rns_core/

packet.rs

use core::fmt;

use alloc::vec::Vec;
use sha2::Digest;

use crate::buffer::StaticBuffer;
use crate::crypt::fernet::{FERNET_MAX_PADDING_SIZE, FERNET_OVERHEAD_SIZE};
use crate::error::RnsError;
use crate::hash::AddressHash;
use crate::hash::Hash;
use crate::hash::ADDRESS_HASH_SIZE;

// Match Python Reticulum default MTU (500) minus max header and IFAC sizes.
// 500 - (2 + 1 + 16*2) - 1 = 464
pub const PACKET_MDU: usize = 464usize;
pub const LXMF_MAX_PAYLOAD: usize = PACKET_MDU - FERNET_OVERHEAD_SIZE - FERNET_MAX_PADDING_SIZE;
pub const PACKET_IFAC_MAX_LENGTH: usize = 64usize;

#[derive(Debug, PartialEq, Eq, Copy, Clone)]
pub enum IfacFlag {
    Open = 0b0,
    Authenticated = 0b1,
}

impl From<u8> for IfacFlag {
    fn from(value: u8) -> Self {
        match value {
            0 => IfacFlag::Open,
            1 => IfacFlag::Authenticated,
            _ => IfacFlag::Open,
        }
    }
}

#[derive(Debug, PartialEq, Eq, Copy, Clone)]
pub enum HeaderType {
    Type1 = 0b0,
    Type2 = 0b1,
}

impl From<u8> for HeaderType {
    fn from(value: u8) -> Self {
        match value & 0b1 {
            0 => HeaderType::Type1,
            1 => HeaderType::Type2,
            _ => HeaderType::Type1,
        }
    }
}

#[derive(Debug, PartialEq, Eq, Copy, Clone)]
pub enum PropagationType {
    Broadcast = 0b0,
    Transport = 0b1,
}

impl From<u8> for PropagationType {
    fn from(value: u8) -> Self {
        match value & 0b1 {
            0b0 => PropagationType::Broadcast,
            0b1 => PropagationType::Transport,
            _ => PropagationType::Broadcast,
        }
    }
}

#[derive(Debug, PartialEq, Eq, Copy, Clone)]
pub enum ContextFlag {
    Unset = 0b0,
    Set = 0b1,
}

impl From<u8> for ContextFlag {
    fn from(value: u8) -> Self {
        match value & 0b1 {
            0b0 => ContextFlag::Unset,
            0b1 => ContextFlag::Set,
            _ => ContextFlag::Unset,
        }
    }
}

#[derive(Debug, PartialEq, Eq, Copy, Clone)]
pub enum DestinationType {
    Single = 0b00,
    Group = 0b01,
    Plain = 0b10,
    Link = 0b11,
}

impl From<u8> for DestinationType {
    fn from(value: u8) -> Self {
        match value & 0b11 {
            0b00 => DestinationType::Single,
            0b01 => DestinationType::Group,
            0b10 => DestinationType::Plain,
            0b11 => DestinationType::Link,
            _ => DestinationType::Single,
        }
    }
}

#[derive(Debug, PartialEq, Eq, Copy, Clone)]
pub enum PacketType {
    Data = 0b00,
    Announce = 0b01,
    LinkRequest = 0b10,
    Proof = 0b11,
}

impl From<u8> for PacketType {
    fn from(value: u8) -> Self {
        match value & 0b11 {
            0b00 => PacketType::Data,
            0b01 => PacketType::Announce,
            0b10 => PacketType::LinkRequest,
            0b11 => PacketType::Proof,
            _ => PacketType::Data,
        }
    }
}

#[derive(Debug, PartialEq, Eq, Copy, Clone)]
pub enum PacketContext {
    None = 0x00,                    // Generic data packet
    Resource = 0x01,                // Packet is part of a resource
    ResourceAdvrtisement = 0x02,    // Packet is a resource advertisement
    ResourceRequest = 0x03,         // Packet is a resource part request
    ResourceHashUpdate = 0x04,      // Packet is a resource hashmap update
    ResourceProof = 0x05,           // Packet is a resource proof
    ResourceInitiatorCancel = 0x06, // Packet is a resource initiator cancel message
    ResourceReceiverCancel = 0x07,  // Packet is a resource receiver cancel message
    CacheRequest = 0x08,            // Packet is a cache request
    Request = 0x09,                 // Packet is a request
    Response = 0x0A,                // Packet is a response to a request
    PathResponse = 0x0B,            // Packet is a response to a path request
    Command = 0x0C,                 // Packet is a command
    CommandStatus = 0x0D,           // Packet is a status of an executed command
    Channel = 0x0E,                 // Packet contains link channel data
    KeepAlive = 0xFA,               // Packet is a keepalive packet
    LinkIdentify = 0xFB,            // Packet is a link peer identification proof
    LinkClose = 0xFC,               // Packet is a link close message
    LinkProof = 0xFD,               // Packet is a link packet proof
    LinkRTT = 0xFE,                 // Packet is a link request round-trip time measurement
    LinkRequestProof = 0xFF,        // Packet is a link request proof
}

