Protobuf无法识别相同的软件包

Question

I have some code that uses google protobuf. These are the source files:

Proto file:

syntax = "proto3";

package my_package.protocol;
option go_package = "protocol";

import "github.com/golang/protobuf/ptypes/empty/empty.proto";

...

service MyService {
    rpc Flush        (google.protobuf.Empty) returns (google.protobuf.Empty);
}

Compiled go file:

package protocol

import proto "github.com/golang/protobuf/proto"
import fmt "fmt"
import math "math"
import google_protobuf "github.com/golang/protobuf/ptypes/empty"

import (
    context "golang.org/x/net/context"
    grpc "google.golang.org/grpc"
)

...

type MyServiceClient interface {
    Flush(ctx context.Context, in *google_protobuf.Empty, opts ...grpc.CallOption) (*google_protobuf.Empty, error)
}

And when I finally try to use the compiled service like this:

import (
    "golang.org/x/net/context"

    pb "myproject/protocol"

    google_protobuf "github.com/golang/protobuf/ptypes/empty"
)
...
func Flush(sink pb.MyServiceClient) {
    _, err = sink.Flush(context.Background(), *google_protobuf.Empty{})
    ...
}

I get the following error:

Cannot use '*google_protobuf.Empty{}' (type "myproject/vendor/github.com/golang/protobuf/ptypes/empty".Empty) as type "myproject/vendor/github.com/golang/protobuf/ptypes/empty".*google_protobuf.Empty

Which are the same thing (they even resolve to the same file). What am I missing here?

Answer 1

Your error is on this line:

 _, err = sink.Flush(context.Background(), *google_protobuf.Empty{})

*google_protobuf.Empty{} is attempting to dereference the struct, but your function prototype expects a pointer to a google_protobuf.Empty. Use &google_protobuf.Empty{} instead. And when you end up with a real data structure rather than empty, you will probably do something along the lines of:

  req := google_protobuf.MyRequestStruct{}
  _, err = service.Method(context.Background(), &req)

For an overview of pointer syntax in go, please take the tour