fn decode()

in neqo-http3/src/frames/hframe.rs [171:226]
56 lines of code
5 McCabe index (conditional complexity)

    fn decode(frame_type: HFrameType, frame_len: u64, data: Option<&[u8]>) -> Res<Option<Self>> {
        if frame_type == H3_FRAME_TYPE_DATA {
            Ok(Some(Self::Data { len: frame_len }))
        } else if let Some(payload) = data {
            let mut dec = Decoder::from(payload);
            Ok(match frame_type {
                H3_FRAME_TYPE_DATA => unreachable!("DATA frame has been handled already"),
                H3_FRAME_TYPE_HEADERS => Some(Self::Headers {
                    header_block: dec.decode_remainder().to_vec(),
                }),
                H3_FRAME_TYPE_CANCEL_PUSH => Some(Self::CancelPush {
                    push_id: dec.decode_varint().ok_or(Error::HttpFrame)?.into(),
                }),
                H3_FRAME_TYPE_SETTINGS => {
                    let mut settings = HSettings::default();
                    settings.decode_frame_contents(&mut dec).map_err(|e| {
                        if e == Error::HttpSettings {
                            e
                        } else {
                            Error::HttpFrame
                        }
                    })?;
                    Some(Self::Settings { settings })
                }
                H3_FRAME_TYPE_PUSH_PROMISE => Some(Self::PushPromise {
                    push_id: dec.decode_varint().ok_or(Error::HttpFrame)?.into(),
                    header_block: dec.decode_remainder().to_vec(),
                }),
                H3_FRAME_TYPE_GOAWAY => Some(Self::Goaway {
                    stream_id: StreamId::new(dec.decode_varint().ok_or(Error::HttpFrame)?),
                }),
                H3_FRAME_TYPE_MAX_PUSH_ID => Some(Self::MaxPushId {
                    push_id: dec.decode_varint().ok_or(Error::HttpFrame)?.into(),
                }),
                H3_FRAME_TYPE_PRIORITY_UPDATE_REQUEST | H3_FRAME_TYPE_PRIORITY_UPDATE_PUSH => {
                    let element_id = dec.decode_varint().ok_or(Error::HttpFrame)?;
                    let priority = dec.decode_remainder();
                    let priority = Priority::from_bytes(priority)?;
                    if frame_type == H3_FRAME_TYPE_PRIORITY_UPDATE_REQUEST {
                        Some(Self::PriorityUpdateRequest {
                            element_id,
                            priority,
                        })
                    } else {
                        Some(Self::PriorityUpdatePush {
                            element_id,
                            priority,
                        })
                    }
                }
                _ => None,
            })
        } else {
            Ok(None)
        }
    }