Bugfix: recover from utreexo nodes hangup (#100)

If all our utreexo connections are lost, and we take too long to
recover, we might download blocks out-of-order and mess our acc up.
This commit makes sure blocks are accepted in only in order.

crates/floresta-chain/src/pruned_utreexo/chain_state.rs

@@ -927,6 +927,15 @@ impl<PersistedState: ChainStore> UpdatableChainstate for ChainState<PersistedSta
             | DiskBlockHeader::InvalidChain(_) => return Ok(0),
             DiskBlockHeader::HeadersOnly(_, height) => height,
         };
+
+        // Check if this block is the next one in our chain, if we try
+        // to add them out-of-order, we'll have consensus issues with our
+        // accumulator
+        let expected_height = self.get_validation_index()? + 1;
+        if height != expected_height {
+            return Ok(height);
+        }
+
         self.validate_block(block, height, inputs)?;
         let acc = Consensus::update_acc(&self.acc(), block, height, proof, del_hashes)?;
         let ibd = self.is_in_idb();

crates/floresta-chain/src/pruned_utreexo/chainstore.rs

@@ -170,7 +170,6 @@ impl ChainStore for KvChainStore {
         // Flush the default bucket with meta-info
         let bucket = self.0.bucket::<&[u8], Vec<u8>>(None)?;
         bucket.flush()?;
-
         Ok(())
     }
     fn save_header(&self, header: &DiskBlockHeader) -> Result<(), Self::Error> {

crates/floresta-wire/src/p2p_wire/node.rs

@@ -1111,6 +1111,7 @@ where
             {
                 try_and_log!(self.handle_notification(notification).await);
             }
+
             if *kill_signal.read().await {
                 self.shutdown().await;
                 break;
@@ -1324,6 +1325,14 @@ where
             return Err(WireError::PeerMisbehaving);
         }
 
+        let validation_index = self.chain.get_validation_index()?;
+        let validation_hash = self.chain.get_block_hash(validation_index)?;
+
+        // We've downloaded a block that's not the next we need, ignore it for now
+        if validation_hash != block.block.header.prev_blockhash {
+            return Ok(());
+        }
+
         let (proof, del_hashes, inputs) = Self::process_proof(
             &block.udata.unwrap(),
             &block.block.txdata,