（这里做的解析不是很详细，等到走完整个流程再来解析）Dubbo中编解码的工作由Codec2接口的实现来处理，回想一下第一次接触到Codec2相关的内容是在服务端暴露服务的时候，根据具体的协议去暴露服务的步骤中，在DubboProtocol的createServer方法中：
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private ExchangeServer createServer(URL url) { 。。。 //这里url会添加codec=dubbo url = url.addParameter(Constants.CODEC_KEY, Version.isCompatibleVersion() ? COMPATIBLE_CODEC_NAME : DubboCodec.NAME); ExchangeServer server; try { server = Exchangers.bind(url, requestHandler); } 。。。 return server;}
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紧接着进入Exchangers.bind(url, requestHandler);：
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public static ExchangeServer bind(URL url, ExchangeHandler handler) throws RemotingException { //如果url中没有codec属性，就会添加codec=exchange url = url.addParameterIfAbsent(Constants.CODEC_KEY, "exchange"); return getExchanger(url).bind(url, handler);}
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然后会继续进入HeaderExchanger的bind方法：
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public ExchangeServer bind(URL url, ExchangeHandler handler) throws RemotingException { return new HeaderExchangeServer(Transporters.bind(url, new DecodeHandler(new HeaderExchangeHandler(handler))));}
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在这里会创建一个DecodeHandler实例。继续跟踪Transporters的bind方法，会发现直接返回一个NettyServer实例，在NettyServer的父类AbstractEndpoint构造方法初始的时候，会根据url获取一个ChannelCodec，并将其赋值给codec存放到NettyServer的实例中。
我们先看下getChannelCodec(url);方法：
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protected static Codec2 getChannelCodec(URL url) { //获取codecName，不存在的话，默认为telnet String codecName = url.getParameter(Constants.CODEC_KEY, "telnet"); //先看下是不是Codec2的实现，是的话就根据SPI扩展机制获得Codec2扩展的实现 //我们这里默认使用的是DubboCountCodec if (ExtensionLoader.getExtensionLoader(Codec2.class).hasExtension(codecName)) { return ExtensionLoader.getExtensionLoader(Codec2.class).getExtension(codecName); } else { //如果不是Codec2的实现，就去查找Codec的实现 //然后使用CodecAdapter适配器类来转换成Codec2 return new CodecAdapter(ExtensionLoader.getExtensionLoader(Codec.class) .getExtension(codecName)); }}
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这里返回的是Codec2，而Codec这个接口已经被标记为过时。到这里的话，在NettyServer中就会存在一个Codec2的实例了。
在继续往下看到NettyServer中的doOpen()方法，这里是使用Netty的逻辑打开服务并绑定监听服务的地方：
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protected void doOpen() throws Throwable { NettyHelper.setNettyLoggerFactory(); ExecutorService boss = Executors.newCachedThreadPool(new NamedThreadFactory("NettyServerBoss", true)); ExecutorService worker = Executors.newCachedThreadPool(new NamedThreadFactory("NettyServerWorker", true)); ChannelFactory channelFactory = new NioServerSocketChannelFactory(boss, worker, getUrl().getPositiveParameter(Constants.IO_THREADS_KEY, Constants.DEFAULT_IO_THREADS)); bootstrap = new ServerBootstrap(channelFactory);
final NettyHandler nettyHandler = new NettyHandler(getUrl(), this); channels = nettyHandler.getChannels(); bootstrap.setPipelineFactory(new ChannelPipelineFactory() { public ChannelPipeline getPipeline() { //这里的getCodec方法获取到的codec就是在AbstractEndpoint中我们获取到的codec //NettyCodecAdapter，适配器类 NettyCodecAdapter adapter = new NettyCodecAdapter(getCodec() ,getUrl(), NettyServer.this); ChannelPipeline pipeline = Channels.pipeline(); pipeline.addLast("decoder", adapter.getDecoder());//SimpleChannelUpstreamHandler pipeline.addLast("encoder", adapter.getEncoder());//OneToOneEncoder pipeline.addLast("handler", nettyHandler); return pipeline; } }); // bind channel = bootstrap.bind(getBindAddress());}
