ng_gateway_driver/
macros.rs

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#[macro_export]
macro_rules! driver_metadata {
    ($metadata:expr) => {
        use prost::Message;
        use std::sync::Mutex;

        static METADATA_BUFFER: Mutex<Option<Vec<u8>>> = Mutex::new(None);

        #[no_mangle]
        pub extern "C" fn metadata() -> *const u8 {
            let metadata = $metadata;
            let mut buf = Vec::new();
            metadata
                .encode(&mut buf)
                .expect("Failed to encode Protobuf");
            let ptr = buf.as_ptr();
            *METADATA_BUFFER.lock().unwrap() = Some(buf);
            ptr
        }

        #[no_mangle]
        pub extern "C" fn metadata_length() -> usize {
            METADATA_BUFFER
                .lock()
                .unwrap()
                .as_ref()
                .map_or(0, |buf| buf.len())
        }

        #[no_mangle]
        pub extern "C" fn free_metadata() {
            *METADATA_BUFFER.lock().unwrap() = None;
        }
    };
}