sample.proto https://medium.com/@mohsenoid/how-to-setup-your-android-app-to-use-protobuf-96132340de5c

sample.proto

syntax = "proto2";

package tutorial;

option java_package = "com.mohsenoid.protobuftest";
option java_outer_classname = "AddressBookProtos";

message Person {
  required string name = 1;
  required int32 id = 2;
  optional string email = 3;
  
  enum PhoneType {
    MOBILE = 0;
    HOME = 1;
    WORK = 2;
  }
  
  message PhoneNumber {
    required string number = 1;
    optional PhoneType type = 2 [default = HOME];
  }
  
  repeated PhoneNumber phones = 4;
}

message AddressBook {
  repeated Person people = 1;
}