异常问题分析是怎样的，小编相信有部分知识点可能是我们日常工作会见到或用到的。希望你能通过这篇文章学到更多知识。更多详情敬请关注创新互联行业资讯频道。
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