Fix pruning BridgePool Merkle tree

.changelog/unreleased/bug-fixes/2264-fix-bp-tree-pruning.md

@@ -0,0 +1,2 @@
+- Fix to skip pruning BridgePool Merkle trees when no signed nonce
+  ([\#2264](https://github.com/anoma/namada/issues/2264))

apps/src/lib/node/ledger/storage/mod.rs

@@ -591,11 +591,8 @@ mod tests {
         );
         let new_epoch_start = BlockHeight(1);
         let signed_root_key = bridge_pool::get_signed_root_key();
+        // the first nonce isn't written for a test skipping pruning
         let nonce = Uint::default();
-        let root_proof =
-            BridgePoolRootProof::new((KeccakHash::default(), nonce));
-        let bytes = types::encode(&root_proof);
-        storage.write(&signed_root_key, bytes).unwrap();
 
         storage
             .begin_block(BlockHash::default(), new_epoch_start)
@@ -622,11 +619,8 @@ mod tests {
             .write(&key, types::encode(&value))
             .expect("write failed");
 
+        // the second nonce isn't written for a test skipping pruning
         let nonce = nonce + 1;
-        let root_proof =
-            BridgePoolRootProof::new((KeccakHash::default(), nonce));
-        let bytes = types::encode(&root_proof);
-        storage.write(&signed_root_key, bytes).unwrap();
 
         storage.block.epoch = storage.block.epoch.next();
         storage.block.pred_epochs.new_epoch(new_epoch_start);

apps/src/lib/node/ledger/storage/rocksdb.rs

@@ -1453,17 +1453,21 @@ impl DB for RocksDB {
         &self,
         height: BlockHeight,
         last_height: BlockHeight,
-    ) -> Result<Uint> {
+    ) -> Result<Option<Uint>> {
         let nonce_key = bridge_pool::get_signed_root_key();
         let bytes = if height == BlockHeight(0) || height >= last_height {
             self.read_subspace_val(&nonce_key)?
         } else {
             self.read_subspace_val_with_height(&nonce_key, height, last_height)?
         };
-        let bytes = bytes.expect("Signed root should exist");
-        let bp_root_proof = BridgePoolRootProof::try_from_slice(&bytes)
-            .map_err(Error::BorshCodingError)?;
-        Ok(bp_root_proof.data.1)
+        match bytes {
+            Some(bytes) => {
+                let bp_root_proof = BridgePoolRootProof::try_from_slice(&bytes)
+                    .map_err(Error::BorshCodingError)?;
+                Ok(Some(bp_root_proof.data.1))
+            }
+            None => Ok(None),
+        }
     }
 
     fn write_replay_protection_entry(

core/src/ledger/storage/mockdb.rs

@@ -593,8 +593,8 @@ impl DB for MockDB {
         &self,
         _height: BlockHeight,
         _last_height: BlockHeight,
-    ) -> Result<Uint> {
-        Ok(Uint::default())
+    ) -> Result<Option<Uint>> {
+        Ok(None)
     }
 
     fn write_replay_protection_entry(

core/src/ledger/storage/mod.rs

@@ -363,7 +363,7 @@ pub trait DB: std::fmt::Debug {
         &self,
         height: BlockHeight,
         last_height: BlockHeight,
-    ) -> Result<Uint>;
+    ) -> Result<Option<Uint>>;
 
     /// Write a replay protection entry
     fn write_replay_protection_entry(
@@ -1178,7 +1178,10 @@ where
             }
 
             // Prune the BridgePool subtree stores with invalid nonce
-            let mut epoch = self.get_oldest_epoch_with_valid_nonce()?;
+            let mut epoch = match self.get_oldest_epoch_with_valid_nonce()? {
+                Some(epoch) => epoch,
+                None => return Ok(()),
+            };
             while oldest_epoch < epoch {
                 epoch = epoch.prev();
                 self.db.prune_merkle_tree_store(
@@ -1216,11 +1219,15 @@ where
     }
 
     /// Get oldest epoch which has the valid signed nonce of the bridge pool
-    pub fn get_oldest_epoch_with_valid_nonce(&self) -> Result<Epoch> {
+    fn get_oldest_epoch_with_valid_nonce(&self) -> Result<Option<Epoch>> {
         let last_height = self.get_last_block_height();
-        let current_nonce = self
+        let current_nonce = match self
             .db
-            .read_bridge_pool_signed_nonce(last_height, last_height)?;
+            .read_bridge_pool_signed_nonce(last_height, last_height)?
+        {
+            Some(nonce) => nonce,
+            None => return Ok(None),
+        };
         let (mut epoch, _) = self.get_last_epoch();
         // We don't need to check the older epochs because their Merkle tree
         // snapshots have been already removed
@@ -1235,13 +1242,19 @@ where
                     Some(h) => h,
                     None => continue,
                 };
-            let nonce =
-                self.db.read_bridge_pool_signed_nonce(height, last_height)?;
+            let nonce = match self
+                .db
+                .read_bridge_pool_signed_nonce(height, last_height)?
+            {
+                Some(nonce) => nonce,
+                // skip pruning when the old epoch doesn't have the signed nonce
+                None => break,
+            };
             if nonce < current_nonce {
                 break;
             }
         }
-        Ok(epoch)
+        Ok(Some(epoch))
     }
 
     /// Check it the given transaction's hash is already present in storage