fips/src/node/handlers/handshake.rs

//! Handshake handlers and connection promotion.

use crate::node::{Node, NodeError};
use crate::peer::{
    cross_connection_winner, ActivePeer, PeerConnection, PromotionResult,
};
use crate::transport::{Link, LinkDirection, LinkId, ReceivedPacket};
use crate::node::wire::{build_msg2, Msg1Header, Msg2Header};
use crate::PeerIdentity;
use std::time::Duration;
use tracing::{debug, info, warn};

impl Node {
    /// Handle handshake message 1 (phase 0x1).
    ///
    /// This creates a new inbound connection. Rate limiting is applied
    /// before any expensive crypto operations.
    pub(in crate::node) async fn handle_msg1(&mut self, packet: ReceivedPacket) {
        // === RATE LIMITING (before any processing) ===
        if !self.msg1_rate_limiter.start_handshake() {
            debug!(
                transport_id = %packet.transport_id,
                remote_addr = %packet.remote_addr,
                "Msg1 rate limited"
            );
            return;
        }

        // Parse header
        let header = match Msg1Header::parse(&packet.data) {
            Some(h) => h,
            None => {
                self.msg1_rate_limiter.complete_handshake();
                debug!("Invalid msg1 header");
                return;
            }
        };

        // Check for existing connection from this address.
        //
        // If we already have an *inbound* link from this address, drop the msg1
        // (duplicate or replay). But if we have an *outbound* link to this address
        // (we initiated to them AND they initiated to us), this is a cross-connection.
        // Allow it to proceed — promote_connection() will resolve via tie-breaker.
        let addr_key = (packet.transport_id, packet.remote_addr.clone());
        if let Some(&existing_link_id) = self.addr_to_link.get(&addr_key)
            && let Some(link) = self.links.get(&existing_link_id)
        {
            if link.direction() == LinkDirection::Inbound {
                self.msg1_rate_limiter.complete_handshake();
                debug!(
                    transport_id = %packet.transport_id,
                    remote_addr = %packet.remote_addr,
                    "Already have inbound connection from this address"
                );
                return;
            }
            // Outbound link to this address — cross-connection, allow msg1
            debug!(
                transport_id = %packet.transport_id,
                remote_addr = %packet.remote_addr,
                existing_link_id = %existing_link_id,
                "Cross-connection detected: have outbound, received inbound msg1"
                );
        }

        // === CRYPTO COST PAID HERE ===
        let link_id = self.allocate_link_id();
        let mut conn = PeerConnection::inbound_with_transport(
            link_id,
            packet.transport_id,
            packet.remote_addr.clone(),
            packet.timestamp_ms,
        );

        let our_keypair = self.identity.keypair();
        let noise_msg1 = &packet.data[header.noise_msg1_offset..];
        let msg2_response = match conn.receive_handshake_init(our_keypair, noise_msg1, packet.timestamp_ms) {
            Ok(m) => m,
            Err(e) => {
                self.msg1_rate_limiter.complete_handshake();
                debug!(
                    error = %e,
                    "Failed to process msg1"
                );
                return;
            }
        };

        // Learn peer identity from msg1
        let peer_identity = match conn.expected_identity() {
            Some(id) => *id,
            None => {
                self.msg1_rate_limiter.complete_handshake();
                warn!("Identity not learned from msg1");
                return;
            }
        };

        // Note: we don't early-return if peer is already in self.peers here.
        // promote_connection handles cross-connection resolution via tie-breaker.

        // Allocate our session index
        let our_index = match self.index_allocator.allocate() {
            Ok(idx) => idx,
            Err(e) => {
                self.msg1_rate_limiter.complete_handshake();
                warn!(error = %e, "Failed to allocate session index for inbound");
                return;
            }
        };

        conn.set_our_index(our_index);
        conn.set_their_index(header.sender_idx);

        // Create link
        let link = Link::connectionless(
            link_id,
            packet.transport_id,
            packet.remote_addr.clone(),
            LinkDirection::Inbound,
            Duration::from_millis(self.config.node.base_rtt_ms),
        );

        self.links.insert(link_id, link);
        self.addr_to_link.insert(addr_key, link_id);
        self.connections.insert(link_id, conn);

        // Build and send msg2 response
        let wire_msg2 = build_msg2(our_index, header.sender_idx, &msg2_response);

        if let Some(transport) = self.transports.get(&packet.transport_id) {
            match transport.send(&packet.remote_addr, &wire_msg2).await {
                Ok(bytes) => {
                    debug!(
                        link_id = %link_id,
                        our_index = %our_index,
                        their_index = %header.sender_idx,
                        bytes,
                        "Sent msg2 response"
                    );
                }
                Err(e) => {
                    warn!(
                        link_id = %link_id,
                        error = %e,
                        "Failed to send msg2"
                    );
                    // Clean up on failure
                    self.connections.remove(&link_id);
                    self.links.remove(&link_id);
                    self.addr_to_link.remove(&(packet.transport_id, packet.remote_addr));
                    let _ = self.index_allocator.free(our_index);
                    self.msg1_rate_limiter.complete_handshake();
                    return;
                }
            }
        }

        // Responder handshake is complete after receive_handshake_init (Noise IK
        // pattern: responder processes msg1 and generates msg2 in one step).
        // Promote the connection to active peer now.
        match self.promote_connection(link_id, peer_identity, packet.timestamp_ms) {
            Ok(result) => {
                match result {
                    PromotionResult::Promoted(node_addr) => {
                        info!(
                            node_addr = %node_addr,
                            link_id = %link_id,
                            our_index = %our_index,
                            "Inbound peer promoted to active"
                        );
                        // Send initial tree announce to new peer
                        if let Err(e) = self.send_tree_announce_to_peer(&node_addr).await {
                            debug!(peer = %node_addr, error = %e, "Failed to send initial TreeAnnounce");
                        }
                        // Schedule filter announce (sent on next tick via debounce)
                        self.bloom_state.mark_update_needed(node_addr);
                    }
                    PromotionResult::CrossConnectionWon { loser_link_id, node_addr } => {
                        // Clean up the losing connection's link
                        self.remove_link(&loser_link_id);
                        info!(
                            node_addr = %node_addr,
                            loser_link_id = %loser_link_id,
                            "Inbound cross-connection won, loser link cleaned up"
                        );
                        // Send initial tree announce to peer (new or reconnected)
                        if let Err(e) = self.send_tree_announce_to_peer(&node_addr).await {
                            debug!(peer = %node_addr, error = %e, "Failed to send initial TreeAnnounce");
                        }
                        // Schedule filter announce (sent on next tick via debounce)
                        self.bloom_state.mark_update_needed(node_addr);
                    }
                    PromotionResult::CrossConnectionLost { winner_link_id } => {
                        // This connection lost — clean up its link
                        self.remove_link(&link_id);
                        // Restore addr_to_link for the winner's link
                        self.addr_to_link.insert(
                            (packet.transport_id, packet.remote_addr.clone()),
                            winner_link_id,
                        );
                        info!(
                            winner_link_id = %winner_link_id,
                            "Inbound cross-connection lost, keeping existing"
                        );
                    }
                }
            }
            Err(e) => {
                warn!(
                    link_id = %link_id,
                    error = %e,
                    "Failed to promote inbound connection"
                );
                // Clean up on promotion failure
                self.remove_link(&link_id);
                let _ = self.index_allocator.free(our_index);
            }
        }

        self.msg1_rate_limiter.complete_handshake();
    }

    /// Handle handshake message 2 (phase 0x2).
    ///
    /// This completes an outbound handshake we initiated.
    pub(in crate::node) async fn handle_msg2(&mut self, packet: ReceivedPacket) {
        // Parse header
        let header = match Msg2Header::parse(&packet.data) {
            Some(h) => h,
            None => {
                debug!("Invalid msg2 header");
                return;
            }
        };

        // Look up our pending handshake by our sender_idx (receiver_idx in msg2)
        let key = (packet.transport_id, header.receiver_idx.as_u32());
        let link_id = match self.pending_outbound.get(&key) {
            Some(id) => *id,
            None => {
                debug!(
                    receiver_idx = %header.receiver_idx,
                    "No pending outbound handshake for index"
                );
                return;
            }
        };

        let conn = match self.connections.get_mut(&link_id) {
            Some(c) => c,
            None => {
                // Connection removed, clean up pending_outbound
                self.pending_outbound.remove(&key);
                return;
            }
        };

