Rename *rewind* to *truncate* in data_api methods.

This better reflects the semantics of wallet behavior. Also, this
adds a `zcash_client_backend::WalletRead::get_min_unspent_height`
method that replaces the deprecated & removed (and misleadingly
named) `get_rewind_height` method.

zcash_client_backend/CHANGELOG.md

@@ -9,6 +9,7 @@ and this library adheres to Rust's notion of
 ### Added
 - `data_api::SentTransactionOutput::from_parts`
 - `data_api::SentTransactionOutput::sapling_change_to`
+- `data_api::WalletRead::get_min_unspent_height`
 
 ### Changed
 - `decrypt::DecryptedOutput` is now parameterized by a `Note` type parameter,
@@ -25,6 +26,8 @@ and this library adheres to Rust's notion of
     data structure have been made private.
   - `WalletShieldedOutput` -> `WalletSaplingOutput`. Also, the internals of this
     data structure have been made private.
+- The `data_api::WalletWrite::rewind_to_height` method has been renamed to
+  `truncate_to_height` to better reflect its semantics.
 
 ### Removed
   - `wallet::WalletTx::num_spends`

zcash_client_backend/src/data_api.rs

@@ -83,6 +83,9 @@ pub trait WalletRead {
         })
     }
 
+    /// Returns the minimum block height corresponding to an unspent note in the wallet.
+    fn get_min_unspent_height(&self) -> Result<Option<BlockHeight>, Self::Error>;
+
     /// Returns the block hash for the block at the given height, if the
     /// associated block data is available. Returns `Ok(None)` if the hash
     /// is not found in the database.
@@ -361,7 +364,7 @@ pub trait WalletWrite: WalletRead {
     /// persistent wallet store.
     fn store_sent_tx(&mut self, sent_tx: &SentTransaction) -> Result<Self::TxRef, Self::Error>;
 
-    /// Rewinds the wallet database to the specified height.
+    /// Truncates the wallet database to the specified height.
     ///
     /// This method assumes that the state of the underlying data store is
     /// consistent up to a particular block height. Since it is possible that
@@ -373,8 +376,8 @@ pub trait WalletWrite: WalletRead {
     /// most recent block and all other operations will treat this block
     /// as the chain tip for balance determination purposes.
     ///
-    /// There may be restrictions on how far it is possible to rewind.
+    /// There may be restrictions on heights to which it is possible to truncate.
-    fn rewind_to_height(&mut self, block_height: BlockHeight) -> Result<(), Self::Error>;
+    fn truncate_to_height(&mut self, block_height: BlockHeight) -> Result<(), Self::Error>;
 
     /// Adds a transparent UTXO received by the wallet to the data store.
     fn put_received_transparent_utxo(
@@ -423,6 +426,10 @@ pub mod testing {
             Ok(None)
         }
 
+        fn get_min_unspent_height(&self) -> Result<Option<BlockHeight>, Self::Error> {
+            Ok(None)
+        }
+
         fn get_block_hash(
             &self,
             _block_height: BlockHeight,
@@ -588,7 +595,7 @@ pub mod testing {
             Ok(TxId::from_bytes([0u8; 32]))
         }
 
-        fn rewind_to_height(&mut self, _block_height: BlockHeight) -> Result<(), Self::Error> {
+        fn truncate_to_height(&mut self, _block_height: BlockHeight) -> Result<(), Self::Error> {
             Ok(())
         }
 

zcash_client_backend/src/data_api/chain.rs

@@ -55,7 +55,7 @@
 //!             let rewind_height = e.at_height() - 10;
 //!
 //!             // b) Rewind scanned block information.
-//!             db_data.rewind_to_height(rewind_height);
+//!             db_data.truncate_to_height(rewind_height);
 //!
 //!             // c) Delete cached blocks from rewind_height onwards.
 //!             //

zcash_client_sqlite/src/chain.rs

@@ -141,7 +141,7 @@ pub(crate) fn blockmetadb_insert(
 }
 
 #[cfg(feature = "unstable")]
-pub(crate) fn blockmetadb_rewind_to_height(
+pub(crate) fn blockmetadb_truncate_to_height(
     conn: &Connection,
     block_height: BlockHeight,
 ) -> Result<(), rusqlite::Error> {
@@ -284,7 +284,7 @@ mod tests {
             self, fake_compact_block, fake_compact_block_spending, init_test_accounts_table,
             insert_into_cache, sapling_activation_height, AddressType,
         },
-        wallet::{get_balance, init::init_wallet_db, rewind_to_height},
+        wallet::{get_balance, init::init_wallet_db, truncate_to_height},
         AccountId, BlockDb, WalletDb,
     };
 
@@ -479,7 +479,7 @@ mod tests {
     }
 
     #[test]
-    fn data_db_rewinding() {
+    fn data_db_truncation() {
         let cache_file = NamedTempFile::new().unwrap();
         let db_cache = BlockDb::for_path(cache_file.path()).unwrap();
         init_cache_database(&db_cache).unwrap();
@@ -529,7 +529,7 @@ mod tests {
         );
 
         // "Rewind" to height of last scanned block
-        rewind_to_height(&db_data, sapling_activation_height() + 1).unwrap();
+        truncate_to_height(&db_data, sapling_activation_height() + 1).unwrap();
 
