If you want to use protocol buffers to generate dart-code you need to install the dart-protoc-plugin

pub global activate protoc_plugin

Default proto-files are located (Linux) in

/usr/local/google/protobuf

To generate dart-code for this proto file:

syntax = "proto3";
package tutorial;

import "google/protobuf/timestamp.proto";

message Person {
  string name = 1;
  int32 id = 2;  // Unique ID number for this person.
  string email = 3;

  enum PhoneType {
    MOBILE = 0;
    HOME = 1;
    WORK = 2;
  }

  message PhoneNumber {
    string number = 1;
    PhoneType type = 2;
  }

  repeated PhoneNumber phones = 4;

  google.protobuf.Timestamp last_updated = 5;
}

// Our address book file is just one of these.
message AddressBook {
  repeated Person people = 1;
}
protoc --dart_out=. ./test.proto