        // Process Noise msg2
        let noise_msg2 = &packet.data[header.noise_msg2_offset..];
        if let Err(e) = conn.complete_handshake(noise_msg2, packet.timestamp_ms) {
            warn!(
                link_id = %link_id,
                error = %e,
                "Handshake completion failed"
            );
            conn.mark_failed();
            return;
        }

        // Store their index
        conn.set_their_index(header.sender_idx);
        conn.set_source_addr(packet.remote_addr.clone());

        // Get peer identity for promotion
        let peer_identity = match conn.expected_identity() {
            Some(id) => *id,
            None => {
                warn!(link_id = %link_id, "No identity after handshake");
                return;
            }
        };

        let peer_node_addr = *peer_identity.node_addr();

        info!(
            node_addr = %peer_node_addr,
            link_id = %link_id,
            their_index = %header.sender_idx,
            "Outbound handshake completed"
        );

        // Cross-connection resolution: if the peer was already promoted via
        // our inbound handshake (we processed their msg1), both nodes initially
        // use mismatched sessions. The tie-breaker determines which handshake
        // wins: smaller node_addr's outbound.
        //
        // - Winner (smaller node): swap to outbound session + outbound indices
        // - Loser (larger node): keep inbound session + original their_index
        //
        // This ensures both nodes use the same Noise handshake (the winner's
        // outbound = the loser's inbound).
        if self.peers.contains_key(&peer_node_addr) {
            let our_outbound_wins = cross_connection_winner(
                self.identity.node_addr(),
                &peer_node_addr,
                true, // this IS our outbound
            );

            // Extract the outbound connection
            let mut conn = match self.connections.remove(&link_id) {
                Some(c) => c,
                None => {
                    self.pending_outbound.remove(&key);
                    return;
                }
            };

            if our_outbound_wins {
                // We're the smaller node. Swap to outbound session + indices.
                // The peer will keep their inbound session (complement of ours).
                let outbound_our_index = conn.our_index();
                let outbound_session = conn.take_session();

                let (outbound_session, outbound_our_index) =
                    match (outbound_session, outbound_our_index) {
                        (Some(s), Some(idx)) => (s, idx),
                        _ => {
                            warn!(node_addr = %peer_node_addr, "Incomplete outbound connection");
                            self.pending_outbound.remove(&key);
                            return;
                        }
                    };

                if let Some(peer) = self.peers.get_mut(&peer_node_addr) {
                    let old_our_index = peer.replace_session(
                        outbound_session,
                        outbound_our_index,
                        header.sender_idx,
                    );

                    // Update peers_by_index: remove old inbound index, add outbound
                    let transport_id = peer.transport_id().unwrap();
                    if let Some(old_idx) = old_our_index {
                        self.peers_by_index.remove(&(transport_id, old_idx.as_u32()));
                        let _ = self.index_allocator.free(old_idx);
                    }
                    self.peers_by_index.insert(
                        (transport_id, outbound_our_index.as_u32()),
                        peer_node_addr,
                    );

                    info!(
                        node_addr = %peer_node_addr,
                        new_our_index = %outbound_our_index,
                        new_their_index = %header.sender_idx,
                        "Cross-connection: swapped to outbound session (our outbound wins)"
                    );
                }
            } else {
                // We're the larger node. Keep our inbound session (it pairs
                // with the peer's outbound, which is the winning handshake).
                //
                // Do NOT update their_index here. Our their_index was set during
                // promote_connection() from the peer's msg1 sender_idx, which is
                // the peer's outbound our_index. After the peer (winner) swaps to
                // their outbound session, that index is exactly what they'll use.
                // The msg2 sender_idx we see here is the peer's INBOUND our_index,
                // which becomes stale after the peer swaps.
                let outbound_our_index = conn.our_index();

                if let Some(peer) = self.peers.get(&peer_node_addr) {
                    info!(
                        node_addr = %peer_node_addr,
                        kept_their_index = ?peer.their_index(),
                        "Cross-connection: keeping inbound session and original their_index (peer outbound wins)"
                    );
                }

                // Free the outbound's session index since we're not using it
                if let Some(idx) = outbound_our_index {
                    let _ = self.index_allocator.free(idx);
                }
            }

            // Clean up outbound connection state
            self.pending_outbound.remove(&key);
            self.remove_link(&link_id);

