fix: header sync must allow transition to archival/pruned if tip is b…

…ehind (#3520)

Description
---
- Changes header sync to check the metadata height as there is still one case where it is valid for peers to enter header sync when all headers are synced
- Use last chain header instead of tip chain header when determining header sync state

Motivation and Context
---
Node would ban peer when headers are synced and sync is being resumed 

How Has This Been Tested?
---
Manually - header sync does not ban peer in this case

base_layer/core/src/base_node/sync/header_sync/synchronizer.rs

@@ -246,22 +246,37 @@ impl<'a, B: BlockchainBackend + 'static> HeaderSynchronizer<'a, B> {
         );
 
         // Fetch the local tip header at the beginning of the sync process
-        let local_tip_header = self.db.fetch_tip_header().await?;
+        let local_tip_header = self.db.fetch_last_chain_header().await?;
         let local_total_accumulated_difficulty = local_tip_header.accumulated_data().total_accumulated_difficulty;
+        let header_tip_height = local_tip_header.height();
         let sync_status = self
             .determine_sync_status(sync_peer, local_tip_header, &mut client)
             .await?;
         match sync_status {
-            SyncStatus::InSync => Err(BlockHeaderSyncError::PeerSentInaccurateChainMetadata {
-                claimed: sync_peer.claimed_chain_metadata().accumulated_difficulty(),
-                actual: None,
-                local: local_total_accumulated_difficulty,
-            }),
-            SyncStatus::WereAhead => Err(BlockHeaderSyncError::PeerSentInaccurateChainMetadata {
-                claimed: sync_peer.claimed_chain_metadata().accumulated_difficulty(),
-                actual: None,
-                local: local_total_accumulated_difficulty,
-            }),
+            SyncStatus::InSync | SyncStatus::WereAhead => {
+                let metadata = self.db.get_chain_metadata().await?;
+                if metadata.height_of_longest_chain() < header_tip_height {
+                    debug!(
+                        target: LOG_TARGET,
+                        "Headers are in sync at height {} but tip is {}. Proceeding to archival/pruned block sync",
+                        header_tip_height,
+                        metadata.height_of_longest_chain()
+                    );
+                    Ok(())
+                } else {
+                    debug!(
+                        target: LOG_TARGET,
+                        "Headers and block state are already in-sync (Header Tip: {}, Block tip: {})",
+                        header_tip_height,
+                        metadata.height_of_longest_chain()
+                    );
+                    Err(BlockHeaderSyncError::PeerSentInaccurateChainMetadata {
+                        claimed: sync_peer.claimed_chain_metadata().accumulated_difficulty(),
+                        actual: None,
+                        local: local_total_accumulated_difficulty,
+                    })
+                }
+            },
             SyncStatus::Lagging(split_info) => {
                 self.hooks.call_on_progress_header_hooks(
                     split_info.local_tip_header.height(),

base_layer/core/src/chain_storage/async_db.rs

@@ -195,6 +195,8 @@ impl<B: BlockchainBackend + 'static> AsyncBlockchainDb<B> {
 
     make_async_fn!(fetch_last_header() -> BlockHeader, "fetch_last_header");
 
+    make_async_fn!(fetch_last_chain_header() -> ChainHeader, "fetch_last_chain_header");
+
     make_async_fn!(fetch_tip_header() -> ChainHeader, "fetch_tip_header");
 
     make_async_fn!(insert_valid_headers(headers: Vec<ChainHeader>) -> (), "insert_valid_headers");

base_layer/core/src/chain_storage/blockchain_backend.rs

@@ -133,6 +133,8 @@ pub trait BlockchainBackend: Send + Sync {
     fn orphan_count(&self) -> Result<usize, ChainStorageError>;
     /// Returns the stored header with the highest corresponding height.
     fn fetch_last_header(&self) -> Result<BlockHeader, ChainStorageError>;
+    /// Returns the stored header and accumulated data with the highest height.
+    fn fetch_last_chain_header(&self) -> Result<ChainHeader, ChainStorageError>;
     /// Returns the stored header with the highest corresponding height.
     fn fetch_tip_header(&self) -> Result<ChainHeader, ChainStorageError>;
     /// Returns the stored chain metadata.

base_layer/core/src/chain_storage/blockchain_database.rs

@@ -566,6 +566,11 @@ where B: BlockchainBackend
         db.fetch_last_header()
     }
 
+    pub fn fetch_last_chain_header(&self) -> Result<ChainHeader, ChainStorageError> {
+        let db = self.db_read_access()?;
+        db.fetch_last_chain_header()
+    }
+
     /// Returns the sum of all kernels
     pub fn fetch_kernel_commitment_sum(&self, at_hash: &HashOutput) -> Result<Commitment, ChainStorageError> {
         Ok(self.fetch_block_accumulated_data(at_hash.clone())?.kernel_sum)

base_layer/core/src/chain_storage/lmdb_db/lmdb_db.rs

@@ -1942,6 +1942,31 @@ impl BlockchainBackend for LMDBDatabase {
         })
     }
 
+    /// Finds and returns the last stored header.
+    fn fetch_last_chain_header(&self) -> Result<ChainHeader, ChainStorageError> {
+        let txn = self.read_transaction()?;
+        let header = self.fetch_last_header_in_txn(&txn)?.ok_or_else(|| {
+            ChainStorageError::InvalidOperation("Cannot fetch last header because database is empty".to_string())
+        })?;
+        let height = header.height;
+        let accumulated_data = self
+            .fetch_header_accumulated_data_by_height(&txn, height)?
+            .ok_or_else(|| ChainStorageError::ValueNotFound {
+                entity: "BlockHeaderAccumulatedData",
+                field: "height",
+                value: height.to_string(),
+            })?;
+
+        let chain_header = ChainHeader::try_construct(header, accumulated_data).ok_or_else(|| {
+            ChainStorageError::DataInconsistencyDetected {
+                function: "fetch_tip_header",
+                details: format!("Accumulated data mismatch at height #{}", height),
+            }
+        })?;
+
+        Ok(chain_header)
+    }
+
     fn fetch_tip_header(&self) -> Result<ChainHeader, ChainStorageError> {
         let txn = self.read_transaction()?;
 

base_layer/core/src/test_helpers/blockchain.rs

@@ -314,6 +314,10 @@ impl BlockchainBackend for TempDatabase {
         self.db.as_ref().unwrap().fetch_last_header()
     }
 
+    fn fetch_last_chain_header(&self) -> Result<ChainHeader, ChainStorageError> {
+        self.db.as_ref().unwrap().fetch_last_chain_header()
+    }
+
     fn fetch_tip_header(&self) -> Result<ChainHeader, ChainStorageError> {
         self.db.as_ref().unwrap().fetch_tip_header()
     }