Behavior compatibility

If you follow the practice of only adding things, maintaining ABI/API compatibility and wire compatibility is fairly straightforward. However, this alone isn’t sufficient to ensure your existing client’s expected behavior is maintained.

There are a number of things you need to be aware of to ensure that the behavior of your service doesn’t change when you add new fields for example. Let’s take a look at a few common scenarios.

Default values for new fields

Any new fields added to protobuf messages will be given a default value that’s specific to the type. For example, a new int32 field will have a value of 0, a string will have "", and a message field will be nil (or the language equivalent).

For a full list of the default values for each field type, see the protobuf docs at https://developers.google.com/protocol-buffers/docs/proto3#default.

This is the standard behavior for proto3. Working against the protocol can...