rns-core 0.3.1

use alloc::vec::Vec;
use core::fmt;

use crate::constants;

#[derive(Debug)]
pub enum PacketError {
    TooShort,
    ExceedsMtu,
    MissingTransportId,
    InvalidHeaderType,
    ZeroLengthData,
    /// Hop counts at or above PATHFINDER_M are invalid on received wire packets.
    InvalidHopCount(u8),
}

impl fmt::Display for PacketError {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        match self {
            PacketError::TooShort => write!(f, "Packet too short"),
            PacketError::ExceedsMtu => write!(f, "Packet exceeds MTU"),
            PacketError::MissingTransportId => write!(f, "HEADER_2 requires transport_id"),
            PacketError::InvalidHeaderType => write!(f, "Invalid header type"),
            PacketError::ZeroLengthData => write!(f, "Zero-length data field"),
            PacketError::InvalidHopCount(hops) => write!(f, "Invalid hop count: {}", hops),
        }
    }
}

// =============================================================================
// PacketFlags: packs 5 fields into one byte
// =============================================================================

#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub struct PacketFlags {
    pub header_type: u8,
    pub context_flag: u8,
    pub transport_type: u8,
    pub destination_type: u8,
    pub packet_type: u8,
}

impl PacketFlags {
    /// Pack fields into a single flags byte.
    ///
    /// Bit layout:
    /// ```text
    /// Bit 6:     header_type (1 bit)
    /// Bit 5:     context_flag (1 bit)
    /// Bit 4:     transport_type (1 bit)
    /// Bits 3-2:  destination_type (2 bits)
    /// Bits 1-0:  packet_type (2 bits)
    /// ```
    pub fn pack(&self) -> u8 {
        (self.header_type << 6)
            | (self.context_flag << 5)
            | (self.transport_type << 4)
            | (self.destination_type << 2)
            | self.packet_type
    }

    /// Unpack a flags byte into fields.
    pub fn unpack(byte: u8) -> Self {
        PacketFlags {
            header_type: (byte & 0b01000000) >> 6,
            context_flag: (byte & 0b00100000) >> 5,
            transport_type: (byte & 0b00010000) >> 4,
            destination_type: (byte & 0b00001100) >> 2,
            packet_type: byte & 0b00000011,
        }
    }
}

// =============================================================================
// RawPacket: wire-level packet representation
// =============================================================================

#[derive(Debug, Clone)]
pub struct RawPacket {
    pub flags: PacketFlags,
    pub hops: u8,
    pub transport_id: Option<[u8; 16]>,
    pub destination_hash: [u8; 16],
    pub context: u8,
    pub raw: Vec<u8>,
    pub packet_hash: [u8; 32],
    pub rssi: Option<i16>,
    pub snr: Option<f32>,
}

impl RawPacket {
    /// Offset of the payload in the wire bytes of a packet with this header type.
    #[inline]
    pub const fn data_offset(header_type: u8) -> usize {
        if header_type == constants::HEADER_2 {
            2 + 2 * (constants::TRUNCATED_HASHLENGTH / 8) + 1
        } else {
            2 + constants::TRUNCATED_HASHLENGTH / 8 + 1
        }
    }

    /// The payload: the wire bytes after the header.
    #[inline]
    pub fn data(&self) -> &[u8] {
        &self.raw[Self::data_offset(self.flags.header_type)..]
    }

    /// Pack fields into raw bytes.
    pub fn pack(
        flags: PacketFlags,
        hops: u8,
        destination_hash: &[u8; 16],
        transport_id: Option<&[u8; 16]>,
        context: u8,
        data: &[u8],
    ) -> Result<Self, PacketError> {
        Self::pack_with_max_mtu(
            flags,
            hops,
            destination_hash,
            transport_id,
            context,
            data,
            constants::MTU,
        )
    }

    /// Pack fields into raw bytes and packet hash without constructing a full RawPacket.
    pub fn pack_raw_with_hash(
        flags: PacketFlags,
        hops: u8,
        destination_hash: &[u8; 16],
        transport_id: Option<&[u8; 16]>,
        context: u8,
        data: &[u8],
    ) -> Result<(Vec<u8>, [u8; 32]), PacketError> {
        Self::pack_raw_with_hash_with_max_mtu(
            flags,
            hops,
            destination_hash,
            transport_id,
            context,
            data,
            constants::MTU,
        )
    }