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这里就在Netty的pipeline中添加了编解码器。这里涉及到Netty的相关流程，可以先了解下Netty3服务端流程简介。
decoder为解码器，是一个SimpleChannelUpstreamHandler，从Socket到Netty中的时候，需要解码，也就是服务提供端接收到消费者的请求的时候，需要解码。
encoder是编码器，是OneToOneEncoder，这个类实现了ChannelDownstreamHandler，从服务提供端发送给服务消费者的时候，需要编码。
nettyHandler实现了ChannelUpstreamHandler, ChannelDownstreamHandler两个，上下的时候都需要处理。
接收到服务消费者的请求的时候，会先执行decoder，然后执行nettyHandler。
发送给消费者的时候，会先执行nettyHandler，然后执行encoder。
dubbo协议头
协议头是16字节的定长数据：
- 2字节short类型的Magic
- 1字节的消息标志位
- 5位序列化id
- 1位心跳还是正常请求
- 1位双向还是单向
- 1位请求还是响应
- 1字节的状态位
- 8字节的消息id
- 4字节数据长度
编码的过程
首先会判断是请求还是响应，代码在ExchangeCodec的encode方法：
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public void encode(Channel channel, ChannelBuffer buffer, Object msg) throws IOException { if (msg instanceof Request) {//Request类型 encodeRequest(channel, buffer, (Request) msg); } else if (msg instanceof Response) {//Response类型 encodeResponse(channel, buffer, (Response) msg); } else {//telenet类型的 super.encode(channel, buffer, msg); }}
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服务提供者对响应信息编码
在服务提供者端一般是对响应来做编码，所以这里重点看下encodeResponse。
encodeResponse：
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protected void encodeResponse(Channel channel, ChannelBuffer buffer, Response res) throws IOException { try { //序列化方式 //也是根据SPI扩展来获取，url中没指定的话默认使用hessian2 Serialization serialization = getSerialization(channel); //长度为16字节的数组，协议头 byte[] header = new byte[HEADER_LENGTH]; //魔数0xdabb Bytes.short2bytes(MAGIC, header); //序列化方式 header[2] = serialization.getContentTypeId(); //心跳消息还是正常消息 if (res.isHeartbeat()) header[2] |= FLAG_EVENT; //响应状态 byte status = res.getStatus(); header[3] = status; //设置请求id Bytes.long2bytes(res.getId(), header, 4); //buffer为1024字节的ChannelBuffer //获取buffer的写入位置 int savedWriteIndex = buffer.writerIndex(); //需要再加上协议头的长度之后，才是正确的写入位置 buffer.writerIndex(savedWriteIndex + HEADER_LENGTH); ChannelBufferOutputStream bos = new ChannelBufferOutputStream(buffer); ObjectOutput out = serialization.serialize(channel.getUrl(), bos); // 对响应信息或者错误消息进行编码 if (status == Response.OK) { if (res.isHeartbeat()) { //心跳 encodeHeartbeatData(channel, out, res.getResult()); } else { //正常响应 encodeResponseData(channel, out, res.getResult()); } } //错误消息 else out.writeUTF(res.getErrorMessage()); out.flushBuffer(); bos.flush(); bos.close(); //写出去的消息的长度 int len = bos.writtenBytes(); //查看消息长度是否过长 checkPayload(channel, len); Bytes.int2bytes(len, header, 12); //重置写入的位置 buffer.writerIndex(savedWriteIndex); //向buffer中写入消息头 buffer.writeBytes(header); // write header. //buffer写出去的位置从writerIndex开始，加上header长度，加上数据长度 buffer.writerIndex(savedWriteIndex + HEADER_LENGTH + len); } catch (Throwable t) { // 发送失败信息给Consumer，否则Consumer只能等超时了 if (! res.isEvent() && res.getStatus() != Response.BAD_RESPONSE) { try { // FIXME 在Codec中打印出错日志？在IoHanndler的caught中统一处理？ logger.warn("Fail to encode response: " + res + ", send bad_response info instead, cause: " + t.getMessage(), t);
Response r = new Response(res.getId(), res.getVersion()); r.setStatus(Response.BAD_RESPONSE); r.setErrorMessage("Failed to send response: " + res + ", cause: " + StringUtils.toString(t)); channel.send(r);
return; } catch (RemotingException e) { logger.warn("Failed to send bad_response info back: " + res + ", cause: " + e.getMessage(), e); } }