            // Send TreeAnnounce now that sessions are aligned
            if let Err(e) = self.send_tree_announce_to_peer(&peer_node_addr).await {
                debug!(peer = %peer_node_addr, error = %e, "Failed to send TreeAnnounce after cross-connection resolution");
            }
            // Schedule filter announce (sent on next tick via debounce)
            self.bloom_state.mark_update_needed(peer_node_addr);
            return;
        }

        // Normal path: promote to active peer
        match self.promote_connection(link_id, peer_identity, packet.timestamp_ms) {
            Ok(result) => {
                // Clean up pending_outbound
                self.pending_outbound.remove(&key);

                match result {
                    PromotionResult::Promoted(node_addr) => {
                        info!(
                            node_addr = %node_addr,
                            "Peer promoted to active"
                        );
                        // Send initial tree announce to new peer
                        if let Err(e) = self.send_tree_announce_to_peer(&node_addr).await {
                            debug!(peer = %node_addr, error = %e, "Failed to send initial TreeAnnounce");
                        }
                        // Schedule filter announce (sent on next tick via debounce)
                        self.bloom_state.mark_update_needed(node_addr);
                    }
                    PromotionResult::CrossConnectionWon { loser_link_id, node_addr } => {
                        // Clean up the losing connection's link
                        self.remove_link(&loser_link_id);
                        // Ensure addr_to_link points to the winning link
                        self.addr_to_link.insert(
                            (packet.transport_id, packet.remote_addr.clone()),
                            link_id,
                        );
                        info!(
                            node_addr = %node_addr,
                            loser_link_id = %loser_link_id,
                            "Outbound cross-connection won, loser link cleaned up"
                        );
                        // Send initial tree announce to peer (new or reconnected)
                        if let Err(e) = self.send_tree_announce_to_peer(&node_addr).await {
                            debug!(peer = %node_addr, error = %e, "Failed to send initial TreeAnnounce");
                        }
                        // Schedule filter announce (sent on next tick via debounce)
                        self.bloom_state.mark_update_needed(node_addr);
                    }
                    PromotionResult::CrossConnectionLost { winner_link_id } => {
                        // This connection lost — clean up its link
                        self.remove_link(&link_id);
                        // Ensure addr_to_link points to the winner's link
                        self.addr_to_link.insert(
                            (packet.transport_id, packet.remote_addr.clone()),
                            winner_link_id,
                        );
                        info!(
                            winner_link_id = %winner_link_id,
                            "Outbound cross-connection lost, keeping existing"
                        );
                    }
                }
            }
            Err(e) => {
                warn!(
                    link_id = %link_id,
                    error = %e,
                    "Failed to promote connection"
                );
            }
        }
    }

    /// Promote a connection to active peer after successful authentication.
    ///
    /// Handles cross-connection detection and resolution using tie-breaker rules.
    pub(in crate::node) fn promote_connection(
        &mut self,
        link_id: LinkId,
        verified_identity: PeerIdentity,
        current_time_ms: u64,
    ) -> Result<PromotionResult, NodeError> {
        // Remove the connection from pending
        let mut connection = self
            .connections
            .remove(&link_id)
            .ok_or(NodeError::ConnectionNotFound(link_id))?;

        // Verify handshake is complete and extract session
        if !connection.has_session() {
            return Err(NodeError::HandshakeIncomplete(link_id));
        }

        let noise_session = connection
            .take_session()
            .ok_or(NodeError::NoSession(link_id))?;

        let our_index = connection.our_index().ok_or_else(|| {
            NodeError::PromotionFailed {
                link_id,
                reason: "missing our_index".into(),
            }
        })?;
        let their_index = connection.their_index().ok_or_else(|| {
            NodeError::PromotionFailed {
                link_id,
                reason: "missing their_index".into(),
            }
        })?;
        let transport_id = connection.transport_id().ok_or_else(|| {
            NodeError::PromotionFailed {
                link_id,
                reason: "missing transport_id".into(),
            }
        })?;
        let current_addr = connection.source_addr().ok_or_else(|| {
            NodeError::PromotionFailed {
                link_id,
                reason: "missing source_addr".into(),
            }
        })?.clone();
        let link_stats = connection.link_stats().clone();

        let peer_node_addr = *verified_identity.node_addr();
        let is_outbound = connection.is_outbound();

        // Check for cross-connection
        if let Some(existing_peer) = self.peers.get(&peer_node_addr) {
            let existing_link_id = existing_peer.link_id();

