pkg.Unmarshal(len(@data):0) = error:get wrong attachments

[PhilYue]

What happened:

基于 JSON-PRC 改造入参出参，同 #1582 ，在此代码基础上，Server 同时暴露 dubbo 和 jsonrpc协议，Client 消费使用 dubbo协议时，Server 报错如下：

Server Error Log:

2021-11-11T15:14:28.086+0800    ERROR   dubbo/dubbo_codec.go:196        pkg.Unmarshal(len(@data):0) = error:get wrong attachments: 
dubbo.apache.org/dubbo-go/v3/protocol/dubbo/impl.unmarshalRequestBody
        /Users/phil/go/pkg/mod/dubbo.apache.org/dubbo-go/v3@v3.0.0-rc3.0.20211109121610-2ebc38bed562/protocol/dubbo/impl/hessian.go:267
dubbo.apache.org/dubbo-go/v3/protocol/dubbo/impl.HessianSerializer.Unmarshal
        /Users/phil/go/pkg/mod/dubbo.apache.org/dubbo-go/v3@v3.0.0-rc3.0.20211109121610-2ebc38bed562/protocol/dubbo/impl/hessian.go:56
dubbo.apache.org/dubbo-go/v3/protocol/dubbo/impl.(*ProtocolCodec).Decode
        /Users/phil/go/pkg/mod/dubbo.apache.org/dubbo-go/v3@v3.0.0-rc3.0.20211109121610-2ebc38bed562/protocol/dubbo/impl/codec.go:186
dubbo.apache.org/dubbo-go/v3/protocol/dubbo/impl.(*DubboPackage).Unmarshal
        /Users/phil/go/pkg/mod/dubbo.apache.org/dubbo-go/v3@v3.0.0-rc3.0.20211109121610-2ebc38bed562/protocol/dubbo/impl/package.go:93
dubbo.apache.org/dubbo-go/v3/protocol/dubbo.(*DubboCodec).decodeRequest
        /Users/phil/go/pkg/mod/dubbo.apache.org/dubbo-go/v3@v3.0.0-rc3.0.20211109121610-2ebc38bed562/protocol/dubbo/dubbo_codec.go:189
dubbo.apache.org/dubbo-go/v3/protocol/dubbo.(*DubboCodec).Decode
        /Users/phil/go/pkg/mod/dubbo.apache.org/dubbo-go/v3@v3.0.0-rc3.0.20211109121610-2ebc38bed562/protocol/dubbo/dubbo_codec.go:165
dubbo.apache.org/dubbo-go/v3/remoting/getty.(*RpcServerPackageHandler).Read
        /Users/phil/go/pkg/mod/dubbo.apache.org/dubbo-go/v3@v3.0.0-rc3.0.20211109121610-2ebc38bed562/remoting/getty/readwriter.go:104
github.com/apache/dubbo-getty.(*session).handleTCPPackage
        /Users/phil/go/pkg/mod/github.com/apache/dubbo-getty@v1.4.5/session.go:627
github.com/apache/dubbo-getty.(*session).handlePackage
        /Users/phil/go/pkg/mod/github.com/apache/dubbo-getty@v1.4.5/session.go:549
runtime.goexit
        /usr/local/go/src/runtime/asm_amd64.s:1371
dubbo.apache.org/dubbo-go/v3/protocol/dubbo.(*DubboCodec).decodeRequest
        /Users/phil/go/pkg/mod/dubbo.apache.org/dubbo-go/v3@v3.0.0-rc3.0.20211109121610-2ebc38bed562/protocol/dubbo/dubbo_codec.go:196
dubbo.apache.org/dubbo-go/v3/protocol/dubbo.(*DubboCodec).Decode
        /Users/phil/go/pkg/mod/dubbo.apache.org/dubbo-go/v3@v3.0.0-rc3.0.20211109121610-2ebc38bed562/protocol/dubbo/dubbo_codec.go:165
dubbo.apache.org/dubbo-go/v3/remoting/getty.(*RpcServerPackageHandler).Read
        /Users/phil/go/pkg/mod/dubbo.apache.org/dubbo-go/v3@v3.0.0-rc3.0.20211109121610-2ebc38bed562/remoting/getty/readwriter.go:104
github.com/apache/dubbo-getty.(*session).handleTCPPackage
        /Users/phil/go/pkg/mod/github.com/apache/dubbo-getty@v1.4.5/session.go:627
github.com/apache/dubbo-getty.(*session).handlePackage
        /Users/phil/go/pkg/mod/github.com/apache/dubbo-getty@v1.4.5/session.go:549

Client dubbogo.yml

dubbo:
  consumer:
    references:
      UserProvider:
#        protocol: jsonrpc
        protocol: dubbo
        interface: com.ikurento.user.UserProvider

What you expected to happen:
Server正常处理请求

How to reproduce it (as minimally and precisely as possible):

Anything else we need to know?:

[PhilYue]

@PhilYue

[PhilYue]

dubbo-go/protocol/dubbo/impl/hessian.go#unmarshalRequestBody

        attachments, err := decoder.Decode()
	if err != nil {
		return perrors.WithStack(err)
	}

	//if attachments == nil {
	if attachments == nil || attachments == "" { // || attachments == ""
		attachments = map[interface{}]interface{}{constant.InterfaceKey: target}
	}

	if v, ok := attachments.(map[interface{}]interface{}); ok {
		v[DUBBO_VERSION_KEY] = dubboVersion
		req[6] = ToMapStringInterface(v)
		buildServerSidePackageBody(p)
		return nil
	}
	return perrors.Errorf("get wrong attachments: %+v", attachments)

[AlexStocks]

try to fix it by yourself?