What is it

Structure or classes used to represent data being transferred between different parts of a system or between systems

Illustration

Protofile definition for a user creation process in a system

// User DTO
message User {
  int32 user_id = 1;
  string name = 2;
  repeated string addresses = 3;
  bool is_active = 4;
  UserType user_type = 5;
}

// UserType enum which is used in user DTO
enum UserType {
  REGULAR = 0;
  PREMIUM = 1;
}

// Service definition that accepts a user DTO and returns a user DTO
service UserService {
  rpc createUser(User) returns (User);
}

In above, we have User DTO, which is used to create a user using the createUser method of UserService

• When a protoc compiler reads this proto file, it will create:
  • a DTO class named User
  • a service class named UserService
  • an enum UserType