How to return more than one array in Protobuf service rpc

Question

I have the following schema in my .proto file:

service DownloadOctants {
    rpc GetOctants (OctantsQuery) returns (OctantsResponse) {
    }
}

message OctantsQuery {
    repeated int32 octants = 1;
}
message OctantsResponse {
    repeated Mesh meshes = 1;
}
message Mesh {
    repeated float vertices = 1;
    repeated int32 faces = 2;
}

Mesh consists of two arrays. Is that possible?

If no, how else should I design my scheme?

If yes, how do I access the values of the arrays vertices and faces?

I saw the sample program at https://grpc.io/docs/languages/node/basics/ :

var call = client.listFeatures(rectangle);
  call.on('data', function(feature) {
      console.log('Found feature called "' + feature.name + '" at ' +
          feature.location.latitude/COORD_FACTOR + ', ' +
          feature.location.longitude/COORD_FACTOR);
  });

This assumes that listFeatures returns an array, but only one array. It seems to be more challenging to process two or more arrays.

Answer 1

Q1 "Mesh consists of two arrays"

Yes, it's possible as you show in your protobuf.

Q2: "How do I access the value of vertices and faces"

The sample program (Route Guide) ListFeatures method streams responses and so the implementation is different.

Your proto returns OctantsResponse which contains 2 (vertices,faces) arrays so you can:

...
octantsQuery = {
  octants = [1,2,4,5,6]
};

client.getOctants(octantsQuery, (err, octantsResponse) => {
  if (err) {
    console.log(err);
  }

  // Iterate over the Meshes
  octantsResponse.meshes.forEach(m => {
    // Iterate over the vertices
    m.vertices.forEach(v => {
      console.log(`vertex: ${v}`);
    });
    // Iterate over the faces
    m.faces.forEach(f => {
      console.log(`face: ${f}`);
    });
  });
});

It's good practice to include syntax and package definitions in your protos:

syntax = "proto3"; // Or?

package some-namespace;

...