Help regarding Protoreflect

[Aniket_Pathak]

I have a gRPC service which takes Request and Response with specific formats.

message Response {
     string ID = 1;
     ScorerA ScrA = 2;
     ScorerB ScrB = 3;
}
// Any one of ScorerA and ScorerB needs to populated in Response and will be decided at runtime

message ScorerA {
    string Name = 1;
}

message ScorerB {
    string Section = 1;
}

I have created map of Scorer Name to Scorer Type:

var scrA *pb.ScorerA = &pb.ScorerA{}
var scrAType protoreflect.MessageType = scrA.ProtoReflect().Type()

var scrB *pb.ScorerB = &pb.ScorerB{}
var scrBType protoreflect.MessageType = scrB.ProtoReflect().Type()

ScorerTypes := map[string]protoreflect.MessageType {
     "ScorerA":  scrAType
     "ScorerB":  scrBType
}

In my gRPC server I am getting the Scorer Name at runtime based on some condition.

scorerName := "ScorerA" // Let's say

Now I create an empty structure (not to be confused with go struct) of type scrAType and set values for fields:

var recType protoreflect.MessageType = ScorerTypes[scorerName]
var rec protoreflect.Message = recType.New()
.
.
.
rec.Set(_, _) // Setting values for fields

Finally converted to protoreflect.ProtoMessage using:

var finalScorer protoreflect.ProtoMessage = rec.Interface()

Reference: https://pkg.go.dev/google.golang.org/protobuf/reflect/protoreflect#hdr-Go_Type_Descriptors

Now my gRPC server has return type of *pb.Response, So:

resp := &pb.Response{ID: "1", ScrA: finalScorer}

This gives the following error:

cannot use finalScorer (variable of type protoreflect.ProtoMessage) as *"proto".ScorerA value in struct literal

How can I convert protoreflect.ProtoMessage to actual pb (lets say pb.ScorerA)?
If there’s any better way to handle this usecase please let me know.

[apmattil (Ari Mattila)]

could the problem be that you are initializing nested struct.

Nested Structure in Golang - GeeksforGeeks

without compiling, could this work:

resp := &pb.Response{ID: "1", ScrA:ScorerA{finalScorer}}

if not, try to set the resp fields outside of initialization.

[chengjiexu]

@Aniket_Pathak

finalScorer

rsp := &pb.Response{ID: "1"}

rspMsg := rsp.ProtoReflect()
rspType := rspMsg.Type()
rspFields := rspType.Descriptor().Fields()

rv := protoreflect.ValueOf(rsp.ProtoReflect())
rv.Message().Set(rspFields.ByTextName("ScrA"), protoreflect.ValueOf(finalScorer.ProtoReflect()))