support lower bound for ReadOptions (#168)

librocksdb_sys/crocksdb/c.cc

@@ -127,6 +127,7 @@ struct crocksdb_fifo_compaction_options_t { CompactionOptionsFIFO rep; };
 struct crocksdb_readoptions_t {
    ReadOptions rep;
    Slice upper_bound; // stack variable to set pointer to in ReadOptions
+   Slice lower_bound;
 };
 struct crocksdb_writeoptions_t    { WriteOptions      rep; };
 struct crocksdb_options_t         { Options           rep; };
@@ -2683,13 +2684,24 @@ void crocksdb_readoptions_set_snapshot(
   opt->rep.snapshot = (snap ? snap->rep : nullptr);
 }
 
+void crocksdb_readoptions_set_iterate_lower_bound(
+  crocksdb_readoptions_t* opt,
+  const char* key, size_t keylen) {
+  if (key == nullptr) {
+    opt->lower_bound = Slice();
+    opt->rep.iterate_lower_bound = nullptr;
+  } else {
+    opt->lower_bound = Slice(key, keylen);
+    opt->rep.iterate_lower_bound = &opt->lower_bound;
+  }
+}
+
 void crocksdb_readoptions_set_iterate_upper_bound(
     crocksdb_readoptions_t* opt,
     const char* key, size_t keylen) {
   if (key == nullptr) {
     opt->upper_bound = Slice();
     opt->rep.iterate_upper_bound = nullptr;
-
   } else {
     opt->upper_bound = Slice(key, keylen);
     opt->rep.iterate_upper_bound = &opt->upper_bound;

librocksdb_sys/crocksdb/crocksdb/c.h

@@ -1107,6 +1107,8 @@ extern C_ROCKSDB_LIBRARY_API void crocksdb_readoptions_set_fill_cache(
     crocksdb_readoptions_t*, unsigned char);
 extern C_ROCKSDB_LIBRARY_API void crocksdb_readoptions_set_snapshot(
     crocksdb_readoptions_t*, const crocksdb_snapshot_t*);
+extern C_ROCKSDB_LIBRARY_API void crocksdb_readoptions_set_iterate_lower_bound(
+    crocksdb_readoptions_t*, const char* key, size_t keylen);
 extern C_ROCKSDB_LIBRARY_API void crocksdb_readoptions_set_iterate_upper_bound(
     crocksdb_readoptions_t*, const char* key, size_t keylen);
 extern C_ROCKSDB_LIBRARY_API void crocksdb_readoptions_set_read_tier(

librocksdb_sys/src/lib.rs

@@ -596,6 +596,11 @@ extern "C" {
         readopts: *mut DBReadOptions,
         snapshot: *const DBSnapshot,
     );
+    pub fn crocksdb_readoptions_set_iterate_lower_bound(
+        readopts: *mut DBReadOptions,
+        k: *const u8,
+        kLen: size_t,
+    );
     pub fn crocksdb_readoptions_set_iterate_upper_bound(
         readopts: *mut DBReadOptions,
         k: *const u8,

src/rocksdb_options.rs

@@ -231,6 +231,7 @@ impl UnsafeSnap {
 
 pub struct ReadOptions {
     inner: *mut DBReadOptions,
+    lower_bound: Vec<u8>,
     upper_bound: Vec<u8>,
 }
 
@@ -247,6 +248,7 @@ impl Default for ReadOptions {
             assert!(!opts.is_null(), "Unable to create rocksdb read options");
             ReadOptions {
                 inner: opts,
+                lower_bound: vec![],
                 upper_bound: vec![],
             }
         }
@@ -279,6 +281,17 @@ impl ReadOptions {
         crocksdb_ffi::crocksdb_readoptions_set_snapshot(self.inner, snapshot.inner);
     }
 
+    pub fn set_iterate_lower_bound(&mut self, key: &[u8]) {
+        self.lower_bound = Vec::from(key);
+        unsafe {
+            crocksdb_ffi::crocksdb_readoptions_set_iterate_lower_bound(
+                self.inner,
+                self.lower_bound.as_ptr(),
+                self.lower_bound.len(),
+            );
+        }
+    }
+
     pub fn set_iterate_upper_bound(&mut self, key: &[u8]) {
         self.upper_bound = Vec::from(key);
         unsafe {

tests/test_rocksdb_options.rs

@@ -584,6 +584,28 @@ fn test_read_options() {
     assert!(key_count == 3);
 }
 
+#[test]
+fn test_readoptions_lower_bound() {
+    let path = TempDir::new("_rust_rocksdb_readoptions_lower_bound").expect("");
+    let db = DB::open_default(path.path().to_str().unwrap()).unwrap();
+
+    db.put(b"k1", b"b").unwrap();
+    db.put(b"k2", b"a").unwrap();
+    db.put(b"k3", b"a").unwrap();
+
+    let mut read_opts = ReadOptions::new();
+    let lower_bound = b"k2";
+    read_opts.set_iterate_lower_bound(lower_bound.as_ref());
+    let mut iter = db.iter_opt(read_opts);
+    iter.seek(SeekKey::Key(b"k3"));
+    let mut count = 0;
+    while iter.valid() {
+        count += 1;
+        iter.prev();
+    }
+    assert_eq!(count, 2);
+}
+
 #[test]
 fn test_block_based_options() {
     let path = TempDir::new("_rust_rocksdb_block_based_options").expect("");