            // Determine which connection wins
            let this_wins = cross_connection_winner(
                self.identity.node_addr(),
                &peer_node_addr,
                is_outbound,
            );

            if this_wins {
                // This connection wins, replace the existing peer
                let old_peer = self.peers.remove(&peer_node_addr).unwrap();
                let loser_link_id = old_peer.link_id();

                // Clean up old peer's index from peers_by_index
                if let (Some(old_tid), Some(old_idx)) =
                    (old_peer.transport_id(), old_peer.our_index())
                {
                    self.peers_by_index
                        .remove(&(old_tid, old_idx.as_u32()));
                    let _ = self.index_allocator.free(old_idx);
                }

                let mut new_peer = ActivePeer::with_session(
                    verified_identity,
                    link_id,
                    current_time_ms,
                    noise_session,
                    our_index,
                    their_index,
                    transport_id,
                    current_addr,
                    link_stats,
                    is_outbound,
                    &self.config.node.mmp,
                );
                new_peer.set_tree_announce_min_interval_ms(self.config.node.tree.announce_min_interval_ms);

                self.peers.insert(peer_node_addr, new_peer);
                self.peers_by_index
                    .insert((transport_id, our_index.as_u32()), peer_node_addr);
                self.retry_pending.remove(&peer_node_addr);
                self.register_identity(peer_node_addr, verified_identity.pubkey_full());

                info!(
                    node_addr = %peer_node_addr,
                    winner_link = %link_id,
                    loser_link = %loser_link_id,
                    "Cross-connection resolved: this connection won"
                );

                Ok(PromotionResult::CrossConnectionWon {
                    loser_link_id,
                    node_addr: peer_node_addr,
                })
            } else {
                // This connection loses, keep existing
                // Free the index we allocated
                let _ = self.index_allocator.free(our_index);

                info!(
                    node_addr = %peer_node_addr,
                    winner_link = %existing_link_id,
                    loser_link = %link_id,
                    "Cross-connection resolved: this connection lost"
                );

                Ok(PromotionResult::CrossConnectionLost {
                    winner_link_id: existing_link_id,
                })
            }
        } else {
            // No existing promoted peer. There may be a pending outbound
            // connection to the same peer (cross-connection in progress).
            // Do NOT clean it up yet — we need the outbound to stay alive
            // so that when the peer's msg2 arrives, we can learn the peer's
            // inbound session index and update their_index on the promoted
            // peer. The outbound will be cleaned up in handle_msg2 or by
            // the 30s handshake timeout.
            let pending_to_same_peer: Vec<LinkId> = self
                .connections
                .iter()
                .filter(|(_, conn)| {
                    conn.expected_identity()
                        .map(|id| *id.node_addr() == peer_node_addr)
                        .unwrap_or(false)
                })
                .map(|(lid, _)| *lid)
                .collect();

            for pending_link_id in &pending_to_same_peer {
                debug!(
                    node_addr = %peer_node_addr,
                    pending_link_id = %pending_link_id,
                    promoted_link_id = %link_id,
                    "Deferring cleanup of pending outbound (awaiting msg2 for index update)"
                );
            }

            // Normal promotion
            if self.max_peers > 0 && self.peers.len() >= self.max_peers {
                let _ = self.index_allocator.free(our_index);
                return Err(NodeError::MaxPeersExceeded { max: self.max_peers });
            }

            let mut new_peer = ActivePeer::with_session(
                verified_identity,
                link_id,
                current_time_ms,
                noise_session,
                our_index,
                their_index,
                transport_id,
                current_addr,
                link_stats,
                is_outbound,
                &self.config.node.mmp,
            );
            new_peer.set_tree_announce_min_interval_ms(self.config.node.tree.announce_min_interval_ms);

            self.peers.insert(peer_node_addr, new_peer);
            self.peers_by_index
                .insert((transport_id, our_index.as_u32()), peer_node_addr);
            self.retry_pending.remove(&peer_node_addr);
            self.register_identity(peer_node_addr, verified_identity.pubkey_full());

            info!(
                node_addr = %peer_node_addr,
                link_id = %link_id,
                our_index = %our_index,
                their_index = %their_index,
                "Connection promoted to active peer"
            );

            Ok(PromotionResult::Promoted(peer_node_addr))
        }
    }
}