    /// Pack fields into raw bytes with a caller-provided MTU limit.
    pub fn pack_with_max_mtu(
        flags: PacketFlags,
        hops: u8,
        destination_hash: &[u8; 16],
        transport_id: Option<&[u8; 16]>,
        context: u8,
        data: &[u8],
        max_mtu: usize,
    ) -> Result<Self, PacketError> {
        let (raw, packet_hash) = Self::pack_raw_with_hash_with_max_mtu(
            flags,
            hops,
            destination_hash,
            transport_id,
            context,
            data,
            max_mtu,
        )?;

        Ok(RawPacket {
            flags,
            hops,
            transport_id: transport_id.copied(),
            destination_hash: *destination_hash,
            context,
            raw,
            packet_hash,
            rssi: None,
            snr: None,
        })
    }

    /// Pack fields into raw bytes and packet hash with a caller-provided MTU limit.
    pub fn pack_raw_with_hash_with_max_mtu(
        flags: PacketFlags,
        hops: u8,
        destination_hash: &[u8; 16],
        transport_id: Option<&[u8; 16]>,
        context: u8,
        data: &[u8],
        max_mtu: usize,
    ) -> Result<(Vec<u8>, [u8; 32]), PacketError> {
        let raw = Self::pack_raw_with_max_mtu(
            flags,
            hops,
            destination_hash,
            transport_id,
            context,
            data,
            max_mtu,
        )?;
        let packet_hash = Self::compute_packet_hash(flags.header_type, &raw);
        Ok((raw, packet_hash))
    }

    /// Pack only wire bytes when the caller does not need a packet hash.
    /// Validation and encoding match the hash-producing packing methods.
    pub fn pack_raw_with_max_mtu(
        flags: PacketFlags,
        hops: u8,
        destination_hash: &[u8; 16],
        transport_id: Option<&[u8; 16]>,
        context: u8,
        data: &[u8],
        max_mtu: usize,
    ) -> Result<Vec<u8>, PacketError> {
        if flags.header_type == constants::HEADER_2 && transport_id.is_none() {
            return Err(PacketError::MissingTransportId);
        }

        let mut raw = Vec::new();
        raw.push(flags.pack());
        raw.push(hops);

        if let Some(transport_id) = transport_id {
            if flags.header_type == constants::HEADER_2 {
                raw.extend_from_slice(transport_id);
            }
        }

        raw.extend_from_slice(destination_hash);
        raw.push(context);
        raw.extend_from_slice(data);

        if raw.len() > max_mtu {
            return Err(PacketError::ExceedsMtu);
        }

        Ok(raw)
    }

    /// Unpack raw bytes into fields.
    pub fn unpack(raw: &[u8]) -> Result<Self, PacketError> {
        Self::unpack_with::<true, _>(raw)
    }

    /// Unpack wire bytes the caller owns, keeping them as `raw` instead of
    /// copying them.
    pub fn unpack_owned(raw: Vec<u8>) -> Result<Self, PacketError> {
        Self::unpack_with::<true, _>(raw)
    }

    /// Unpack owned wire bytes into fields, leaving `packet_hash` zeroed.
    /// Callers must hash the packet with [`RawPacket::hash_in_place`] before
    /// anything reads `packet_hash`.
    pub(crate) fn unpack_unhashed(raw: Vec<u8>) -> Result<Self, PacketError> {
        Self::unpack_with::<false, _>(raw)
    }

    fn unpack_with<const HASH: bool, B>(input: B) -> Result<Self, PacketError>
    where
        B: AsRef<[u8]> + Into<Vec<u8>>,
    {
        let raw = input.as_ref();
        if raw.len() < constants::HEADER_MINSIZE {
            return Err(PacketError::TooShort);
        }

        let flags = PacketFlags::unpack(raw[0]);
        let hops = raw[1];
        if hops >= constants::PATHFINDER_M {
            return Err(PacketError::InvalidHopCount(hops));
        }

        let dst_len = constants::TRUNCATED_HASHLENGTH / 8; // 16

        if flags.header_type == constants::HEADER_2 {
            // HEADER_2: [flags:1][hops:1][transport_id:16][dest_hash:16][context:1][data:*]
            let min_len = 2 + dst_len * 2 + 1;
            if raw.len() < min_len {
                return Err(PacketError::TooShort);
            }

            let mut transport_id = [0u8; 16];
            transport_id.copy_from_slice(&raw[2..2 + dst_len]);

            let mut destination_hash = [0u8; 16];
            destination_hash.copy_from_slice(&raw[2 + dst_len..2 + 2 * dst_len]);

            let context = raw[2 + 2 * dst_len];
            if raw.len() == 2 + 2 * dst_len + 1 {
                return Err(PacketError::ZeroLengthData);
            }

            let packet_hash = if HASH {
                Self::compute_packet_hash(flags.header_type, raw)
            } else {
                [0; 32]
            };

