1 files changed, 83 insertions, 7 deletions

diff --git a/src/transport/identity.rs b/src/transport/identity.rs
index 0c4cda4..94faded 100644
--- a/src/transport/identity.rs
+++ b/src/transport/identity.rs
@@ -20,7 +20,9 @@
 //!   (`learn_addresses`): hints, not proofs. A message to a node goes to the addresses
 //!   it proved itself at, best first (`Paths::rank`, `Paths::send_first`: the next
 //!   when a send fails); with only hints, those are asked WHO, and the send is refused
-//!   until one answers (the node retries refused sends).
+//!   until one answers (the node retries refused sends). A node proven on some
+//!   transports is asked WHO at its hints on the others too, now and then
+//!   (`OTHER_PATHS_ASK_INTERVAL`), so that each transport both have becomes a path.
 //!
 //! Addresses and the transports behind them are the paths layer's
 //! (`transport::paths`): the books keep addresses as paths keep them.
@@ -50,6 +52,10 @@ pub(crate) const WHO_LABEL: &[u8] = b"continuum/who/1";
 pub(crate) const ME_LABEL: &[u8] = b"continuum/me/1";
 /// An address is asked WHO at most this often, unless a seed is being resolved.
 const ASK_INTERVAL: Duration = Duration::from_secs(5);
+/// A node's addresses on transports it hasn't proven itself on are asked WHO at most
+/// this often (`Book::unproven_hints`): over Tor, a WHO is a dial that takes seconds,
+/// and an address that doesn't answer shouldn't be pressed.
+const OTHER_PATHS_ASK_INTERVAL: Duration = Duration::from_secs(60);
 /// How long resolving a seed waits for its ME.
 const RESOLVE_TIMEOUT: Duration = Duration::from_secs(10);
 /// Addresses kept per node from hints: about one per transport.
@@ -190,19 +196,44 @@ impl Book {
         }
     }
 
+    /// Where `node` is said to be on transports it hasn't proven itself on yet.
+    fn unproven_hints(&self, node: &str) -> Vec<String> {
+        let proven = self.proven.get(node);
+        self.hints
+            .get(node)
+            .into_iter()
+            .flatten()
+            .filter(|hint| {
+                proven.is_none_or(|proven| {
+                    !proven
+                        .iter()
+                        .any(|address| scheme_of(address) == scheme_of(hint))
+                })
+            })
+            .cloned()
+            .collect()
+    }
+
     /// Whether to ask `address` WHO now (always, if `force`), noting that it was asked.
     fn ask(&mut self, address: &str, now: Instant, force: bool) -> bool {
-        if !force
-            && self
-                .asked
-                .get(address)
-                .is_some_and(|at| now.duration_since(*at) < ASK_INTERVAL)
+        let interval = if force { Duration::ZERO } else { ASK_INTERVAL };
+        self.ask_every(address, now, interval)
+    }
+
+    /// Whether to ask `address` WHO now, if it wasn't within `interval`, noting that it
+    /// was asked.
+    fn ask_every(&mut self, address: &str, now: Instant, interval: Duration) -> bool {
+        if self
+            .asked
+            .get(address)
+            .is_some_and(|at| now.duration_since(*at) < interval)
         {
             return false;
         }
         if self.asked.len() >= MAX_ENTRIES {
+            // The longest interval: other paths' asks are kept until they are due again.
             self.asked
-                .retain(|_, at| now.duration_since(*at) < ASK_INTERVAL);
+                .retain(|_, at| now.duration_since(*at) < OTHER_PATHS_ASK_INTERVAL);
         }
         self.asked.insert(address.to_owned(), now);
         true
@@ -301,6 +332,27 @@ impl Shared {
         if !self.lock().ask(address, Instant::now(), force) {
             return;
         }
+        self.send_who(address);
+    }
+
+    /// Asks `node`'s addresses on transports it hasn't proven itself on WHO, now and then
+    /// (`OTHER_PATHS_ASK_INTERVAL`): its ME there proves another path to it, which the
+    /// paths layer then measures, and fails over to.
+    fn ask_other_paths(self: &Arc<Self>, node: &str) {
+        let due: Vec<String> = {
+            let mut book = self.lock();
+            let now = Instant::now();
+            book.unproven_hints(node)
+                .into_iter()
+                .filter(|address| book.ask_every(address, now, OTHER_PATHS_ASK_INTERVAL))
+                .collect()
+        };
+        for address in due {
+            self.send_who(&address);
+        }
+    }
+
+    fn send_who(self: &Arc<Self>, address: &str) {
         let shared = Arc::clone(self);
         let address = address.to_owned();
         tokio::spawn(async move { shared.send_proof(MessageKind::Who, &address).await });
@@ -571,6 +623,9 @@ impl Transport for IdentityTransport {
     /// fails (`Paths::send_first`); refused if it proved itself nowhere yet.
     async fn send_encoded(&self, message: &EncodedMessage) -> Result<()> {
         let proven = self.shared.proven_at(&message.peer);
+        if !proven.is_empty() {
+            self.shared.ask_other_paths(&message.peer);
+        }
         if proven.is_empty() {
             let hints = {
                 let mut book = self.shared.lock();
@@ -652,6 +707,27 @@ mod tests {
     }
 
     #[test]
+    fn other_paths_are_the_hints_on_transports_not_proven() {
+        let now = Instant::now();
+        let mut book = Book::default();
+        book.hints
+            .insert("n1".into(), vec!["s:x".into(), "t:x".into(), "u:x".into()]);
+        // Proven nowhere: every hint.
+        assert_eq!(book.unproven_hints("n1"), ["s:x", "t:x", "u:x"]);
+        // Proven on s (even at another address): the others.
+        book.bind("s:y", "n1", now);
+        assert_eq!(book.unproven_hints("n1"), ["t:x", "u:x"]);
+        assert!(book.ask_every("t:x", now, OTHER_PATHS_ASK_INTERVAL));
+        assert!(!book.ask_every("t:x", now + ASK_INTERVAL, OTHER_PATHS_ASK_INTERVAL));
+        assert!(book.ask_every(
+            "t:x",
+            now + OTHER_PATHS_ASK_INTERVAL,
+            OTHER_PATHS_ASK_INTERVAL
+        ));
+        assert!(book.unproven_hints("n2").is_empty());
+    }
+
+    #[test]
     fn asking_is_rate_limited() {
         let now = Instant::now();
         let mut book = Book::default();