Defining custom options

ScalaPB allows you to define custom options you can use to annotate any element in a proto file, and access these annotations at run time.

Learn more about custom options.

Define your options#

In my_opts.proto:

syntax = "proto2";
package custom_options;
import "google/protobuf/descriptor.proto";
extend google.protobuf.FileOptions {
optional string my_file_option = 50000;
message MyMessageOption {
optional int32 priority = 1;
extend google.protobuf.MessageOptions {
optional MyMessageOption my_message_option = 50001;
message Tag {
optional string name = 1;
// Extensions can be defined inside messages,
// But there is no relationship between the enclosing message and the
// extension - it only uses for namespace purposes.
message Wrapper {
extend google.protobuf.FieldOptions {
repeated Tag tags = 50003;

Use the options like this:

syntax = "proto2";
package custom_options;
import "custom_options/my_opts.proto";
option (my_file_option) = "hello!";
message OneMessage {
option (my_message_option).priority = 17;
// Field level option, with repeated field.
optional int32 number = 1 [(Wrapper.tags) = {name: "tag1"},
(Wrapper.tags) = {name: "tag2"}];

Extensions that are defined at file scope are generated under the descriptor proto (usually name FileNameProto). Otherwise, the extension is defined in the companion object of the containing class.

To access the option value of an element, you need to obtain its descriptor:

use_opts.CustomOptionsUseOptsProto.scalaDescriptor.getOptions) ==
use_opts.OneMessage.scalaDescriptor.getOptions).get ==
my_opts.MyMessageOption().update(_.priority := 17))
val numberField = use_opts.OneMessage.descriptor.findFieldByName(
numberField.getOptions) == Seq(
my_opts.Tag(name = Some("tag1")),
my_opts.Tag(name = Some("tag2"))))

If you prefer to start with the descriptor, you use can the extension method:

my_opts.CustomOptionsMyOptsProto.myFileOption) == Some("hello!"))
my_opts.CustomOptionsMyOptsProto.myMessageOption).get ==
my_opts.MyMessageOption().update(_.priority := 17))
my_opts.Wrapper.tags) == Seq(
my_opts.Tag(name = Some("tag1")),
my_opts.Tag(name = Some("tag2"))))

Example code#

The full source code of this example is available below: