Nullable WellKnownTypes - Timestamp and Duration

[zs-dima]

google accounts Timestamp and Duration (WellKnownTypes) as nullable types, but grpc-dart library account them as non-nullable types.

How I could pass null for the Timestamp or Duration WellKnownTypes in this case without adding own types ?

Could be nice to make this type nullable.

https://github.com/protocolbuffers/protobuf/issues/2168

Thanks in advance

[mraleph]

Sorry, I don't understand the question. Could you provide some code to illustrate what you are asking?

From Dart language perspective (post NNBD) a type like Duration can't be nullable. If you want to store null it has to be Duration?.

From protobuf perspective - there is no concept of nullable Duration either AFAIK.

[zs-dima]

@mraleph thanks for reply

For the protobuf and other languages proto google.protobuf.Duration means Duration? in dart. But it is Duration currently - so I could not pass Null as Duration or Timestamp to the backend or etc

Could be nice to make google.protobuf.Duration as Duration? in dart and make google.protobuf.Timestamp as DateTime? in dart

[zs-dima]

@mraleph I send you protobuf protocol discussion where google.protobuf.Timestamp mentioned as nulluble type. so google.protobuf.Timestamp have to be DateTime? in dart

however protobuf protocol does not have non-nulluble alternatives for this types (same as int32<>Int32Value, string<>StringValue and etc) but it is question to the protobuf protocol.

[mraleph]

I looked a bit into this. It seems that C# protobuf implementation has a really different behavior from how other protobuf implementations behave. Most specifically in C# you can actually have null stored in a field even though you are not supposed to be able to distinguish between missing fields and fields initialized with default values. Given a message:

message Msg {
    google.protobuf.Timestamp update = 1;
}

C# protoc backend generates:

  private global::Google.Protobuf.WellKnownTypes.Timestamp update_;
  public global::Google.Protobuf.WellKnownTypes.Timestamp Update {
    get { return update_; }
    set {
      update_ = value;
    }
  }

While Java backend generates:

    private com.google.protobuf.Timestamp update_;
    /**
     * <code>.google.protobuf.Timestamp update = 1;</code>
     * @return Whether the update field is set.
     */
    @java.lang.Override
    public boolean hasUpdate() {
      return update_ != null;
    }
    /**
     * <code>.google.protobuf.Timestamp update = 1;</code>
     * @return The update.
     */
    @java.lang.Override
    public com.google.protobuf.Timestamp getUpdate() {
      return update_ == null ? com.google.protobuf.Timestamp.getDefaultInstance() : update_;
    }

Java seems to match behavior prescribed by wire format, but C# seems to expose whether field is present or absent through nullability. It is not specific to Timestamp in anyway - just a generic behaviour for all fields.

If you want to mimic C# behaviour (e.g. if you are communicating with C# server which is misusing protobufs due to, what I think is essentially a bug in original C# protoc implementation) you have to manually clear the field, e.g. for a Msg class generated from protobuf above you could add an extension:

extension NullableTimestamp on Msg {
  void set UpdateOrNull(DateTime? value) {
    if (value != null) {
      Update = Timestamp.fromDateTime(value);
    } else {
      clearUpdate();
    }
  }

  DateTime? get UpdateOrNull => hasUpdate() ? update.toDateTime() : null;
}

Unfortunately you will have to write these extensions manually.

[zs-dima]

@mraleph thanks a lot for the workaround at least. I agree that it is protobuf protocol issue and it have to be Timestamp <> TimestampValue and Duration <> DurationValue same as other nullable types.

[zs-dima]

@mraleph I created related protobuf protocol issue about https://github.com/protocolbuffers/protobuf/issues/8822