unlabeled_field_get_packed_size() function
Calculate the serialized size of a single unlabeled message field, including the space needed by the preceding tag. Returns 0 if the field isn't set or if it is set to a "zeroish" value (null pointer or 0 for numerical values). Unlabeled fields are supported only in proto3.
Arguments
field
Field descriptor for member.
Return value
Number of bytes required.