Add a check to ensure that blocks passed to `put_blocks` are sequential.

zcash_client_backend/src/data_api.rs

@@ -494,6 +494,8 @@ pub trait WalletWrite: WalletRead {
     /// Updates the state of the wallet database by persisting the provided block information,
     /// along with the note commitments that were detected when scanning the block for transactions
     /// pertaining to this wallet.
+    ///
+    /// `blocks` must be sequential, in order of increasing block height
     fn put_blocks(
         &mut self,
         block: Vec<ScannedBlock<sapling::Nullifier>>,

zcash_client_sqlite/src/error.rs

@@ -57,6 +57,9 @@ pub enum SqliteClientError {
     /// different hash. This indicates that a required rewind was not performed.
     BlockConflict(BlockHeight),
 
+    /// A range of blocks provided to the database as a unit was non-sequential
+    NonSequentialBlocks,
+
     /// A requested rewind would violate invariants of the storage layer. The payload returned with
     /// this error is (safe rewind height, requested height).
     RequestedRewindInvalid(BlockHeight, BlockHeight),
@@ -118,6 +121,7 @@ impl fmt::Display for SqliteClientError {
             SqliteClientError::Io(e) => write!(f, "{}", e),
             SqliteClientError::InvalidMemo(e) => write!(f, "{}", e),
             SqliteClientError::BlockConflict(h) => write!(f, "A block hash conflict occurred at height {}; rewind required.", u32::from(*h)),
+            SqliteClientError::NonSequentialBlocks => write!(f, "`put_blocks` requires that the provided block range be sequential"),
             SqliteClientError::DiversifierIndexOutOfRange => write!(f, "The space of available diversifier indices is exhausted"),
             SqliteClientError::KeyDerivationError(acct_id) => write!(f, "Key derivation failed for account {:?}", acct_id),
             SqliteClientError::AccountIdDiscontinuity => write!(f, "Wallet account identifiers must be sequential."),

zcash_client_sqlite/src/lib.rs

@@ -412,6 +412,10 @@ impl<P: consensus::Parameters> WalletWrite for WalletDb<rusqlite::Connection, P>
             let mut end_height = None;
 
             for block in blocks.into_iter() {
+                if end_height.iter().any(|prev| block.height() != *prev + 1) {
+                    return Err(SqliteClientError::NonSequentialBlocks);
+                }
+
                 // Insert the block into the database.
                 wallet::put_block(
                     wdb.conn.0,