         // Account balance should be unaltered
         assert_eq!(
@@ -538,7 +538,7 @@ mod tests {
         );
 
         // Rewind so that one block is dropped
-        rewind_to_height(&db_data, sapling_activation_height()).unwrap();
+        truncate_to_height(&db_data, sapling_activation_height()).unwrap();
 
         // Account balance should only contain the first received note
         assert_eq!(get_balance(&db_data, AccountId::from(0)).unwrap(), value);

zcash_client_sqlite/src/lib.rs

@@ -139,6 +139,10 @@ impl<P: consensus::Parameters> WalletRead for WalletDb<P> {
         wallet::block_height_extrema(self).map_err(SqliteClientError::from)
     }
 
+    fn get_min_unspent_height(&self) -> Result<Option<BlockHeight>, Self::Error> {
+        wallet::get_min_unspent_height(self).map_err(SqliteClientError::from)
+    }
+
     fn get_block_hash(&self, block_height: BlockHeight) -> Result<Option<BlockHash>, Self::Error> {
         wallet::get_block_hash(self, block_height).map_err(SqliteClientError::from)
     }
@@ -294,6 +298,10 @@ impl<'a, P: consensus::Parameters> WalletRead for DataConnStmtCache<'a, P> {
         self.wallet_db.block_height_extrema()
     }
 
+    fn get_min_unspent_height(&self) -> Result<Option<BlockHeight>, Self::Error> {
+        self.wallet_db.get_min_unspent_height()
+    }
+
     fn get_block_hash(&self, block_height: BlockHeight) -> Result<Option<BlockHash>, Self::Error> {
         self.wallet_db.get_block_hash(block_height)
     }
@@ -675,8 +683,8 @@ impl<'a, P: consensus::Parameters> WalletWrite for DataConnStmtCache<'a, P> {
         })
     }
 
-    fn rewind_to_height(&mut self, block_height: BlockHeight) -> Result<(), Self::Error> {
+    fn truncate_to_height(&mut self, block_height: BlockHeight) -> Result<(), Self::Error> {
-        wallet::rewind_to_height(self.wallet_db, block_height)
+        wallet::truncate_to_height(self.wallet_db, block_height)
     }
 
     fn put_received_transparent_utxo(
@@ -875,8 +883,8 @@ impl FsBlockDb {
     /// If the requested height is greater than or equal to the height
     /// of the last scanned block, or if the DB is empty, this function
     /// does nothing.
-    pub fn rewind_to_height(&self, block_height: BlockHeight) -> Result<(), FsBlockDbError> {
+    pub fn truncate_to_height(&self, block_height: BlockHeight) -> Result<(), FsBlockDbError> {
-        Ok(chain::blockmetadb_rewind_to_height(
+        Ok(chain::blockmetadb_truncate_to_height(
             &self.conn,
             block_height,
         )?)
@@ -1363,7 +1371,9 @@ mod tests {
         assert_eq!(db_meta.find_block(BlockHeight::from_u32(3)).unwrap(), None);
 
         // Rewinding to height 1 should cause the metadata for height 2 to be deleted.
-        db_meta.rewind_to_height(BlockHeight::from_u32(1)).unwrap();
+        db_meta
+            .truncate_to_height(BlockHeight::from_u32(1))
+            .unwrap();
         assert_eq!(
             db_meta.get_max_cached_height().unwrap(),
             Some(BlockHeight::from_u32(1)),

zcash_client_sqlite/src/wallet.rs

@@ -583,9 +583,9 @@ pub(crate) fn get_block_hash<P>(
         .optional()
 }
 
-/// Gets the height to which the database must be rewound if any rewind greater than the pruning
+/// Gets the height to which the database must be truncated if any truncation that would remove a
-/// height is attempted.
+/// number of blocks greater than the pruning height is attempted.
-pub(crate) fn get_rewind_height<P>(
+pub(crate) fn get_min_unspent_height<P>(
     wdb: &WalletDb<P>,
 ) -> Result<Option<BlockHeight>, SqliteClientError> {
     wdb.conn
@@ -603,13 +603,13 @@ pub(crate) fn get_rewind_height<P>(
         .map_err(SqliteClientError::from)
 }
 
-/// Rewinds the database to the given height.
+/// Truncates the database to the given height.
 ///
 /// If the requested height is greater than or equal to the height of the last scanned
 /// block, this function does nothing.
 ///
 /// This should only be executed inside a transactional context.
-pub(crate) fn rewind_to_height<P: consensus::Parameters>(
+pub(crate) fn truncate_to_height<P: consensus::Parameters>(
     wdb: &WalletDb<P>,
     block_height: BlockHeight,
 ) -> Result<(), SqliteClientError> {
@@ -628,7 +628,7 @@ pub(crate) fn rewind_to_height<P: consensus::Parameters>(
         })?;
 
     if block_height < last_scanned_height - PRUNING_HEIGHT {
-        if let Some(h) = get_rewind_height(wdb)? {
+        if let Some(h) = get_min_unspent_height(wdb)? {
             if block_height > h {
                 return Err(SqliteClientError::RequestedRewindInvalid(h, block_height));
             }