impl From<u8> for PacketContext {
    fn from(value: u8) -> Self {
        match value {
            0x01 => PacketContext::Resource,
            0x02 => PacketContext::ResourceAdvrtisement,
            0x03 => PacketContext::ResourceRequest,
            0x04 => PacketContext::ResourceHashUpdate,
            0x05 => PacketContext::ResourceProof,
            0x06 => PacketContext::ResourceInitiatorCancel,
            0x07 => PacketContext::ResourceReceiverCancel,
            0x08 => PacketContext::CacheRequest,
            0x09 => PacketContext::Request,
            0x0A => PacketContext::Response,
            0x0B => PacketContext::PathResponse,
            0x0C => PacketContext::Command,
            0x0D => PacketContext::CommandStatus,
            0x0E => PacketContext::Channel,
            0xFA => PacketContext::KeepAlive,
            0xFB => PacketContext::LinkIdentify,
            0xFC => PacketContext::LinkClose,
            0xFD => PacketContext::LinkProof,
            0xFE => PacketContext::LinkRTT,
            0xFF => PacketContext::LinkRequestProof,
            _ => PacketContext::None,
        }
    }
}

#[derive(Debug, PartialEq, Eq, Copy, Clone)]
pub struct Header {
    pub ifac_flag: IfacFlag,
    pub header_type: HeaderType,
    pub context_flag: ContextFlag,
    pub propagation_type: PropagationType,
    pub destination_type: DestinationType,
    pub packet_type: PacketType,
    pub hops: u8,
}

impl Default for Header {
    fn default() -> Self {
        Self {
            ifac_flag: IfacFlag::Open,
            header_type: HeaderType::Type1,
            context_flag: ContextFlag::Unset,
            propagation_type: PropagationType::Broadcast,
            destination_type: DestinationType::Single,
            packet_type: PacketType::Data,
            hops: 0,
        }
    }
}

impl Header {
    pub fn to_meta(&self) -> u8 {
        (self.ifac_flag as u8) << 7
            | (self.header_type as u8) << 6
            | (self.context_flag as u8) << 5
            | (self.propagation_type as u8) << 4
            | (self.destination_type as u8) << 2
            | (self.packet_type as u8)
    }

    pub fn from_meta(meta: u8) -> Self {
        Self {
            ifac_flag: IfacFlag::from(meta >> 7),
            header_type: HeaderType::from(meta >> 6),
            context_flag: ContextFlag::from(meta >> 5),
            propagation_type: PropagationType::from(meta >> 4),
            destination_type: DestinationType::from(meta >> 2),
            packet_type: PacketType::from(meta),
            hops: 0,
        }
    }
}

impl fmt::Display for Header {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        write!(
            f,
            "{:b}{:b}{:b}{:b}{:0>2b}{:0>2b}.{}",
            self.ifac_flag as u8,
            self.header_type as u8,
            self.context_flag as u8,
            self.propagation_type as u8,
            self.destination_type as u8,
            self.packet_type as u8,
            self.hops,
        )
    }
}

pub type PacketDataBuffer = StaticBuffer<PACKET_MDU>;

#[derive(Debug, PartialEq, Eq, Copy, Clone)]
pub struct PacketIfac {
    pub access_code: [u8; PACKET_IFAC_MAX_LENGTH],
    pub length: usize,
}

impl PacketIfac {
    pub fn new_from_slice(slice: &[u8]) -> Self {
        let mut access_code = [0u8; PACKET_IFAC_MAX_LENGTH];
        access_code[..slice.len()].copy_from_slice(slice);
        Self { access_code, length: slice.len() }
    }

    pub fn as_slice(&self) -> &[u8] {
        &self.access_code[..self.length]
    }
}

