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SessionDatagram redesign: add src_addr, reclassify error signals

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Add src_addr to SessionDatagram envelope (34-byte header: msg_type +
src_addr + dest_addr + hop_limit) so transit routers can route error
signals back to the packet's originator.

Reclassify CoordsRequired/PathBroken as link-layer error signals
(plaintext inside SessionDatagram) rather than e2e encrypted session
messages. Transit routers generate these when forwarding fails and
route them to src_addr; if source is also unreachable, drop silently.

Remove redundant src_addr/dest_addr/hop_limit from SessionSetup,
SessionAck, and DataPacket (now in envelope). DataPacket header
reduced from 36 to 4 bytes. Remove PathBroken.original_src.

Fix routing loop vulnerability: gate bloom filter path on having
cached dest_coords to prevent blind forwarding between peers.
Simplify select_best_candidate() to require coordinates.

Fix gossip protocol type codes (0x11->0x20, 0x12->0x30, 0x13->0x31)
for consistency across all design docs.

All 5 design docs updated and cross-checked for consistency.
335 tests pass, zero warnings.
This commit is contained in:
Johnathan Corgan
2026-02-12 11:32:45 +00:00
parent 2f8e97c0ab
commit d41009b778
9 changed files with 535 additions and 349 deletions
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src/protocol/link.rs
+27 -7
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@@ -244,25 +244,45 @@ impl Disconnect {
// Session Datagram (Link-Layer Encapsulation)
// ============================================================================
/// Encapsulated session-layer datagram for forwarding.
/// Encapsulated session-layer datagram for multi-hop forwarding.
///
/// This is a link-layer message that carries an opaque, end-to-end encrypted
/// session-layer payload. Intermediate nodes route based on the destination
/// address but cannot decrypt the payload.
/// This is a link-layer message (type 0x40) that carries session-layer
/// payloads through the mesh. The envelope provides source and destination
/// addressing that transit routers use for forwarding decisions and error
/// routing.
///
/// ## Wire Format (34-byte fixed header)
///
/// | Offset | Field | Size | Description |
/// |--------|-----------|----------|--------------------------------|
/// | 0 | msg_type | 1 byte | 0x40 |
/// | 1 | src_addr | 16 bytes | Source node_addr |
/// | 17 | dest_addr | 16 bytes | Destination node_addr |
/// | 33 | hop_limit | 1 byte | Decremented each hop |
/// | 34 | payload | variable | Session-layer message |
///
/// The payload is either end-to-end encrypted (SessionSetup, SessionAck,
/// DataPacket) or plaintext link-layer error signals (CoordsRequired,
/// PathBroken) generated by transit routers.
#[derive(Clone, Debug)]
pub struct SessionDatagram {
/// Source node address (originator of this datagram).
/// For data traffic: the source endpoint.
/// For error signals: the transit router that generated the error.
pub src_addr: NodeAddr,
/// Destination node address (for routing decisions).
pub dest_addr: NodeAddr,
/// Hop limit (decremented at each hop).
/// Hop limit (decremented at each hop, dropped at zero).
pub hop_limit: u8,
/// Encrypted session-layer payload (opaque to intermediate nodes).
/// Session-layer payload (e2e encrypted or plaintext error signal).
pub payload: Vec<u8>,
}
impl SessionDatagram {
/// Create a new session datagram.
pub fn new(dest_addr: NodeAddr, payload: Vec<u8>) -> Self {
pub fn new(src_addr: NodeAddr, dest_addr: NodeAddr, payload: Vec<u8>) -> Self {
Self {
src_addr,
dest_addr,
hop_limit: 64,
payload,