// 重新抛出收到的异常 if (t instanceof IOException) { throw (IOException) t; } else if (t instanceof RuntimeException) { throw (RuntimeException) t; } else if (t instanceof Error) { throw (Error) t; } else { throw new RuntimeException(t.getMessage(), t); } }}
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服务消费者对请求信息编码
消费者端暂先不做解析
解码的过程
服务提供者对请求消息的解码
decode方法一次只会解析一个完整的dubbo协议包，但是每次收到的协议包不一定是完整的，或者有可能是多个协议包。看下代码解析，首先看NettyCodecAdapter的内部类InternalDecoder的messageReceived方法：
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public void messageReceived(ChannelHandlerContext ctx, MessageEvent event) throws Exception { Object o = event.getMessage(); if (! (o instanceof ChannelBuffer)) { ctx.sendUpstream(event); return; }
ChannelBuffer input = (ChannelBuffer) o; int readable = input.readableBytes(); if (readable <= 0) { return; }
com.alibaba.dubbo.remoting.buffer.ChannelBuffer message; if (buffer.readable()) { if (buffer instanceof DynamicChannelBuffer) { buffer.writeBytes(input.toByteBuffer()); message = buffer; } else { int size = buffer.readableBytes() + input.readableBytes(); message = com.alibaba.dubbo.remoting.buffer.ChannelBuffers.dynamicBuffer( size > bufferSize ? size : bufferSize); message.writeBytes(buffer, buffer.readableBytes()); message.writeBytes(input.toByteBuffer()); } } else { message = com.alibaba.dubbo.remoting.buffer.ChannelBuffers.wrappedBuffer( input.toByteBuffer()); }
NettyChannel channel = NettyChannel.getOrAddChannel(ctx.getChannel(), url, handler); Object msg; //读索引 int saveReaderIndex; try { do { saveReaderIndex = message.readerIndex(); try { //解码 msg = codec.decode(channel, message); } catch (IOException e) { buffer = com.alibaba.dubbo.remoting.buffer.ChannelBuffers.EMPTY_BUFFER; throw e; } //不完整的协议包 if (msg == Codec2.DecodeResult.NEED_MORE_INPUT) { //重置读索引 message.readerIndex(saveReaderIndex); //跳出循环，之后在finally中把message赋值给buffer保存起来，等到下次接收到数据包的时候会追加到buffer的后面 break; } else {//有多个协议包，触发messageReceived事件 if (saveReaderIndex == message.readerIndex()) { buffer = com.alibaba.dubbo.remoting.buffer.ChannelBuffers.EMPTY_BUFFER; throw new IOException("Decode without read data."); } if (msg != null) { Channels.fireMessageReceived(ctx, msg, event.getRemoteAddress()); } } } while (message.readable()); } finally { if (message.readable()) { message.discardReadBytes(); buffer = message; } else { buffer = com.alibaba.dubbo.remoting.buffer.ChannelBuffers.EMPTY_BUFFER; } NettyChannel.removeChannelIfDisconnected(ctx.getChannel()); }}
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继续看codec.decode(channel, message);这里是DubboCountCodec的decode方法：
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public Object decode(Channel channel, ChannelBuffer buffer) throws IOException { //当前的读索引记录下来 int save = buffer.readerIndex(); //多消息 MultiMessage result = MultiMessage.create(); do { //解码消息 Object obj = codec.decode(channel, buffer); //不是完整的协议包 if (Codec2.DecodeResult.NEED_MORE_INPUT == obj) { buffer.readerIndex(save); break; } else {//多个协议包 result.addMessage(obj); logMessageLength(obj, buffer.readerIndex() - save); save = buffer.readerIndex(); } } while (true); if (result.isEmpty()) { return Codec2.DecodeResult.NEED_MORE_INPUT; } if (result.size() == 1) { return result.get(0); } return result;}
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继续看ExchangeCodec的decode方法：