            Ok(RawPacket {
                flags,
                hops,
                transport_id: Some(transport_id),
                destination_hash,
                context,
                raw: input.into(),
                packet_hash,
                rssi: None,
                snr: None,
            })
        } else if flags.header_type == constants::HEADER_1 {
            // HEADER_1: [flags:1][hops:1][dest_hash:16][context:1][data:*]
            let min_len = 2 + dst_len + 1;
            if raw.len() < min_len {
                return Err(PacketError::TooShort);
            }

            let mut destination_hash = [0u8; 16];
            destination_hash.copy_from_slice(&raw[2..2 + dst_len]);

            let context = raw[2 + dst_len];
            if raw.len() == 2 + dst_len + 1 {
                return Err(PacketError::ZeroLengthData);
            }

            let packet_hash = if HASH {
                Self::compute_packet_hash(flags.header_type, raw)
            } else {
                [0; 32]
            };

            Ok(RawPacket {
                flags,
                hops,
                transport_id: None,
                destination_hash,
                context,
                raw: input.into(),
                packet_hash,
                rssi: None,
                snr: None,
            })
        } else {
            Err(PacketError::InvalidHeaderType)
        }
    }

    /// Get the hashable part of the packet.
    ///
    /// From Python Packet.py:354-361:
    /// - Take raw[0] & 0x0F (mask out upper 4 bits of flags)
    /// - For HEADER_1: append raw[2:]
    /// - For HEADER_2: skip transport_id: append raw[18:]
    pub fn get_hashable_part(&self) -> Vec<u8> {
        Self::compute_hashable_part(self.flags.header_type, &self.raw)
    }

    fn hashable_tail(header_type: u8, raw: &[u8]) -> &[u8] {
        if header_type == constants::HEADER_2 {
            // Skip transport_id: raw[2..18] is transport_id (16 bytes)
            &raw[(constants::TRUNCATED_HASHLENGTH / 8 + 2)..]
        } else {
            &raw[2..]
        }
    }

    fn compute_hashable_part(header_type: u8, raw: &[u8]) -> Vec<u8> {
        let tail = Self::hashable_tail(header_type, raw);
        let mut hashable = Vec::with_capacity(1 + tail.len());
        hashable.push(raw[0] & 0b00001111);
        hashable.extend_from_slice(tail);
        hashable
    }

    /// SHA-256 of the hashable part, fed from the wire bytes without building
    /// the concatenated buffer that [`RawPacket::get_hashable_part`] returns.
    fn compute_packet_hash(header_type: u8, raw: &[u8]) -> [u8; 32] {
        let mut hasher = rns_crypto::sha256::Sha256::new();
        hasher.update(&[raw[0] & 0b00001111]);
        hasher.update(Self::hashable_tail(header_type, raw));
        hasher.digest()
    }

    /// Compute `packet_hash` from the packet's wire bytes.
    pub(crate) fn hash_in_place(&mut self) {
        self.packet_hash = Self::compute_packet_hash(self.flags.header_type, &self.raw);
    }

    /// Full SHA-256 hash of the hashable part.
    pub fn get_hash(&self) -> [u8; 32] {
        self.packet_hash
    }

