客户端响应解码整体流程：
1 NettyCodecAdapter$InternalDecoder.decode(ChannelHandlerContext ctx, ByteBuf input, List<Object> out) 2 -->new NettyBackedChannelBuffer(ByteBuf buffer) // 创建一个buffer 3 -->NettyChannel.getOrAddChannel(io.netty.channel.Channel ch, URL url, ChannelHandler handler) 4 -->DubboCountCodec.decode(Channel channel, ChannelBuffer buffer) 5 -->ExchangeCodec.decode(Channel channel, ChannelBuffer buffer) 6 -->buffer.readBytes(header); //读取header byte[] 7 -->decode(Channel channel, ChannelBuffer buffer, int readable, byte[] header) 8 -->检查魔数、检查总长度是否大于等于16 9 -->获取请求体长度 10 -->new ChannelBufferInputStream(buffer, len) 11 -->DubboCodec.decodeBody(Channel channel, InputStream is, byte[] header) 12 -->CodecSupport.getSerialization(URL url, Byte id) //解析出请求头header[2]中的序列化ID,根据该ID获取与请求编码相同的序列化协议 13 -->Bytes.bytes2long(header, 4) //获取respID 14 <!-- 之后创建一个新的Response对象，将respID及后续解析出来的各种resp属性塞入该对象中 --> 15 -->new DecodeableRpcResult(Channel channel, Response response, InputStream is, Invocation invocation, byte id) 16 -->DecodeableRpcResult.decode() 17 -->decode(Channel channel, InputStream input) //解析请求体参数并将其构造为一个DecodeableRpcResult，最终塞到Request对象的data属性中 18 -->new Hessian2ObjectInput(InputStream is) 19 -->反序列化：in.readObject()
与 12.2 服务端请求解码 极其相似。
不同的地方是：
1 protected Object decodeBody(Channel channel, InputStream is, byte[] header) throws IOException { 2 byte flag = header[2], proto = (byte) (flag & SERIALIZATION_MASK); 3 Serialization s = CodecSupport.getSerialization(channel.getUrl(), proto); 4 // get request id. 5 long id = Bytes.bytes2long(header, 4); 6 if ((flag & FLAG_REQUEST) == 0) {// 解码服务端的响应 7 // decode response. 8 Response res = new Response(id); 9 if ((flag & FLAG_EVENT) != 0) { 10 res.setEvent(Response.HEARTBEAT_EVENT); 11 } 12 // get status. 13 byte status = header[3]; 14 res.setStatus(status); 15 if (status == Response.OK) { 16 try { 17 Object data; 18 if (res.isHeartbeat()) { 19 data = decodeHeartbeatData(channel, deserialize(s, channel.getUrl(), is)); 20 } else if (res.isEvent()) { 21 data = decodeEventData(channel, deserialize(s, channel.getUrl(), is)); 22 } else { 23 DecodeableRpcResult result; 24 if (channel.getUrl().getParameter( 25 Constants.DECODE_IN_IO_THREAD_KEY, 26 Constants.DEFAULT_DECODE_IN_IO_THREAD)) { 27 result = new DecodeableRpcResult(channel, res, is, 28 (Invocation) getRequestData(id), proto); 29 result.decode(); 30 } else { 31 result = new DecodeableRpcResult(channel, res, 32 new UnsafeByteArrayInputStream(readMessageData(is)), 33 (Invocation) getRequestData(id), proto); 34 } 35 data = result; 36 } 37 res.setResult(data); 38 } catch (Throwable t) { 39 if (log.isWarnEnabled()) { 40 log.warn("Decode response failed: " + t.getMessage(), t); 41 } 42 res.setStatus(Response.CLIENT_ERROR); 43 res.setErrorMessage(StringUtils.toString(t)); 44 } 45 } else { 46 res.setErrorMessage(deserialize(s, channel.getUrl(), is).readUTF()); 47 } 48 return res; 49 } else { // 解码客户端的请求 50 // decode request. 51 Request req = new Request(id); 52 req.setVersion("2.0.0"); 53 req.setTwoWay((flag & FLAG_TWOWAY) != 0); 54 if ((flag & FLAG_EVENT) != 0) { 55 req.setEvent(Request.HEARTBEAT_EVENT); 56 } 57 try { 58 Object data; 59 if (req.isHeartbeat()) { 60 data = decodeHeartbeatData(channel, deserialize(s, channel.getUrl(), is)); 61 } else if (req.isEvent()) { 62 data = decodeEventData(channel, deserialize(s, channel.getUrl(), is)); 63 } else { 64 DecodeableRpcInvocation inv; 65 if (channel.getUrl().getParameter( 66 Constants.DECODE_IN_IO_THREAD_KEY, 67 Constants.DEFAULT_DECODE_IN_IO_THREAD)) { 68 inv = new DecodeableRpcInvocation(channel, req, is, proto); 69 inv.decode(); 70 } else { 71 inv = new DecodeableRpcInvocation(channel, req, 72 new UnsafeByteArrayInputStream(readMessageData(is)), proto); 73 } 74 data = inv; 75 } 76 req.setData(data); 77 } catch (Throwable t) { 78 if (log.isWarnEnabled()) { 79 log.warn("Decode request failed: " + t.getMessage(), t); 80 } 81 // bad request 82 req.setBroken(true); 83 req.setData(t); 84 } 85 return req; 86 } 87 } 88 89 private ObjectInput deserialize(Serialization serialization, URL url, InputStream is) 90 throws IOException { 91 return serialization.deserialize(url, is); 92 } 93 94 private byte[] readMessageData(InputStream is) throws IOException { 95 if (is.available() > 0) { 96 byte[] result = new byte[is.available()]; 97 is.read(result); 98 return result; 99 } 100 return new byte[]{}; 101 }
DecodeableRpcResult：
1 public Object decode(Channel channel, InputStream input) throws IOException { 2 ObjectInput in = CodecSupport.getSerialization(channel.getUrl(), serializationType) 3 .deserialize(channel.getUrl(), input); 4 5 byte flag = in.readByte(); 6 switch (flag) { 7 case DubboCodec.RESPONSE_NULL_VALUE: 8 break; 9 case DubboCodec.RESPONSE_VALUE://这个值是响应编码是编码进来的，用来表示响应的返回类型 10 try { 11 Type[] returnType = RpcUtils.getReturnTypes(invocation); 12 setValue(returnType == null || returnType.length == 0 ? in.readObject() : 13 (returnType.length == 1 ? in.readObject((Class<?>) returnType[0]) 14 : in.readObject((Class<?>) returnType[0], returnType[1]))); 15 } catch (ClassNotFoundException e) { 16 throw new IOException(StringUtils.toString("Read response data failed.", e)); 17 } 18 break; 19 case DubboCodec.RESPONSE_WITH_EXCEPTION: 20 try { 21 Object obj = in.readObject(); 22 if (obj instanceof Throwable == false) 23 throw new IOException("Response data error, expect Throwable, but get " + obj); 24 setException((Throwable) obj); 25 } catch (ClassNotFoundException e) { 26 throw new IOException(StringUtils.toString("Read response data failed.", e)); 27 } 28 break; 29 default: 30 throw new IOException("Unknown result flag, expect '0' '1' '2', get " + flag); 31 } 32 return this; 33 }
setValue：设置DecodeableRpcResult的Object result属性。
响应解码结束。