d a type for each field in the message. Here is the <code>.proto</code> file that defines your messages, <code>addressbook.proto</code>:</p>
<pre><code class="proto">syntax = "proto2";

package tutorial;

option java_package = "protobuf.examples.tutorial";
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 {
    require