    /// Truncated hash (first 16 bytes) of the cached packet hash.
    ///
    /// Packet construction and unpacking compute `packet_hash` once; routing
    /// paths use this prefix instead of hashing the raw packet again.
    pub fn get_truncated_hash(&self) -> [u8; 16] {
        let mut result = [0u8; 16];
        result.copy_from_slice(&self.packet_hash[..16]);
        result
    }
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn raw_only_packing_preserves_wire_layout_and_limits() {
        for header in [constants::HEADER_1, constants::HEADER_2] {
            for transport in [None, Some([0xBB; 16])] {
                for len in [0, 1, 464, 16348] {
                    let flags = PacketFlags {
                        header_type: header,
                        context_flag: constants::FLAG_UNSET,
                        transport_type: constants::TRANSPORT_BROADCAST,
                        destination_type: constants::DESTINATION_LINK,
                        packet_type: constants::PACKET_TYPE_DATA,
                    };
                    let data = vec![0xCC; len];
                    let mut expected = vec![flags.pack(), 7];
                    if header == constants::HEADER_2 {
                        expected.extend_from_slice(&[0xBB; 16]);
                    }
                    expected.extend_from_slice(&[0xAA; 16]);
                    expected.push(constants::CONTEXT_RESOURCE);
                    expected.extend_from_slice(&data);
                    for limit in [0, expected.len() - 1, expected.len(), expected.len() + 1] {
                        let result = RawPacket::pack_raw_with_max_mtu(
                            flags,
                            7,
                            &[0xAA; 16],
                            transport.as_ref(),
                            constants::CONTEXT_RESOURCE,
                            &data,
                            limit,
                        );
                        if header == constants::HEADER_2 && transport.is_none() {
                            assert!(matches!(result, Err(PacketError::MissingTransportId)));
                        } else if limit < expected.len() {
                            assert!(matches!(result, Err(PacketError::ExceedsMtu)));
                        } else {
                            assert_eq!(result.unwrap(), expected);
                            let (raw, hash) = RawPacket::pack_raw_with_hash_with_max_mtu(
                                flags,
                                7,
                                &[0xAA; 16],
                                transport.as_ref(),
                                constants::CONTEXT_RESOURCE,
                                &data,
                                limit,
                            )
                            .unwrap();
                            assert_eq!(raw, expected);
                            if len == 0 {
                                assert!(matches!(
                                    RawPacket::unpack(&raw),
                                    Err(PacketError::ZeroLengthData)
                                ));
                            } else {
                                assert_eq!(RawPacket::unpack(&raw).unwrap().packet_hash, hash);
                            }
                        }
                    }
                }
            }
        }
    }

    #[test]
    fn test_flags_pack_header1_data_single_broadcast() {
        let flags = PacketFlags {
            header_type: constants::HEADER_1,
            context_flag: constants::FLAG_UNSET,
            transport_type: constants::TRANSPORT_BROADCAST,
            destination_type: constants::DESTINATION_SINGLE,
            packet_type: constants::PACKET_TYPE_DATA,
        };
        assert_eq!(flags.pack(), 0x00);
    }

    #[test]
    fn test_flags_pack_header2_announce_single_transport() {
        let flags = PacketFlags {
            header_type: constants::HEADER_2,
            context_flag: constants::FLAG_UNSET,
            transport_type: constants::TRANSPORT_TRANSPORT,
            destination_type: constants::DESTINATION_SINGLE,
            packet_type: constants::PACKET_TYPE_ANNOUNCE,
        };
        // 0b01010001 = 0x51
        assert_eq!(flags.pack(), 0x51);
    }

    #[test]
    fn test_flags_roundtrip() {
        for byte in 0..=0x7Fu8 {
            let flags = PacketFlags::unpack(byte);
            assert_eq!(flags.pack(), byte);
        }
    }

    #[test]
    fn test_pack_header1() {
        let dest_hash = [0xAA; 16];
        let data = b"hello";
        let flags = PacketFlags {
            header_type: constants::HEADER_1,
            context_flag: constants::FLAG_UNSET,
            transport_type: constants::TRANSPORT_BROADCAST,
            destination_type: constants::DESTINATION_SINGLE,
            packet_type: constants::PACKET_TYPE_DATA,
        };

        let pkt =
            RawPacket::pack(flags, 0, &dest_hash, None, constants::CONTEXT_NONE, data).unwrap();

        // Verify layout: [flags:1][hops:1][dest:16][context:1][data:5] = 24 bytes
        assert_eq!(pkt.raw.len(), 24);
        assert_eq!(pkt.raw[0], 0x00); // flags
        assert_eq!(pkt.raw[1], 0x00); // hops
        assert_eq!(&pkt.raw[2..18], &dest_hash); // dest hash
        assert_eq!(pkt.raw[18], 0x00); // context
        assert_eq!(&pkt.raw[19..], b"hello"); // data
    }

    #[test]
    fn test_pack_header2() {
        let dest_hash = [0xAA; 16];
        let transport_id = [0xBB; 16];
        let data = b"world";
        let flags = PacketFlags {
            header_type: constants::HEADER_2,
            context_flag: constants::FLAG_UNSET,
            transport_type: constants::TRANSPORT_TRANSPORT,
            destination_type: constants::DESTINATION_SINGLE,
            packet_type: constants::PACKET_TYPE_ANNOUNCE,
        };

        let pkt = RawPacket::pack(
            flags,
            3,
            &dest_hash,
            Some(&transport_id),
            constants::CONTEXT_NONE,
            data,
        )
        .unwrap();

