Fix slice transformers with no in_domain callback (#438)

src/slice_transform.rs

@@ -50,14 +50,7 @@ impl SliceTransform {
                 cb as *mut c_void,
                 Some(slice_transform_destructor_callback),
                 Some(transform_callback),
-                // this is ugly, but I can't get the compiler
-                // not to barf with "expected fn pointer, found fn item"
-                // without this. sorry.
-                if in_domain_fn.is_some() {
-                    Some(in_domain_callback)
-                } else {
-                    None
-                },
+                Some(in_domain_callback),
                 // this None points to the deprecated InRange callback
                 None,
                 Some(slice_transform_name_callback),
@@ -118,6 +111,9 @@ pub unsafe extern "C" fn in_domain_callback(
 ) -> u8 {
     let cb = &mut *(raw_cb as *mut TransformCallback);
     let key = slice::from_raw_parts(raw_key as *const u8, key_len as usize);
-    let in_domain = cb.in_domain_fn.unwrap();
+    if let Some(in_domain) = cb.in_domain_fn {
         in_domain(key) as u8
+    } else {
+        0xff
+    }
 }

tests/test_slice_transform.rs

@@ -64,3 +64,32 @@ pub fn test_slice_transform() {
         }
     }
 }
+
+#[test]
+fn test_no_in_domain() {
+    fn extract_suffix(slice: &[u8]) -> &[u8] {
+        if slice.len() > 4 {
+            &slice[slice.len() - 4..slice.len()]
+        } else {
+            slice
+        }
+    }
+
+    let db_path = DBPath::new("_rust_rocksdb_prefix_test");
+    {
+        let mut opts = Options::default();
+        opts.create_if_missing(true);
+        opts.set_prefix_extractor(SliceTransform::create(
+            "test slice transform",
+            extract_suffix,
+            None,
+        ));
+        opts.set_memtable_prefix_bloom_ratio(0.1);
+
+        let db = DB::open(&opts, &db_path).unwrap();
+        db.put(b"key_sfx1", b"a").unwrap();
+        db.put(b"key_sfx2", b"b").unwrap();
+
+        assert_eq!(db.get(b"key_sfx1").unwrap().unwrap(), b"a");
+    }
+}