Function read_frames 

pub async fn read_frames<R: AsyncRead + Unpin>(
    reader: R,
    frames: Sender<Result<Vec<u8>>>,
)

Read whole RADIUS packets from a stream: the 4-byte header’s Length says how much follows. A length outside 20..=4096 ends the connection (RFC 6614 §2.5: the stream cannot be resynchronised), as does EOF.