        // Layout: [flags:1][hops:1][transport:16][dest:16][context:1][data:5] = 40 bytes
        assert_eq!(pkt.raw.len(), 40);
        assert_eq!(pkt.raw[0], flags.pack());
        assert_eq!(pkt.raw[1], 3);
        assert_eq!(&pkt.raw[2..18], &transport_id);
        assert_eq!(&pkt.raw[18..34], &dest_hash);
        assert_eq!(pkt.raw[34], 0x00);
        assert_eq!(&pkt.raw[35..], b"world");
    }

    #[test]
    fn test_unpack_roundtrip_header1() {
        let dest_hash = [0x11; 16];
        let data = b"test data";
        let flags = PacketFlags {
            header_type: constants::HEADER_1,
            context_flag: constants::FLAG_UNSET,
            transport_type: constants::TRANSPORT_BROADCAST,
            destination_type: constants::DESTINATION_SINGLE,
            packet_type: constants::PACKET_TYPE_DATA,
        };

        let pkt = RawPacket::pack(
            flags,
            5,
            &dest_hash,
            None,
            constants::CONTEXT_RESOURCE,
            data,
        )
        .unwrap();
        let unpacked = RawPacket::unpack(&pkt.raw).unwrap();

        assert_eq!(unpacked.flags, flags);
        assert_eq!(unpacked.hops, 5);
        assert!(unpacked.transport_id.is_none());
        assert_eq!(unpacked.destination_hash, dest_hash);
        assert_eq!(unpacked.context, constants::CONTEXT_RESOURCE);
        assert_eq!(unpacked.data(), data);
        assert_eq!(unpacked.packet_hash, pkt.packet_hash);
    }

    #[test]
    fn test_unpack_roundtrip_header2() {
        let dest_hash = [0x22; 16];
        let transport_id = [0x33; 16];
        let data = b"transported";
        let flags = PacketFlags {
            header_type: constants::HEADER_2,
            context_flag: constants::FLAG_SET,
            transport_type: constants::TRANSPORT_TRANSPORT,
            destination_type: constants::DESTINATION_SINGLE,
            packet_type: constants::PACKET_TYPE_ANNOUNCE,
        };

        let pkt = RawPacket::pack(
            flags,
            2,
            &dest_hash,
            Some(&transport_id),
            constants::CONTEXT_NONE,
            data,
        )
        .unwrap();
        let unpacked = RawPacket::unpack(&pkt.raw).unwrap();

        assert_eq!(unpacked.flags, flags);
        assert_eq!(unpacked.hops, 2);
        assert_eq!(unpacked.transport_id.unwrap(), transport_id);
        assert_eq!(unpacked.destination_hash, dest_hash);
        assert_eq!(unpacked.context, constants::CONTEXT_NONE);
        assert_eq!(unpacked.data(), data);
        assert_eq!(unpacked.packet_hash, pkt.packet_hash);
    }

    #[test]
    fn truncated_hash_is_derived_from_cached_packet_hash() {
        let mut packet = RawPacket::pack(
            PacketFlags {
                header_type: constants::HEADER_1,
                context_flag: constants::FLAG_UNSET,
                transport_type: constants::TRANSPORT_BROADCAST,
                destination_type: constants::DESTINATION_SINGLE,
                packet_type: constants::PACKET_TYPE_DATA,
            },
            1,
            &[0x42; 16],
            None,
            constants::CONTEXT_NONE,
            b"cached hash",
        )
        .unwrap();
        let expected: [u8; 16] = packet.packet_hash[..16].try_into().unwrap();

        // Changing the retained wire buffer demonstrates that this accessor is
        // a prefix operation, not a second hash computation.
        let last = packet.raw.len() - 1;
        packet.raw[last] ^= 0xff;

        assert_eq!(packet.get_truncated_hash(), expected);
    }

    #[test]
    fn test_unpack_too_short() {
        assert!(RawPacket::unpack(&[0x00; 5]).is_err());
    }

