fn decode()

in neqo-transport/src/tparams.rs [277:340]
64 lines of code
8 McCabe index (conditional complexity)

    fn decode(dec: &mut Decoder) -> Res<Option<(TransportParameterId, Self)>> {
        let tp = dec.decode_varint().ok_or(Error::NoMoreData)?;
        let content = dec.decode_vvec().ok_or(Error::NoMoreData)?;
        qtrace!("TP {tp:x} length {:x}", content.len());
        let tp = match tp.try_into() {
            Ok(tp) => tp,
            Err(Error::UnknownTransportParameter) => return Ok(None), // Skip
            Err(e) => return Err(e),
        };
        let mut d = Decoder::from(content);
        let value = match tp {
            OriginalDestinationConnectionId
            | InitialSourceConnectionId
            | RetrySourceConnectionId => Self::Bytes(d.decode_remainder().to_vec()),
            StatelessResetToken => {
                if d.remaining() != 16 {
                    return Err(Error::TransportParameterError);
                }
                Self::Bytes(d.decode_remainder().to_vec())
            }
            IdleTimeout
            | InitialMaxData
            | InitialMaxStreamDataBidiLocal
            | InitialMaxStreamDataBidiRemote
            | InitialMaxStreamDataUni
            | MaxAckDelay
            | MaxDatagramFrameSize => match d.decode_varint() {
                Some(v) => Self::Integer(v),
                None => return Err(Error::TransportParameterError),
            },
            InitialMaxStreamsBidi | InitialMaxStreamsUni => match d.decode_varint() {
                Some(v) if v <= (1 << 60) => Self::Integer(v),
                _ => return Err(Error::StreamLimitError),
            },
            MaxUdpPayloadSize => match d.decode_varint() {
                Some(v) if v >= MIN_INITIAL_PACKET_SIZE.try_into()? => Self::Integer(v),
                _ => return Err(Error::TransportParameterError),
            },
            AckDelayExponent => match d.decode_varint() {
                Some(v) if v <= 20 => Self::Integer(v),
                _ => return Err(Error::TransportParameterError),
            },
            ActiveConnectionIdLimit => match d.decode_varint() {
                Some(v) if v >= 2 => Self::Integer(v),
                _ => return Err(Error::TransportParameterError),
            },
            DisableMigration | GreaseQuicBit => Self::Empty,
            TransportParameterId::PreferredAddress => Self::decode_preferred_address(&mut d)?,
            MinAckDelay => match d.decode_varint() {
                Some(v) if v < (1 << 24) => Self::Integer(v),
                _ => return Err(Error::TransportParameterError),
            },
            VersionInformation => Self::decode_versions(&mut d)?,
            #[cfg(test)]
            TransportParameterId::TestTransportParameter => {
                Self::Bytes(d.decode_remainder().to_vec())
            }
        };
        if d.remaining() > 0 {
            return Err(Error::TooMuchData);
        }
        qtrace!("TP decoded; type {tp} val {value:?}");
        Ok(Some((tp, value)))
    }