Handling Unknown Enum Values

[FutureSeller]

Greetings!

In enumToJsonInternal function, it appears that when an unknown value is encountered, the integer value is passed through as is.

function enumToJsonInternal(
  desc: DescEnum,
  value: unknown,
  enumAsInteger: boolean,
): string | number | null {
  if (typeof value != "number") {
    throw new Error(
      `cannot encode ${desc} to JSON: expected number, got ${formatVal(value)}`,
    );
  }
  if (desc.typeName == "google.protobuf.NullValue") {
    return null;
  }
  if (enumAsInteger) {
    return value; // << [[ here ]]
  }
  const val = desc.value[value] as DescEnumValue | undefined;
  return val?.name ?? value; // if we don't know the enum value, just return the number << [[ here ]]
}

According to protobuf buffers document, the default value for an enum can be used 0. How about adding an option to specify a default value for unknown enum values, or converting them to 0?

Thanks!

[timostamm]

Hey Jihoon,

in proto3, enums are open, which means you can assign values that are not defined in the enum.

For example:

syntax="proto3";

enum Foo {
  FOO_UNSPECIFIED = 0;
  FOO_A = 1;
}

message Example {
  Foo foo = 1;
}

Creating an instance of the message Example, and assigning the value 2 to the field foo is not an error. Serializing the message to JSON should yield {"foo": 2}, and parsing this JSON should yield a message with foo = 2.

This can be unexpected, but we cannot change this behavior because it would not be compatible with other Protobuf implementations.