I'm working on a tutorial about gRPC. When I generated the .pb.go
file, I'm getting some XXX_*
type in my struct.
This is my consignment.proto
file:
syntax = "proto3";
package go.micro.srv.consignment;
service ShippingService {
rpc CreateConsignment(Consignment) returns (Response) {}
}
message Consignment {
string id = 1;
string description = 2;
int32 weight = 3;
repeated Container containers = 4;
string vessel_id = 5;
}
message Container {
string id = 1;
string customer_id = 2;
string origin = 3;
string user_id = 4;
}
message Response {
bool created = 1;
Consignment consignment = 2;
}
This is the struct in the .pb.go
file. Can someone tell me why are there 3 XXX
types in my struct
? Shouldn't the struct be reflecting what I'm defining in my proto
?
type Consignment struct {
Id string `protobuf:"bytes,1,opt,name=id" json:"id,omitempty"`
Description string `protobuf:"bytes,2,opt,name=description" json:"description,omitempty"`
Weight int32 `protobuf:"varint,3,opt,name=weight" json:"weight,omitempty"`
Containers []*Container `protobuf:"bytes,4,rep,name=containers" json:"containers,omitempty"`
VesselId string `protobuf:"bytes,5,opt,name=vessel_id,json=vesselId" json:"vessel_id,omitempty"`
XXX_NoUnkeyedLiteral struct{} `json:"-"`
XXX_unrecognized []byte `json:"-"`
XXX_sizecache int32 `json:"-"`
}
A . proto file is similar to a JSON file in that it represents structured data, but you can run a compiler on the . proto file to generate code that can read and write the data in the programming language of your choice. For more information about protocol buffers, see Protocol Buffer Developer Guide on Google's site.
The compiler plugin, protoc-gen-go, will be installed in $GOBIN, defaulting to $GOPATH/bin. It must be in your $PATH for the protocol compiler, protoc, to find it.
Protobuf has an option for marking a “field” as deprecated. optional int32 old_field = 6 [deprecated=true]; Full snipped from their documentation: deprecated (field option): If set to true , indicates that the field is deprecated and should not be used by new code.
The XXX_
types are used by the Protobuf library to store unknown fields. When you decode a proto, there may be additional fields in the serialized data that the library doesn't know what to do with. This can happen, for instance, when the reader and writer of the data are using different copies of the proto file. This is a feature to help with backwards compatibility between clients and serves built at different times.
Additionally, the XXX fields allow you to expose extensions, which were part of Proto2. They were removed in Proto3 in favor of Any, but the library still needs to support them.
As for what you should do with these? I would just leave them alone, and don't reference them. You don't need to set them, and you don't need to read them. The Go protobuf library will handle them for you.
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