AIDL Interfaces
You declare the API of your service using an AIDL interface:
birthday_service/aidl/com/example/birthdayservice/IBirthdayService.aidl:
package com.example.birthdayservice;
/** Birthday service interface. */
interface IBirthdayService {
    /** Generate a Happy Birthday message. */
    String wishHappyBirthday(String name, int years);
}
birthday_service/aidl/Android.bp:
aidl_interface {
    name: "com.example.birthdayservice",
    srcs: ["com/example/birthdayservice/*.aidl"],
    unstable: true,
    backend: {
        rust: { // Rust is not enabled by default
            enabled: true,
        },
    },
}
Add vendor_available: true if your AIDL file is used by a binary in the vendor
partition.