bug(cursor_walk): handle empty range (#2057)

crates/storage/db/src/abstraction/cursor.rs

@@ -239,8 +239,6 @@ pub struct RangeWalker<'cursor, 'tx, T: Table, CURSOR: DbCursorRO<'tx, T>> {
     cursor: &'cursor mut CURSOR,
     /// `(key, value)` where to start the walk.
     start: IterPairResult<T>,
-    /// `key` where to start the walk.
-    start_key: Bound<T::Key>,
     /// `key` where to stop the walk.
     end_key: Bound<T::Key>,
     /// flag whether is ended
@@ -258,12 +256,9 @@ impl<'cursor, 'tx, T: Table, CURSOR: DbCursorRO<'tx, T>> std::iter::Iterator
             return None
         }
 
-        let start = self.start.take();
-        if start.is_some() && matches!(self.start_key, Bound::Included(_) | Bound::Unbounded) {
-            return start
-        }
+        let next_item = self.start.take().or_else(|| self.cursor.next().transpose());
 
-        match self.cursor.next().transpose() {
+        match next_item {
             Some(Ok((key, value))) => match &self.end_key {
                 Bound::Included(end_key) if &key <= end_key => Some(Ok((key, value))),
                 Bound::Excluded(end_key) if &key < end_key => Some(Ok((key, value))),
@@ -288,17 +283,19 @@ impl<'cursor, 'tx, T: Table, CURSOR: DbCursorRO<'tx, T>> RangeWalker<'cursor, 't
     pub fn new(
         cursor: &'cursor mut CURSOR,
         start: IterPairResult<T>,
-        start_key: Bound<T::Key>,
         end_key: Bound<T::Key>,
     ) -> Self {
-        Self {
-            cursor,
-            start,
-            start_key,
-            end_key,
-            is_done: false,
-            _tx_phantom: std::marker::PhantomData,
-        }
+        // mark done if range is empty.
+        let is_done = match start {
+            Some(Ok((ref start_key, _))) => match &end_key {
+                Bound::Included(end_key) if start_key > end_key => true,
+                Bound::Excluded(end_key) if start_key >= end_key => true,
+                _ => false,
+            },
+            None => true,
+            _ => false,
+        };
+        Self { cursor, start, end_key, is_done, _tx_phantom: std::marker::PhantomData }
     }
 }
 

crates/storage/db/src/implementation/mdbx/cursor.rs

@@ -94,12 +94,7 @@ impl<'tx, K: TransactionKind, T: Table> DbCursorRO<'tx, T> for Cursor<'tx, K, T>
         Self: Sized,
     {
         let start = match range.start_bound().cloned() {
-            Bound::Included(key) => {
-                if matches!(range.end_bound().cloned(), Bound::Included(end_key) | Bound::Excluded(end_key) if end_key < key) {
-                    return Err(Error::Read(2))
-                }
-                self.inner.set_range(key.encode().as_ref())
-            }
+            Bound::Included(key) => self.inner.set_range(key.encode().as_ref()),
             Bound::Excluded(_key) => {
                 unreachable!("Rust doesn't allow for Bound::Excluded in starting bounds");
             }
@@ -108,7 +103,7 @@ impl<'tx, K: TransactionKind, T: Table> DbCursorRO<'tx, T> for Cursor<'tx, K, T>
         .map_err(|e| Error::Read(e.into()))?
         .map(decoder::<T>);
 
-        Ok(RangeWalker::new(self, start, range.start_bound().cloned(), range.end_bound().cloned()))
+        Ok(RangeWalker::new(self, start, range.end_bound().cloned()))
     }
 
     fn walk_back<'cursor>(

crates/storage/db/src/implementation/mdbx/mod.rs

@@ -296,12 +296,16 @@ mod tests {
         let mut cursor = tx.cursor_read::<CanonicalHeaders>().unwrap();
 
         // start bound greater than end bound
-        let res = cursor.walk_range(3..1);
-        assert!(matches!(res, Err(Error::Read(2))));
+        let mut res = cursor.walk_range(3..1).unwrap();
+        assert_eq!(res.next(), None);
 
         // start bound greater than end bound
-        let res = cursor.walk_range(15..=2);
-        assert!(matches!(res, Err(Error::Read(2))));
+        let mut res = cursor.walk_range(15..=2).unwrap();
+        assert_eq!(res.next(), None);
+
+        // returning nothing
+        let mut walker = cursor.walk_range(1..1).unwrap();
+        assert_eq!(walker.next(), None);
     }
 
     #[test]

crates/storage/provider/src/transaction.rs

@@ -1621,7 +1621,7 @@ mod test {
         tx.insert_hashes(
             block1.number,
             exec_res1.transitions_count() as TransitionId,
-            exec_res2.transitions_count() as TransitionId,
+            (exec_res1.transitions_count() + exec_res2.transitions_count()) as TransitionId,
             2,
             block2.hash,
             block2.state_root,