address_store: Improve address tracking and add eviction algorithm

src/transport/manager/address.rs

@@ -18,12 +18,29 @@
 // FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
 // DEALINGS IN THE SOFTWARE.
 
-use crate::{types::ConnectionId, PeerId};
+use crate::{error::DialError, types::ConnectionId, PeerId};
 
 use multiaddr::{Multiaddr, Protocol};
 use multihash::Multihash;
 
-use std::collections::{BinaryHeap, HashSet};
+use std::collections::{hash_map::Entry, HashMap};
+
+/// Maximum number of addresses tracked for a peer.
+const MAX_ADDRESSES: usize = 64;
+
+/// Scores for address records.
+pub mod scores {
+    /// Score indicating that the connection was successfully established.
+    pub const CONNECTION_ESTABLISHED: i32 = 100i32;
+
+    /// Score for failing to connect due to an invalid or unreachable address.
+    pub const CONNECTION_FAILURE: i32 = -100i32;
+
+    /// Score for providing an invalid address.
+    ///
+    /// This address can never be reached.
+    pub const ADDRESS_FAILURE: i32 = i32::MIN;
+}
 
 #[allow(clippy::derived_hash_with_manual_eq)]
 #[derive(Debug, Clone, Hash)]
@@ -134,11 +151,10 @@ impl Ord for AddressRecord {
 /// Store for peer addresses.
 #[derive(Debug)]
 pub struct AddressStore {
-    //// Addresses sorted by score.
-    pub by_score: BinaryHeap<AddressRecord>,
-
-    /// Addresses queryable by hashing them for faster lookup.
-    pub by_address: HashSet<Multiaddr>,
+    /// Addresses available.
+    pub addresses: HashMap<Multiaddr, AddressRecord>,
+    /// Maximum capacity of the address store.
+    max_capacity: usize,
 }
 
 impl FromIterator<Multiaddr> for AddressStore {
@@ -158,8 +174,7 @@ impl FromIterator<AddressRecord> for AddressStore {
     fn from_iter<T: IntoIterator<Item = AddressRecord>>(iter: T) -> Self {
         let mut store = AddressStore::new();
         for record in iter {
-            store.by_address.insert(record.address.clone());
-            store.by_score.push(record);
+            store.insert(record);
         }
 
         store
@@ -186,52 +201,65 @@ impl AddressStore {
     /// Create new [`AddressStore`].
     pub fn new() -> Self {
         Self {
-            by_score: BinaryHeap::new(),
-            by_address: HashSet::new(),
+            addresses: HashMap::with_capacity(MAX_ADDRESSES),
+            max_capacity: MAX_ADDRESSES,
         }
     }
 
-    /// Check if [`AddressStore`] is empty.
-    pub fn is_empty(&self) -> bool {
-        self.by_score.is_empty()
+    /// Get the score for a given error.
+    pub fn error_score(error: &DialError) -> i32 {
+        match error {
+            DialError::AddressError(_) => scores::ADDRESS_FAILURE,
+            _ => scores::CONNECTION_FAILURE,
+        }
     }
 
-    /// Check if address is already in the a
-    pub fn contains(&self, address: &Multiaddr) -> bool {
-        self.by_address.contains(address)
+    /// Check if [`AddressStore`] is empty.
+    pub fn is_empty(&self) -> bool {
+        self.addresses.is_empty()
     }
 
-    /// Insert new address record into [`AddressStore`] with default address score.
-    pub fn insert(&mut self, mut record: AddressRecord) {
-        if self.by_address.contains(record.address()) {
+    /// Insert the address record into [`AddressStore`] with the provided score.
+    ///
+    /// If the address is not in the store, it will be inserted.
+    /// Otherwise, the score and connection ID will be updated.
+    pub fn insert(&mut self, record: AddressRecord) {
+        if let Entry::Occupied(mut occupied) = self.addresses.entry(record.address.clone()) {
+            occupied.get_mut().update_score(record.score);
             return;
         }
 
-        record.connection_id = None;
-        self.by_address.insert(record.address.clone());
-        self.by_score.push(record);
-    }
-
-    /// Pop address with the highest score from [`AddressStore`].
-    pub fn pop(&mut self) -> Option<AddressRecord> {
-        self.by_score.pop().map(|record| {
-            self.by_address.remove(&record.address);
-            record
-        })
-    }
-
-    /// Take at most `limit` `AddressRecord`s from [`AddressStore`].
-    pub fn take(&mut self, limit: usize) -> Vec<AddressRecord> {
-        let mut records = Vec::new();
-
-        for _ in 0..limit {
-            match self.pop() {
-                Some(record) => records.push(record),
-                None => break,
+        // The eviction algorithm favours addresses with higher scores.
+        //
+        // This algorithm has the following implications:
+        //  - it keeps the best addresses in the store.
+        //  - if the store is at capacity, the worst address will be evicted.
+        //  - an address that is not dialed yet (with score zero) will be preferred over an address
+        //  that already failed (with negative score).
+        if self.addresses.len() >= self.max_capacity {
+            let min_record = self
+                .addresses
+                .values()
+                .min()
+                .cloned()
+                .expect("There is at least one element checked above; qed");
+
+            // The lowest score is better than the new record.
+            if record.score < min_record.score {
+                return;
             }
+            self.addresses.remove(min_record.address());
         }
 
-        records
+        // Insert the record.
+        self.addresses.insert(record.address.clone(), record);
+    }
+
+    /// Return the available addresses sorted by score.
+    pub fn addresses(&self, limit: usize) -> Vec<Multiaddr> {
+        let mut records = self.addresses.values().cloned().collect::<Vec<_>>();
+        records.sort_by(|lhs, rhs| rhs.score.cmp(&lhs.score));
+        records.into_iter().take(limit).map(|record| record.address).collect()
     }
 }
 
