proto2 extensions

[oxyii]

As we know, Proto3 does not support extensions (except for declaring custom options). Extensions are fully supported in proto2 and editions though (link).

For common tasks (such a CRUD) we can create the following definition:

syntax = "proto2"; // proto2 !!!

package proto;

import "google/protobuf/timestamp.proto";

// common model

message Model {
  optional string id = 1001;
  optional string version = 1002;

  optional google.protobuf.Timestamp created_at = 10001;
  optional google.protobuf.Timestamp updated_at = 10002;
  optional google.protobuf.Timestamp deleted_at = 10003;

  extensions 100000 to 999999; // mount points for extensions
}

// define messages

message Person {
  required string first_name = 1;
  required string last_name = 2;
}

// mount messages to common model

extend Model {
  optional Person person = 100001;
}

After executing protoc for Golang (protoc-gen-go), I see that the following construction was created for Golang:

var file_experimant_proto_extTypes = []protoimpl.ExtensionInfo{
    {
        ExtendedType:  (*Model)(nil),
        ExtensionType: (*Person)(nil),
        Field:         100001,
        Name:          "proto.person",
        Tag:           "bytes,100001,opt,name=person",
        Filename:      "experimant.proto",
    },
}

// Extension fields to Model.
var (
    // optional proto.Person person = 100001;
    E_Person = &file_experimant_proto_extTypes[0]
)

So, I can register extensions on client-side then extract it on server-side, or vise versa:

import "google.golang.org/protobuf/proto"

// SET EXTENSION

id := "123"
m := &Model{Id: &id}

fn := "First"
ln := "Name"
p := &Person{FirstName: &fn, LastName: &ln}

proto.SetExtension(m, E_Person, p)

// GET EXTENSION

person := proto.GetExtension(m, E_Person)
// or
proto.RangeExtensions(m, func(t protoreflect.ExtensionType, value any) bool {
    if t.TypeDescriptor().FullName() == E_Person.TypeDescriptor().FullName() {
        person := value.(*Person)
    }
    return true
})

---

protoc-gen-ts does not generate (and does not registered them in Model class) an object(s) of classes ExtensionFieldInfo and ExtensionFieldBinaryInfo that is equivalent to Golang's protoimpl.ExtensionInfo.

In addition, as I can see from generated code, model serializer will still ignore extension fields even if I bind it manually, because the generated code explicitly loops through known fields, without knowing anything about extensions.

[oxyii]

I tried ts-protoc-gen and it works correctly. Model has extensions and extensionsBinary props and model serializer/deserializer calls serializeBinaryExtensions and readBinaryExtension functions