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public Object decode(Channel channel, ChannelBuffer buffer) throws IOException { //可读字节数 int readable = buffer.readableBytes(); byte[] header = new byte[Math.min(readable, HEADER_LENGTH)]; //协议头 buffer.readBytes(header); //解码 return decode(channel, buffer, readable, header);}
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解码decode：
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protected Object decode(Channel channel, ChannelBuffer buffer, int readable, byte[] header) throws IOException { //检查魔数. if (readable > 0 && header[0] != MAGIC_HIGH || readable > 1 && header[1] != MAGIC_LOW) { int length = header.length; if (header.length < readable) { header = Bytes.copyOf(header, readable); buffer.readBytes(header, length, readable - length); } for (int i = 1; i < header.length - 1; i ++) { if (header[i] == MAGIC_HIGH && header[i + 1] == MAGIC_LOW) { buffer.readerIndex(buffer.readerIndex() - header.length + i); header = Bytes.copyOf(header, i); break; } } //telenet return super.decode(channel, buffer, readable, header); } //不完整的包 if (readable < HEADER_LENGTH) { return DecodeResult.NEED_MORE_INPUT; }
//数据长度 int len = Bytes.bytes2int(header, 12); checkPayload(channel, len);
int tt = len + HEADER_LENGTH; if( readable < tt ) { return DecodeResult.NEED_MORE_INPUT; }
// limit input stream. ChannelBufferInputStream is = new ChannelBufferInputStream(buffer, len);
try { //解码数据 return decodeBody(channel, is, header); } finally { if (is.available() > 0) { try { StreamUtils.skipUnusedStream(is); } catch (IOException e) { } } }}
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decodeBody解析数据部分：
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protected Object decodeBody(Channel channel, InputStream is, byte[] header) throws IOException { byte flag = header[2], proto = (byte) (flag & SERIALIZATION_MASK); //获取序列化方式 Serialization s = CodecSupport.getSerialization(channel.getUrl(), proto); //反序列化 ObjectInput in = s.deserialize(channel.getUrl(), is); //获取请求id long id = Bytes.bytes2long(header, 4); //这里是解码响应数据 if ((flag & FLAG_REQUEST) == 0) { //response的id设为来时候的Request的id，这样才能对上暗号 Response res = new Response(id); //判断是什么类型请求 if ((flag & FLAG_EVENT) != 0) { res.setEvent(Response.HEARTBEAT_EVENT); } //获取状态 byte status = header[3]; res.setStatus(status); if (status == Response.OK) { try { Object data; if (res.isHeartbeat()) { //解码心跳数据 data = decodeHeartbeatData(channel, in); } else if (res.isEvent()) { //事件 data = decodeEventData(channel, in); } else { //响应 data = decodeResponseData(channel, in, getRequestData(id)); } res.setResult(data); } catch (Throwable t) { res.setStatus(Response.CLIENT_ERROR); res.setErrorMessage(StringUtils.toString(t)); } } else { res.setErrorMessage(in.readUTF()); } return res; } else {//这是解码请求数据 // request的id Request req = new Request(id); req.setVersion("2.0.0"); req.setTwoWay((flag & FLAG_TWOWAY) != 0); if ((flag & FLAG_EVENT) != 0) { req.setEvent(Request.HEARTBEAT_EVENT); } try { Object data; if (req.isHeartbeat()) { //心跳 data = decodeHeartbeatData(channel, in); } else if (req.isEvent()) { //事件 data = decodeEventData(channel, in); } else { //请求 data = decodeRequestData(channel, in); } req.setData(data); } catch (Throwable t) { // bad request req.setBroken(true); req.setData(t); } return req; }}
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具体的解码细节交给底层解码器，这里是使用的hessian2。
服务消费者对响应消息的解码
暂先不做解释。
时间： 2024-08-04 12:38:41