fips/src/proto/discovery/wire.rs

//! Discovery messages: LookupRequest and LookupResponse.

use crate::NodeAddr;
use crate::proto::Error;
use crate::proto::codec::Reader;
use crate::proto::stp::TreeCoordinate;
use crate::proto::stp::{decode_coords, encode_coords};
use secp256k1::schnorr::Signature;

/// Request to discover a node's coordinates.
///
/// Routed through the spanning tree via bloom-filter-guided forwarding.
/// Each transit node forwards only to tree peers whose bloom filter
/// contains the target. TTL limits propagation depth.
#[derive(Clone, Debug)]
pub struct LookupRequest {
    /// Unique request identifier.
    pub request_id: u64,
    /// Node we're looking for.
    pub target: NodeAddr,
    /// Who's asking (for response routing).
    pub origin: NodeAddr,
    /// Origin's coordinates (for return path).
    pub origin_coords: TreeCoordinate,
    /// Remaining propagation hops.
    pub ttl: u8,
    /// Minimum transport MTU the origin requires for a viable route.
    /// 0 means no requirement.
    pub min_mtu: u16,
}

impl LookupRequest {
    /// Create a new lookup request.
    pub fn new(
        request_id: u64,
        target: NodeAddr,
        origin: NodeAddr,
        origin_coords: TreeCoordinate,
        ttl: u8,
        min_mtu: u16,
    ) -> Self {
        Self {
            request_id,
            target,
            origin,
            origin_coords,
            ttl,
            min_mtu,
        }
    }

    /// Decrement TTL for forwarding.
    ///
    /// Returns false if TTL was already 0.
    pub fn forward(&mut self) -> bool {
        if self.ttl == 0 {
            return false;
        }
        self.ttl -= 1;
        true
    }

    /// Check if this request can still be forwarded.
    pub fn can_forward(&self) -> bool {
        self.ttl > 0
    }

    /// Encode as wire format (includes msg_type byte).
    ///
    /// Format: `[0x30][request_id:8][target:16][origin:16][ttl:1][min_mtu:2]`
    ///         `[origin_coords_cnt:2][origin_coords:16×n]`
    pub fn encode(&self) -> Vec<u8> {
        let mut buf = Vec::with_capacity(46 + self.origin_coords.depth() * 16);

        buf.push(0x30); // msg_type
        buf.extend_from_slice(&self.request_id.to_le_bytes());
        buf.extend_from_slice(self.target.as_bytes());
        buf.extend_from_slice(self.origin.as_bytes());
        buf.push(self.ttl);
        buf.extend_from_slice(&self.min_mtu.to_le_bytes());
        encode_coords(&self.origin_coords, &mut buf);

        buf
    }

    /// Decode from wire format (after msg_type byte has been consumed).
    pub fn decode(payload: &[u8]) -> Result<Self, Error> {
        // Minimum: request_id(8) + target(16) + origin(16) + ttl(1) + min_mtu(2)
        //          + coords_count(2) = 45 bytes
        let mut reader = Reader::new(payload);
        reader.require(45)?;

        let request_id = reader.read_u64_le()?;

        let target = NodeAddr::from_bytes(reader.read_array::<16>()?);

        let origin = NodeAddr::from_bytes(reader.read_array::<16>()?);

        let ttl = reader.read_u8()?;

        let min_mtu = reader.read_u16_le()?;

        let (origin_coords, _consumed) = decode_coords(reader.rest())?;

        Ok(Self {
            request_id,
            target,
            origin,
            origin_coords,
            ttl,
            min_mtu,
        })
    }
}

/// Response to a lookup request with target's coordinates.
///
/// Routed back to the origin using the origin_coords from the request.
#[derive(Clone, Debug)]
pub struct LookupResponse {
    /// Echoed request identifier.
    pub request_id: u64,
    /// The target node.
    pub target: NodeAddr,
    /// Minimum transport MTU along the response path.
    ///
    /// Initialized to `u16::MAX` by the target. Each transit node applies
    /// `path_mtu = path_mtu.min(outgoing_link_mtu)` when forwarding.
    /// NOT included in the proof signature (transit annotation).
    pub path_mtu: u16,
    /// Target's coordinates in the tree.
    pub target_coords: TreeCoordinate,
    /// Proof that target authorized this response (signature over request).
    pub proof: Signature,
}

impl LookupResponse {
    /// Create a new lookup response.
    ///
    /// `path_mtu` is initialized to `u16::MAX` by the target; transit
    /// nodes reduce it as they forward.
    pub fn new(
        request_id: u64,
        target: NodeAddr,
        target_coords: TreeCoordinate,
        proof: Signature,
    ) -> Self {
        Self {
            request_id,
            target,
            path_mtu: u16::MAX,
            target_coords,
            proof,
        }
    }

    /// Get the bytes that should be signed as proof.
    ///
    /// Format: request_id (8) || target (16) || coords_encoding (2 + 16×n)
    pub fn proof_bytes(
        request_id: u64,
        target: &NodeAddr,
        target_coords: &TreeCoordinate,
    ) -> Vec<u8> {
        let coord_size = 2 + target_coords.entries().len() * 16;
        let mut bytes = Vec::with_capacity(24 + coord_size);
        bytes.extend_from_slice(&request_id.to_le_bytes());
        bytes.extend_from_slice(target.as_bytes());
        encode_coords(target_coords, &mut bytes);
        bytes
    }

    /// Encode as wire format (includes msg_type byte).
    ///
    /// Format: `[0x31][request_id:8][target:16][path_mtu:2][target_coords_cnt:2][target_coords:16×n][proof:64]`
    pub fn encode(&self) -> Vec<u8> {
        let mut buf = Vec::with_capacity(93 + self.target_coords.depth() * 16);

        buf.push(0x31); // msg_type
        buf.extend_from_slice(&self.request_id.to_le_bytes());
        buf.extend_from_slice(self.target.as_bytes());
        buf.extend_from_slice(&self.path_mtu.to_le_bytes());
        encode_coords(&self.target_coords, &mut buf);
        buf.extend_from_slice(self.proof.as_ref());

        buf
    }

    /// Decode from wire format (after msg_type byte has been consumed).
    pub fn decode(payload: &[u8]) -> Result<Self, Error> {
        // Minimum: request_id(8) + target(16) + path_mtu(2) + coords_count(2) + proof(64) = 92
        let mut reader = Reader::new(payload);
        reader.require(92)?;

        let request_id = reader.read_u64_le()?;

        let target = NodeAddr::from_bytes(reader.read_array::<16>()?);

        let path_mtu = reader.read_u16_le()?;

        let (target_coords, consumed) = decode_coords(reader.rest())?;
        reader.advance(consumed);

        let proof = Signature::from_slice(reader.read_bytes(64)?)
            .map_err(|_| Error::Malformed("bad proof signature"))?;

        Ok(Self {
            request_id,
            target,
            path_mtu,
            target_coords,
            proof,
        })
    }
}