[#751] add support for rewind_to_height to FsBlockDb

Closes #751

Ran `cargo fmt`

return the result as an error rather than unwrap

Co-authored-by: Kris Nuttycombe <kris@nutty.land>

zcash_client_sqlite/CHANGELOG.md

@@ -6,7 +6,13 @@ and this library adheres to Rust's notion of
 [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
 ## [Unreleased]
-
+### Added 
+- `zcash_client_sqlite::FsBlockDb::rewind_to_height` rewinds the BlockMeta Db
+ to the specified height following the same logic as homonymous functions on 
+ `WalletDb`. This function does not delete the files referenced by the rows
+ that might be present and are deleted by this function call.
+- `zcash_client_sqlite::chain::blockmetadb_rewind_to_height` implementation
+ of the function above.
 ## [0.4.2] - 2022-12-13
 ### Fixed
 - `zcash_client_sqlite::WalletDb::get_transparent_balances` no longer returns an

zcash_client_sqlite/src/chain.rs

@@ -139,6 +139,16 @@ pub(crate) fn blockmetadb_insert(
     }
 }
 
+#[cfg(feature = "unstable")]
+pub(crate) fn blockmetadb_rewind_to_height(
+    conn: &Connection,
+    block_height: BlockHeight,
+) -> Result<(), rusqlite::Error> {
+    conn.prepare("DELETE FROM compactblocks_meta WHERE height > ?")?
+        .execute(params![u32::from(block_height)])?;
+    Ok(())
+}
+
 #[cfg(feature = "unstable")]
 pub(crate) fn blockmetadb_get_max_cached_height(
     conn: &Connection,

zcash_client_sqlite/src/lib.rs

@@ -929,6 +929,20 @@ impl FsBlockDb {
 
         Ok(chain::blockmetadb_insert(&self.conn, block_meta)?)
     }
+    /// Rewinds the BlockMeta Db to the `block_height` provided.
+    ///
+    /// This doesn't delete any files referenced by the records
+    /// stored in BlockMeta.
+    ///
+    /// 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> {
+        Ok(chain::blockmetadb_rewind_to_height(
+            &self.conn,
+            block_height,
+        )?)
+    }
 }
 
 #[cfg(feature = "unstable")]