Out-of-the-box types

On top of all the scalar types that Protobuf provides as part of the language, it also provides some already-defined types called well-known types (WKTs). All these types can be found in the src/google/protobuf folder in the GitHub repository (https://github.com/protocolbuffers/protobuf/tree/main/src/google/protobuf), and they are all defined under the google.protobuf package.

Here is a list of the most common WKTs available:

• Duration
• Timestamp
• FieldMask
• Any
• Struct

Let’s go through all of these types and see what they are used for.

Duration and timestamp

These two types are pretty interesting because they show us the importance of naming, documenting with comments, and separating definitions into different files for reusability. In fact, these two types have the same definitions except for the message name. Here are the diff command results between those two (simplified):

-message Timestamp {
-  // Represents...