Implement RawIterator.seek_for_prev

librocksdb-sys/src/lib.rs

@@ -294,6 +294,8 @@ extern "C" {
 
     pub fn rocksdb_iter_seek(iterator: *mut rocksdb_iterator_t, k: *const c_char, klen: size_t);
 
+    pub fn rocksdb_iter_seek_for_prev(iterator: *mut rocksdb_iterator_t, k: *const c_char, klen: size_t);
+
     pub fn rocksdb_iter_next(iterator: *mut rocksdb_iterator_t);
 
     pub fn rocksdb_iter_prev(iterator: *mut rocksdb_iterator_t);

src/db.rs

@@ -135,6 +135,14 @@ pub struct Snapshot<'a> {
 ///     iter.next();
 /// }
 ///
+/// // Reverse iteration from key
+/// // Note, use seek_for_prev when reversing because if this key doesn't exist,
+/// // this will make the iterator start from the previous key rather than the next.
+/// iter.seek_for_prev(b"my key");
+/// while iter.valid() {
+///     println!("Saw {:?} {:?}", iter.key(), iter.value());
+///     iter.prev();
+/// }
 /// ```
 pub struct DBRawIterator {
     inner: *mut ffi::rocksdb_iterator_t,
@@ -307,9 +315,6 @@ impl DBRawIterator {
         unsafe { ffi::rocksdb_iter_seek(self.inner, key.as_ptr() as *const c_char, key.len() as size_t); }
     }
 
-/*
-    SeekForPrev was added in RocksDB 4.13 but not implemented in the C API until RocksDB 5.0
-
     /// Seeks to the specified key, or the first key that lexicographically precedes it.
     ///
     /// Like ``.seek()`` this method will attempt to seek to the specified key.
@@ -336,7 +341,6 @@ impl DBRawIterator {
     pub fn seek_for_prev(&mut self, key: &[u8]) {
         unsafe { ffi::rocksdb_iter_seek_for_prev(self.inner, key.as_ptr() as *const c_char, key.len() as size_t); }
     }
-*/
 
     /// Seeks to the next key.
     ///

tests/test_raw_iterator.rs

@@ -98,7 +98,6 @@ pub fn test_seek() {
     let db = setup_test_db("seek");
     db.put(b"k1", b"v1").unwrap();
     db.put(b"k2", b"v2").unwrap();
-    db.put(b"k3", b"v3").unwrap();
     db.put(b"k4", b"v4").unwrap();
 
     let mut iter = db.raw_iterator();
@@ -107,6 +106,13 @@ pub fn test_seek() {
     assert_eq!(iter.valid(), true);
     assert_eq!(iter.key(), Some(b"k2".to_vec()));
     assert_eq!(iter.value(), Some(b"v2".to_vec()));
+
+    // Check it gets the next key when the key doesn't exist
+    iter.seek(b"k3");
+
+    assert_eq!(iter.valid(), true);
+    assert_eq!(iter.key(), Some(b"k4".to_vec()));
+    assert_eq!(iter.value(), Some(b"v4".to_vec()));
 }
 
 
@@ -124,3 +130,25 @@ pub fn test_seek_to_nonexistant() {
     assert_eq!(iter.key(), Some(b"k3".to_vec()));
     assert_eq!(iter.value(), Some(b"v3".to_vec()));
 }
+
+#[test]
+pub fn test_seek_for_prev() {
+    let db = setup_test_db("seek_for_prev");
+    db.put(b"k1", b"v1").unwrap();
+    db.put(b"k2", b"v2").unwrap();
+    db.put(b"k4", b"v4").unwrap();
+
+    let mut iter = db.raw_iterator();
+    iter.seek(b"k2");
+
+    assert_eq!(iter.valid(), true);
+    assert_eq!(iter.key(), Some(b"k2".to_vec()));
+    assert_eq!(iter.value(), Some(b"v2".to_vec()));
+
+    // Check it gets the previous key when the key doesn't exist
+    iter.seek_for_prev(b"k3");
+
+    assert_eq!(iter.valid(), true);
+    assert_eq!(iter.key(), Some(b"k2".to_vec()));
+    assert_eq!(iter.value(), Some(b"v2".to_vec()));
+}