Creating protobuf messages

In this section, we will learn how to create protobuf messages. We will introduce the concepts of protobuf messages and how to define them in a proto file.

gRPC is a contract-first framework, meaning that the gRPC service and messages must be defined in a proto file. When we talk about messages, we are talking about the data that is sent between the client and the server. While gRPC messages may be similar to the data model in RESTful APIs, they are not the same. RESTful APIs are centered around resources, and the data model is usually a resource model that can be mapped to one or multiple database tables. In contrast, gRPC is action-based, and the message can be any other type of data model or other message sent between the client and the server. Therefore, gRPC messages may not be exactly mapped to a resource model in RESTful APIs.

For example, when creating an invoice through a RESTful API using JSON as the data format, we need to send an HTTP POST...