How to support patch rest request with protobuf 3

Question

We often have use cases where we only want to update a subset fields on a resource. So if we have a resource Person:

type Person struct {
    Age int
    Name string
    Otherfield string
}

Say the calling client only wants to update the Age field. How would an endpoint be normally set up to handle this?

I believe this should be done with a PATCH request, with only the fields being set as part of the payload, ie:

{
    Age: 21
}

However, this won't work with proto3 because as far as I know there are no null fields, only default values. This won't work in many cases where the default value is valid.

Answer 1

Looking at Google own protobuf files (e.g. here), they use FieldMask for partial update.

FieldMask object is passed along with the request, and has the form (in JSON):

{
   mask: "Person.Age"
}

This allows the client to tell the server which fields they wish to update, without counting on the partial message itself to figure this out.

I think this adds unnecessary complexity on (each!) client, but we couldn't find any other way to achieve partial updates with proto3.

You can see full documentation of FieldMask here.

Note that it can also be used to filter out responses if the client doesn't need the entire object.