1 files changed, 173 insertions, 0 deletions
diff --git a/src/advertise.rs b/src/advertise.rs
new file mode 100644
index 0000000..b415b5b
--- /dev/null
+++ b/src/advertise.rs
@@ -0,0 +1,173 @@
+//! Local address advertisement.
+//!
+//! Allows a node to announce its address to peers so
+//! they can update their routing tables with the correct
+//! endpoint.
+//!
+//! Used after NAT detection to inform peers of the
+//! node's externally-visible address.
+
+use std::collections::HashMap;
+use std::time::{Duration, Instant};
+
+use crate::id::NodeId;
+
+// ── Constants ────────────────────────────────────────
+
+/// TTL for advertisements.
+pub const ADVERTISE_TTL: Duration = Duration::from_secs(300);
+
+/// Timeout for a single advertisement attempt.
+pub const ADVERTISE_TIMEOUT: Duration = Duration::from_secs(2);
+
+/// Interval between refresh cycles.
+pub const ADVERTISE_REFRESH_INTERVAL: Duration = Duration::from_secs(100);
+
+/// A pending outgoing advertisement.
+#[derive(Debug)]
+struct PendingAd {
+    sent_at: Instant,
+}
+
+/// A received advertisement from a peer.
+#[derive(Debug)]
+struct ReceivedAd {
+    received_at: Instant,
+}
+
+/// Address advertisement manager.
+pub struct Advertise {
+    /// Pending outgoing advertisements by nonce.
+    pending: HashMap<u32, PendingAd>,
+
+    /// Received advertisements by peer ID.
+    received: HashMap<NodeId, ReceivedAd>,
+}
+
+impl Advertise {
+    pub fn new(_local_id: NodeId) -> Self {
+        Self {
+            pending: HashMap::new(),
+            received: HashMap::new(),
+        }
+    }
+
+    /// Start an advertisement to a peer.
+    ///
+    /// Returns the nonce to include in the message.
+    pub fn start_advertise(&mut self, nonce: u32) -> u32 {
+        self.pending.insert(
+            nonce,
+            PendingAd {
+                sent_at: Instant::now(),
+            },
+        );
+        nonce
+    }
+
+    /// Handle an advertisement reply (our ad was accepted).
+    ///
+    /// Returns `true` if the nonce matched a pending ad.
+    pub fn recv_reply(&mut self, nonce: u32) -> bool {
+        self.pending.remove(&nonce).is_some()
+    }
+
+    /// Handle an incoming advertisement from a peer.
+    ///
+    /// Records that this peer has advertised to us.
+    pub fn recv_advertise(&mut self, peer_id: NodeId) {
+        self.received.insert(
+            peer_id,
+            ReceivedAd {
+                received_at: Instant::now(),
+            },
+        );
+    }
+
+    /// Check if a peer has advertised to us recently.
+    pub fn has_advertised(&self, peer_id: &NodeId) -> bool {
+        self.received
+            .get(peer_id)
+            .map(|ad| ad.received_at.elapsed() < ADVERTISE_TTL)
+            .unwrap_or(false)
+    }
+
+    /// Remove expired pending ads and stale received ads.
+    pub fn refresh(&mut self) {
+        self.pending
+            .retain(|_, ad| ad.sent_at.elapsed() < ADVERTISE_TIMEOUT);
+        self.received
+            .retain(|_, ad| ad.received_at.elapsed() < ADVERTISE_TTL);
+    }
+
+    /// Number of pending outgoing advertisements.
+    pub fn pending_count(&self) -> usize {
+        self.pending.len()
+    }
+
+    /// Number of active received advertisements.
+    pub fn received_count(&self) -> usize {
+        self.received
+            .values()
+            .filter(|ad| ad.received_at.elapsed() < ADVERTISE_TTL)
+            .count()
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn advertise_and_reply() {
+        let mut adv = Advertise::new(NodeId::from_bytes([0x01; 32]));
+        adv.start_advertise(42);
+        assert_eq!(adv.pending_count(), 1);
+
+        assert!(adv.recv_reply(42));
+        assert_eq!(adv.pending_count(), 0);
+    }
+
+    #[test]
+    fn unknown_reply_ignored() {
+        let mut adv = Advertise::new(NodeId::from_bytes([0x01; 32]));
+        assert!(!adv.recv_reply(999));
+    }
+
+    #[test]
+    fn recv_advertisement() {
+        let mut adv = Advertise::new(NodeId::from_bytes([0x01; 32]));
+        let peer = NodeId::from_bytes([0x02; 32]);
+
+        assert!(!adv.has_advertised(&peer));
+        adv.recv_advertise(peer);
+        assert!(adv.has_advertised(&peer));
+        assert_eq!(adv.received_count(), 1);
+    }
+
+    #[test]
+    fn refresh_clears_stale() {
+        let mut adv = Advertise::new(NodeId::from_bytes([0x01; 32]));
+
+        // Insert already-expired pending ad
+        adv.pending.insert(
+            1,
+            PendingAd {
+                sent_at: Instant::now() - Duration::from_secs(10),
+            },
+        );
+
+        // Insert already-expired received ad
+        let peer = NodeId::from_bytes([0x02; 32]);
+        adv.received.insert(
+            peer,
+            ReceivedAd {
+                received_at: Instant::now() - Duration::from_secs(600),
+            },
+        );
+
+        adv.refresh();
+        assert_eq!(adv.pending_count(), 0);
+        assert_eq!(adv.received_count(), 0);
+    }
+}