wireshark/test/protobuf_lang_files/user_defined_types/test_map.proto

syntax="proto3";

package test.map;

message Foo {
  int32 param1 = 1;
}

message MapMaster {
  oneof Abc {
    string param2 = 2;
    string param3 = 3;
  }

  map<string, int64> param4 = 4;
  map<sint32, Foo> param5 = 5;
}