Datagram codec for UdpFramed to extract JSON playload from incoming UDP datagrams

beaconcodec.rs

struct BeaconCodec;

impl Decoder for BeaconCodec {
    // To keep decoded packets flowing, even malformed packets need to be handled, therefore we use
    // None to signal a datagram that possibly does not belong to the protocol.
    type Item = Option<BeaconPacket>;
    type Error = io::Error;

    fn decode(&mut self, buf: &mut BytesMut) -> Result<Option<Self::Item>, Self::Error> {
        if buf.is_empty() {
            // If an empty datagram were received, we signal that more data is needed.
            Ok(None)
        } else {
            // Here we assume that a single UDP datagram will be passed to decode() as a whole
            // If we cannot parse it into a valid JSON BeaconPacket, we assume that it is not a
            // half packet, but belongs to a different protocol.
            let packet = serde_json::from_slice(buf).map(Some).unwrap_or(None);
            // According to the docs, it is our responsibility to drop used bytes from the buffer
            buf.clear();
            // We never return an Err as it would close the socket, but we would like to listen
            // for more BeaconPackets even if a malformed one is received.
            Ok(Some(packet))
        }
    }
}