add SetIterateLowerBound and testcase

Author: houfazhou

iterator_test.go

@@ -29,3 +29,36 @@ func TestIterator(t *testing.T) {
 	ensure.Nil(t, iter.Err())
 	ensure.DeepEqual(t, actualKeys, givenKeys)
 }
+
+func TestIteratorWithRange(t *testing.T) {
+	db := newTestDB(t, "TestIterator", nil)
+	defer db.Close()
+
+	// insert keys
+	givenKeys := [][]byte{
+		[]byte("key1"),
+		[]byte("key2"),
+		[]byte("key3"),
+		[]byte("key4"),
+		[]byte("key5"),
+	}
+	wo := NewDefaultWriteOptions()
+	for _, k := range givenKeys {
+		ensure.Nil(t, db.Put(wo, k, []byte("val")))
+	}
+
+	ro := NewDefaultReadOptions()
+	ro.SetIterateLowerBound([]byte("key2"))
+	ro.SetIterateUpperBound([]byte("key4"))
+
+	iter := db.NewIterator(ro)
+	defer iter.Close()
+	var actualKeys [][]byte
+	for iter.SeekToFirst(); iter.Valid(); iter.Next() {
+		key := make([]byte, 4)
+		copy(key, iter.Key().Data())
+		actualKeys = append(actualKeys, key)
+	}
+	ensure.Nil(t, iter.Err())
+	ensure.DeepEqual(t, len(actualKeys), 2)
+}

options_read.go

@@ -100,15 +100,29 @@ func (opts *ReadOptions) SetTailing(value bool) {
 // not a valid entry.  If iterator_extractor is not null, the Seek target
 // and iterator_upper_bound need to have the same prefix.
 // This is because ordering is not guaranteed outside of prefix domain.
-// There is no lower bound on the iterator. If needed, that can be easily
-// implemented.
 // Default: nullptr
 func (opts *ReadOptions) SetIterateUpperBound(key []byte) {
 	cKey := byteToChar(key)
 	cKeyLen := C.size_t(len(key))
 	C.rocksdb_readoptions_set_iterate_upper_bound(opts.c, cKey, cKeyLen)
 }
 
+// SetIterateLowerBound specifies "iterate_lower_bound", which defines
+// the smallest key at which the backward iterator can return an entry.
+// Once the bound is passed, Valid() will be false.
+// `iterate_lower_bound` is inclusive ie the bound value is a valid
+// entry.
+//
+// If prefix_extractor is not null, the Seek target and `iterate_lower_bound`
+// need to have the same prefix. This is because ordering is not guaranteed
+// outside of prefix domain.
+// Default: nullptr
+func (opts *ReadOptions) SetIterateLowerBound(key []byte) {
+	cKey := byteToChar(key)
+	cKeyLen := C.size_t(len(key))
+	C.rocksdb_readoptions_set_iterate_lower_bound(opts.c, cKey, cKeyLen)
+}
+
 // SetPinData specifies the value of "pin_data". If true, it keeps the blocks
 // loaded by the iterator pinned in memory as long as the iterator is not deleted,
 // If used when reading from tables created with