@@ -256,7 +284,7 @@ mod tests {
             ),
             rng.gen_range(1..=65535),
         ));
-        let score: i32 = rng.gen();
+        let score: i32 = rng.gen_range(10..=200);
 
         AddressRecord::new(
             &peer,
@@ -279,7 +307,7 @@ mod tests {
             ),
             rng.gen_range(1..=65535),
         ));
-        let score: i32 = rng.gen();
+        let score: i32 = rng.gen_range(10..=200);
 
         AddressRecord::new(
             &peer,
@@ -303,7 +331,7 @@ mod tests {
             ),
             rng.gen_range(1..=65535),
         ));
-        let score: i32 = rng.gen();
+        let score: i32 = rng.gen_range(10..=200);
 
         AddressRecord::new(
             &peer,
@@ -331,19 +359,22 @@ mod tests {
             store.insert(quic_address_record(&mut rng));
         }
 
-        let known_addresses = store.by_address.len();
+        let known_addresses = store.addresses.len();
         assert!(known_addresses >= 3);
 
-        let taken = store.take(known_addresses - 2);
+        let taken = store.addresses(known_addresses - 2);
         assert_eq!(known_addresses - 2, taken.len());
         assert!(!store.is_empty());
 
         let mut prev: Option<AddressRecord> = None;
-        for record in taken {
-            assert!(!store.contains(record.address()));
+        for address in taken {
+            // Addresses are still in the store.
+            assert!(store.addresses.contains_key(&address));
+
+            let record = store.addresses.get(&address).unwrap().clone();
 
             if let Some(previous) = prev {
-                assert!(previous.score > record.score);
+                assert!(previous.score >= record.score);
             }
 
             prev = Some(record);
@@ -359,18 +390,19 @@ mod tests {
         store.insert(ws_address_record(&mut rng));
         store.insert(quic_address_record(&mut rng));
 
-        assert_eq!(store.by_address.len(), 3);
+        assert_eq!(store.addresses.len(), 3);
 
-        let taken = store.take(8usize);
+        let taken = store.addresses(8usize);
         assert_eq!(taken.len(), 3);
-        assert!(store.is_empty());
 
         let mut prev: Option<AddressRecord> = None;
         for record in taken {
+            let record = store.addresses.get(&record).unwrap().clone();
+
             if prev.is_none() {
                 prev = Some(record);
             } else {
-                assert!(prev.unwrap().score > record.score);
+                assert!(prev.unwrap().score >= record.score);
                 prev = Some(record);
             }
         }
@@ -401,10 +433,9 @@ mod tests {
             .collect::<HashMap<_, _>>();
         store.extend(records);
 
-        for record in store.by_score {
+        for record in store.addresses.values().cloned() {
             let stored = cloned.get(record.address()).unwrap();
             assert_eq!(stored.score(), record.score());
-            assert_eq!(stored.connection_id(), record.connection_id());
             assert_eq!(stored.address(), record.address());
         }
     }
@@ -433,11 +464,68 @@ mod tests {
         let cloned = records.iter().cloned().collect::<HashMap<_, _>>();
         store.extend(records.iter().map(|(_, record)| record));
 
-        for record in store.by_score {
+        for record in store.addresses.values().cloned() {
             let stored = cloned.get(record.address()).unwrap();
             assert_eq!(stored.score(), record.score());
-            assert_eq!(stored.connection_id(), record.connection_id());
             assert_eq!(stored.address(), record.address());
         }
     }
+
+    #[test]
+    fn insert_record() {
+        let mut store = AddressStore::new();
+        let mut rng = rand::thread_rng();
+
+        let mut record = tcp_address_record(&mut rng);
+        record.score = 10;
+
+        store.insert(record.clone());
+
+        assert_eq!(store.addresses.len(), 1);
+        assert_eq!(store.addresses.get(record.address()).unwrap(), &record);
+
+        // This time the record is updated.
+        store.insert(record.clone());
+
+        assert_eq!(store.addresses.len(), 1);
+        let store_record = store.addresses.get(record.address()).unwrap();
+        assert_eq!(store_record.score, record.score * 2);
+    }
+
+    #[test]
+    fn evict_on_capacity() {
+        let mut store = AddressStore {
+            addresses: HashMap::new(),
+            max_capacity: 2,
+        };
+
+        let mut rng = rand::thread_rng();
+        let mut first_record = tcp_address_record(&mut rng);
+        first_record.score = scores::CONNECTION_ESTABLISHED;
+        let mut second_record = ws_address_record(&mut rng);
+        second_record.score = 0;
+
+        store.insert(first_record.clone());
+        store.insert(second_record.clone());
+
+        assert_eq!(store.addresses.len(), 2);
+
+        // We have better addresses, ignore this one.
+        let mut third_record = quic_address_record(&mut rng);
+        third_record.score = scores::CONNECTION_FAILURE;
+        store.insert(third_record.clone());
+        assert_eq!(store.addresses.len(), 2);
+        assert!(store.addresses.contains_key(first_record.address()));
+        assert!(store.addresses.contains_key(second_record.address()));
+
+        // Evict the address with the lowest score.
+        // Store contains scores: [100, 0].
+        let mut fourth_record = quic_address_record(&mut rng);
+        fourth_record.score = 1;
+        store.insert(fourth_record.clone());
+
+        assert_eq!(store.addresses.len(), 2);
+        assert!(store.addresses.contains_key(first_record.address()));
+        assert!(store.addresses.contains_key(fourth_record.address()));
+    }
 }