Is Grpc's request can return different responses for some conditions

July 28, 2023

service Greeter {
  rpc OpenChannel(RequestOpenChannel) returns (stream ResponseOpenChannel);}

message RequestOpenChannel{
    int32 task_id =1;
}

message ResponseOpenChannel {
     int32 response_id =1;
}

This is my ProtoFile. My TaskID like (1 = ConditionOne, 2 = ConditionTwo).

I want to send response from server to the client after looking some condition.

service Greeter {
  rpc OpenChannel(RequestOpenChannel) returns (stream ResponseOpenChannel , ResponseOpenChannel2);}
message ResponseOpenChannel2 {
     int32 response_id =1;
}

And that is my expected server code.

if(request.TaskID == 1){ ResponseOpenChannel1 response = some stuff }

else if(request.TaskID == 2){ ResponseOpenChannel2 response = some stuff }

>Solution :

This sounds like a job for oneof; if you’re using contract-first .proto, then you’d have something like:

message ResponseOpenChannel {
    int32 response_id =1;
    oneof response {
        Foo foo = 2;
        Bar bar = 3;
    }
}
message Foo { ... }
message Bar { ... }

and you’d return a ResponseOpenChannel with either a foo = new Foo {...} or a bar = new Bar {...}

If you’re using code-first protobuf-net[.Grpc], then this is 100% wire-identical to:

[ProtoContract]
[ProtoInclude(2, typeof(Foo))]
[ProtoInclude(3, typeof(Bar))]
class ResponseOpenChannel
{
    [ProtoMember(1)]
    public int ResponseId {get;set;}
}
[ProtoContract]
public class Foo : ResponseOpenChannel
{...}
[ProtoContract]
public class Bar : ResponseOpenChannel
{...}

and you would return a new Foo {...} or a new Bar {...}.