#[derive(Debug, PartialEq, Eq, Copy, Clone)]
pub struct Packet {
    pub header: Header,
    pub ifac: Option<PacketIfac>,
    pub destination: AddressHash,
    pub transport: Option<AddressHash>,
    pub context: PacketContext,
    pub data: PacketDataBuffer,
}

impl Packet {
    pub const LXMF_MAX_PAYLOAD: usize = LXMF_MAX_PAYLOAD;

    pub fn from_bytes(bytes: &[u8]) -> Result<Self, RnsError> {
        let min_len = 2 + ADDRESS_HASH_SIZE + 1;
        if bytes.len() < min_len {
            return Err(RnsError::InvalidArgument);
        }

        let flags = bytes[0];
        let hops = bytes[1];

        let mut header = Header::from_meta(flags);
        header.hops = hops;

        let mut idx = 2;

        let transport = if header.header_type == HeaderType::Type2 {
            if bytes.len() < idx + ADDRESS_HASH_SIZE {
                return Err(RnsError::InvalidArgument);
            }
            let mut raw = [0u8; ADDRESS_HASH_SIZE];
            raw.copy_from_slice(&bytes[idx..idx + ADDRESS_HASH_SIZE]);
            idx += ADDRESS_HASH_SIZE;
            Some(AddressHash::new(raw))
        } else {
            None
        };

        if bytes.len() < idx + ADDRESS_HASH_SIZE + 1 {
            return Err(RnsError::InvalidArgument);
        }

        let mut dest_raw = [0u8; ADDRESS_HASH_SIZE];
        dest_raw.copy_from_slice(&bytes[idx..idx + ADDRESS_HASH_SIZE]);
        idx += ADDRESS_HASH_SIZE;
        let destination = AddressHash::new(dest_raw);

        let context = PacketContext::from(bytes[idx]);
        idx += 1;

        let data = PacketDataBuffer::new_from_slice(&bytes[idx..]);

        Ok(Self { header, ifac: None, destination, transport, context, data })
    }

    pub fn to_bytes(&self) -> Result<Vec<u8>, RnsError> {
        let mut out = Vec::with_capacity(2 + ADDRESS_HASH_SIZE + 1 + self.data.len());

        out.push(self.header.to_meta());
        out.push(self.header.hops);

        if self.header.header_type == HeaderType::Type2 {
            let transport = self.transport.ok_or(RnsError::InvalidArgument)?;
            out.extend_from_slice(transport.as_slice());
        }

        out.extend_from_slice(self.destination.as_slice());
        out.push(self.context as u8);
        out.extend_from_slice(self.data.as_slice());

        Ok(out)
    }

    pub fn hash(&self) -> Hash {
        Hash::new(
            Hash::generator()
                .chain_update([self.header.to_meta() & 0b00001111])
                .chain_update(self.destination.as_slice())
                .chain_update([self.context as u8])
                .chain_update(self.data.as_slice())
                .finalize()
                .into(),
        )
    }

    pub fn fragment_for_lxmf(data: &[u8]) -> Result<Vec<Packet>, RnsError> {
        let mut out = Vec::new();
        for chunk in data.chunks(Self::LXMF_MAX_PAYLOAD) {
            let packet = Packet { data: StaticBuffer::new_from_slice(chunk), ..Default::default() };
            out.push(packet);
        }
        Ok(out)
    }
}

impl Default for Packet {
    fn default() -> Self {
        Self {
            header: Default::default(),
            destination: AddressHash::new_empty(),
            data: Default::default(),
            ifac: None,
            transport: None,
            context: crate::packet::PacketContext::None,
        }
    }
}

impl fmt::Display for Packet {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        write!(f, "[{}", self.header)?;

        if let Some(transport) = self.transport {
            write!(f, " {}", transport)?;
        }

        write!(f, " {}", self.destination)?;

        write!(f, " 0x[{}]]", self.data.len())?;

        Ok(())
    }
}

#[cfg(test)]
mod tests {
    use super::{
        ContextFlag, DestinationType, Header, HeaderType, IfacFlag, PacketType, PropagationType,
    };

    #[test]
    fn header_meta_roundtrip_preserves_context_and_transport_bits() {
        let header = Header {
            ifac_flag: IfacFlag::Open,
            header_type: HeaderType::Type1,
            context_flag: ContextFlag::Set,
            propagation_type: PropagationType::Transport,
            destination_type: DestinationType::Single,
            packet_type: PacketType::Announce,
            hops: 0,
        };

        let meta = header.to_meta();
        assert_eq!(meta & 0b0010_0000, 0b0010_0000);
        assert_eq!(meta & 0b0001_0000, 0b0001_0000);

        let decoded = Header::from_meta(meta);
        assert_eq!(decoded.context_flag, ContextFlag::Set);
        assert_eq!(decoded.propagation_type, PropagationType::Transport);
    }
}