Add find_next_available_key function to prevent overwriting buckets

crates/lox-library/src/bridge_table.rs

@@ -255,14 +255,20 @@ pub struct BridgeTable {
     /// In some instances a single bridge may need to be added to a bucket
     /// In that case, a spare bucket will be removed from the set of spare bridges. One
     pub unallocated_bridges: Vec<BridgeLine>,
+    // To prevent issues with a counter for the hashmap keys, we keep a list of keys that
+    // no longer match any buckets that can be used before increasing the counter
+    pub recycleable_keys: Vec<u32>,
+    // We maintain a list of keys that have been blocked, as well as the date of their blocking
+    // so that they can be repurposed with new buckets eventually
+    pub blocked_keys: Vec<(u32, u32)>,
     /// The date the buckets were last encrypted to make the encbucket.
     /// The encbucket must be rebuilt each day so that the Bucket
     /// Reachability credentials in the buckets can be refreshed.
     pub date_last_enc: u32,
 }
 
-// Invariant: the lengths of the keys and buckets vectors are the same.
-// The encbuckets vector only gets updated when encrypt_table is called.
+// Invariant: the lengths of the keys and bucket hashmap are the same.
+// The encbuckets hashmap only gets updated when encrypt_table is called.
 
 impl BridgeTable {
     /// Get the number of buckets in the bridge table
@@ -270,6 +276,54 @@ impl BridgeTable {
         self.buckets.len()
     }
 
+    /// Get today's (real or simulated) date
+    fn today(&self) -> u32 {
+        // We will not encounter negative Julian dates (~6700 years ago)
+        // or ones larger than 32 bits
+        (time::OffsetDateTime::now_utc().date())
+            .to_julian_day()
+            .try_into()
+            .unwrap()
+    }
+
+    // Since buckets are moved around in the bridge_table, finding a lookup key that
+    // does not overwrite existing bridges could become an issue. We keep a list
+    // of recycleable lookup keys from buckets that have been removed and prioritize
+    // this list before increasing the counter
+    fn find_next_available_key(&mut self) -> u32 {
+        // First check if there are any blocked indexes that are old enough to be replaced
+        if !self.blocked_keys.is_empty()
+            && self.blocked_keys.iter().any(|&x| x.1 > self.today() + 30)
+        //Perhaps 30 should be changed to a later/earlier time
+        {
+            let blocked_keys_clone = self.blocked_keys.clone();
+            // If so, separate them from the fresh blockages
+            let (expired, fresh): (Vec<(u32, u32)>, Vec<(u32, u32)>) = blocked_keys_clone
+                .into_iter()
+                .partition(|&x| x.1 > self.today() + 30);
+            for item in expired {
+                let new_item = item.0;
+                //and add them to the recyclable keys
+                self.recycleable_keys.push(new_item);
+            }
+            // update the blocked_keys vector to only include the fresh keys
+            self.blocked_keys = fresh
+        }
+        if self.recycleable_keys.is_empty() {
+            let mut test_index = 1;
+            let mut test_counter = self.counter.wrapping_add(test_index);
+            while self.buckets.contains_key(&test_counter) {
+                for i in 0..5000 {
+                    test_index += i;
+                    test_counter = self.counter.wrapping_add(test_index);
+                }
+            }
+            self.counter = self.counter.wrapping_add(test_index);
+            self.counter
+        } else {
+            self.recycleable_keys.pop().unwrap()
+        }
+    }
     /// Append a new bucket to the bridge table, returning its index
     pub fn new_bucket(&mut self, bucket: &[BridgeLine; MAX_BRIDGES_PER_BUCKET]) -> u32 {
         // Pick a random key to encrypt this bucket
@@ -277,17 +331,18 @@ impl BridgeTable {
         let mut key: [u8; 16] = [0; 16];
         rng.fill_bytes(&mut key);
         // Increase the counter to identify the bucket, wrap value if beyond u32::MAX
-        self.counter = self.counter.wrapping_add(1);
-        self.keys.insert(self.counter, key);
-        self.buckets.insert(self.counter, *bucket);
+        let index = self.find_next_available_key();
+        //self.counter = self.counter.wrapping_add(1);
+        self.keys.insert(index, key);
+        self.buckets.insert(index, *bucket);
         // TODO: maybe we don't need this if the hashtable can keep track of available bridges
         // Mark the new bridges as available
         for (i, b) in bucket.iter().enumerate() {
             if b.port > 0 {
                 if let Some(v) = self.reachable.get_mut(b) {
-                    v.push((self.counter, i));
+                    v.push((index, i));
                 } else {
-                    let v = vec![(self.counter, i)];
+                    let v = vec![(index, i)];
                     self.reachable.insert(*b, v);
                 }
             }

crates/lox-library/src/lib.rs

@@ -445,6 +445,7 @@ impl BridgeAuth {
                     // Get the first spare and remove it from the spares set.
                     let spare = *self.bridge_table.spares.iter().next().unwrap();
                     self.bridge_table.spares.remove(&spare);
+                    self.bridge_table.recycleable_keys.push(spare);
                     // Get the actual bridges from the spare bucket
                     let spare_bucket = match self.bridge_table.buckets.remove(&spare) {
                         Some(spare_bucket) => spare_bucket,
@@ -567,6 +568,9 @@ impl BridgeAuth {
                         // set.
                         let spare = *self.bridge_table.spares.iter().next().unwrap();
                         self.bridge_table.spares.remove(&spare);
+                        self.bridge_table
+                            .blocked_keys
+                            .push((*bucketnum, self.today()));
                         // Add a blockage migration from this bucket to the spare
                         self.blockage_migration_table
                             .table