toukii.github.io

protobuf descriptor

Descriptor

go-grpc官方的Descriptor定义在 github.com/golang/protobuf/protoc-gen-go/descriptor/descriptor.pb.go中。 已第三方gogo为例，代码见：https://github.com/gogo/protobuf/blob/master/protoc-gen-gogo/descriptor/descriptor.pb.go

Descriptor有以下一些类型，从它的名称可以看出是描述什么的，也可以参考之前的文章prodobuf-descriptor：

FileDescriptorProto 文件描述
ServiceDescriptorProto 服务描述
MethodDescriptorProto 方法描述
DescriptorProto message描述
FieldDescriptorProto 字段描述
OneofDescriptorProto
EnumDescriptorProto
EnumValueDescriptorProto

Descriptor的关系：

type FileDescriptorProto struct {
	MessageType []*DescriptorProto
	EnumType    []*EnumDescriptorProto
	Service     []*ServiceDescriptorProto
	Extension   []*FieldDescriptorProto
	Options     *FileOptions
}

type ServiceDescriptorProto struct {
	Method               []*MethodDescriptorProto
	Options              *ServiceOptions
}

type MethodDescriptorProto struct {
	Options    *MethodOptions
}

FileDescriptorProto包含了若干ServiceDescriptorProto，ServiceDescriptorProto又包含了若干MethodDescriptorProto。message的定义放在FileDescriptorProto中。 几个Options是扩展用的，参考protobuf-option。 FieldDescriptorProto可能依赖其他FileDescriptorProto的FieldDescriptorProto，如果要得到完整的Descriptor，需要收集依赖的FieldDescriptorProto, 即 其他proto的FileDescriptorProto, 最终得到一个FileDescriptorSet：

type FileDescriptorSet struct {
	File                 []*FileDescriptorProto
}

fileDescriptor

生成grpc代码后，在pb.go文件中可以拿到 FileDescriptorProto，这个FileDescriptorProto只描述了当前proto文件的Descriptor。

var fileDescriptorCharts = []byte{
	// 140 bytes of a gzipped FileDescriptorProto
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}

在decode set时（grpcurl.DescriptorSourceFromFileDescriptorSet(p.fileDescriptorSet)），可能会因为缺少依赖报错，如：no descriptor found for "common.proto"，这需要将缺少的依赖加进来。最终可以得到完整的FileDescriptorSet。

desc

desc -m helloworld.Greeter/SayHello helloworld extension google.protobuf

收集helloworld.Greeter/SayHello的依赖, 收集成功后，可以收集一份完整的helloworld.Greeter fileDescriptorSet。 收集目录：helloworld extension google.protobuf

日志如下：

imports: [helloworld extension google.protobuf]
INFO[0000] collect 3 pb.go
extension/extension.pb.go
helloworld/lang.pb.go
helloworld/greeter.pb.go
DEBU[0000] search helloworld.Greeter/SayHello, pkg: helloworld, service: helloworld.Greeter
DEBU[0000] searching helloworld/greeter.pb.go
INFO[0000] helloworld.Greeter/SayHello --> /Users/toukii/PATH/GOPATH/ezbuy/goflow/src/github.com/tgrpc/ngrpc/helloworld/greeter.pb.go
DEBU[0000] no descriptor found for "extension/extension.proto" ==> extension/extension.proto extension/extension.pb.go
DEBU[0000] searching extension/extension.pb.go
INFO[0000] extension/extension.proto --> /Users/toukii/PATH/GOPATH/ezbuy/goflow/src/github.com/tgrpc/ngrpc/extension/extension.pb.go
DEBU[0000] searching extension/extension.pb.go
INFO[0000] extension/extension.proto --> /Users/toukii/PATH/GOPATH/ezbuy/goflow/src/github.com/tgrpc/ngrpc/extension/github.com/tgrpc/ngrpc/extension/extension.pb.go
WARN[0000] extension/extension.pb.go is duplicated
DEBU[0000] no descriptor found for "google.protobuf/descriptor.proto" ==> google.protobuf/descriptor.proto google.protobuf/descriptor.pb.go
extension/extension.pb.go google.protobuf/descriptor.pb.go
helloworld/lang.pb.go google.protobuf/descriptor.pb.go
helloworld/greeter.pb.go google.protobuf/descriptor.pb.go
WARN[0000] not found pb for:helloworld.Greeter/SayHello
data writing ==> helloworld.Greeter.desc