    #[test]
    fn unpack_rejects_zero_length_data_for_both_header_types() {
        for header_type in [constants::HEADER_1, constants::HEADER_2] {
            let packet = RawPacket::pack(
                PacketFlags {
                    header_type,
                    context_flag: constants::FLAG_UNSET,
                    transport_type: constants::TRANSPORT_BROADCAST,
                    destination_type: constants::DESTINATION_SINGLE,
                    packet_type: constants::PACKET_TYPE_DATA,
                },
                0,
                &[0x42; 16],
                (header_type == constants::HEADER_2).then_some(&[0x24; 16]),
                constants::CONTEXT_NONE,
                b"",
            )
            .unwrap();
            assert!(matches!(
                RawPacket::unpack(&packet.raw),
                Err(PacketError::ZeroLengthData)
            ));
        }
    }

    #[test]
    fn unpack_enforces_pathfinder_hop_boundary_but_pack_remains_permissive() {
        let flags = PacketFlags {
            header_type: constants::HEADER_1,
            context_flag: constants::FLAG_UNSET,
            transport_type: constants::TRANSPORT_BROADCAST,
            destination_type: constants::DESTINATION_SINGLE,
            packet_type: constants::PACKET_TYPE_DATA,
        };
        let accepted = RawPacket::pack(flags, 127, &[1; 16], None, 0, b"x").unwrap();
        assert_eq!(RawPacket::unpack(&accepted.raw).unwrap().hops, 127);

        for hops in [128, 255] {
            let packed = RawPacket::pack(flags, hops, &[1; 16], None, 0, b"x").unwrap();
            assert!(matches!(
                RawPacket::unpack(&packed.raw),
                Err(PacketError::InvalidHopCount(value)) if value == hops
            ));
        }
    }

    #[test]
    fn test_pack_exceeds_mtu() {
        let flags = PacketFlags {
            header_type: constants::HEADER_1,
            context_flag: constants::FLAG_UNSET,
            transport_type: constants::TRANSPORT_BROADCAST,
            destination_type: constants::DESTINATION_SINGLE,
            packet_type: constants::PACKET_TYPE_DATA,
        };
        let data = [0u8; 500]; // way too much data
        let result = RawPacket::pack(flags, 0, &[0; 16], None, 0, &data);
        assert!(result.is_err());
    }

    #[test]
    fn test_header2_missing_transport_id() {
        let flags = PacketFlags {
            header_type: constants::HEADER_2,
            context_flag: constants::FLAG_UNSET,
            transport_type: constants::TRANSPORT_TRANSPORT,
            destination_type: constants::DESTINATION_SINGLE,
            packet_type: constants::PACKET_TYPE_ANNOUNCE,
        };
        let result = RawPacket::pack(flags, 0, &[0; 16], None, 0, b"data");
        assert!(result.is_err());
    }

    #[test]
    fn test_hashable_part_header1_masks_upper_flags() {
        let dest_hash = [0xCC; 16];
        let flags = PacketFlags {
            header_type: constants::HEADER_1,
            context_flag: constants::FLAG_SET,
            transport_type: constants::TRANSPORT_BROADCAST,
            destination_type: constants::DESTINATION_SINGLE,
            packet_type: constants::PACKET_TYPE_DATA,
        };

        let pkt =
            RawPacket::pack(flags, 0, &dest_hash, None, constants::CONTEXT_NONE, b"test").unwrap();
        let hashable = pkt.get_hashable_part();

        // First byte should have upper 4 bits masked out
        assert_eq!(hashable[0], pkt.raw[0] & 0x0F);
        // Rest should be raw[2:]
        assert_eq!(&hashable[1..], &pkt.raw[2..]);
    }

    #[test]
    fn test_hashable_part_header2_strips_transport_id() {
        let dest_hash = [0xDD; 16];
        let transport_id = [0xEE; 16];
        let flags = PacketFlags {
            header_type: constants::HEADER_2,
            context_flag: constants::FLAG_UNSET,
            transport_type: constants::TRANSPORT_TRANSPORT,
            destination_type: constants::DESTINATION_SINGLE,
            packet_type: constants::PACKET_TYPE_ANNOUNCE,
        };

        let pkt = RawPacket::pack(
            flags,
            0,
            &dest_hash,
            Some(&transport_id),
            constants::CONTEXT_NONE,
            b"data",
        )
        .unwrap();
        let hashable = pkt.get_hashable_part();

        // First byte: flags masked
        assert_eq!(hashable[0], pkt.raw[0] & 0x0F);
        // Should skip transport_id: raw[18:] = dest_hash + context + data
        assert_eq!(&hashable[1..], &pkt.raw[18..]);
    }
}