lmdb: Return dedicated ErrNotFound from Txn.Get and Cursor.Get

lmdb/bench_test.go

@@ -271,6 +271,33 @@ func BenchmarkTxn_Get_raw_ro(b *testing.B) {
 	}
 }
 
+// Get a missing key, with RawRead turned on.
+func BenchmarkTxn_Get_missing_raw(b *testing.B) {
+	env := setup(b)
+	defer clean(env, b)
+
+	dbi := openBenchDBI(b, env)
+
+	err := env.View(func(txn *Txn) (err error) {
+		txn.RawRead = true
+		key := []byte("does not exist")
+
+		b.ResetTimer()
+		defer b.StopTimer()
+		for i := 0; i < b.N; i++ {
+			_, err := txn.Get(dbi, key)
+			if !IsNotFound(err) {
+				b.Fatalf("found non-existent key: %v", err)
+			}
+		}
+		return nil
+	})
+	if err != nil {
+		b.Error(err)
+		return
+	}
+}
+
 // repeatedly scan all the values in a database.
 func BenchmarkScan_ro(b *testing.B) {
 	initRandSource(b)

lmdb/cursor.go

@@ -137,16 +137,27 @@ func (c *Cursor) DBI() DBI {
 //
 // Get ignores setval if setkey is empty.
 //
+// Returns ErrNotFound if setkey is not present.
+//
 // See mdb_cursor_get.
 func (c *Cursor) Get(setkey, setval []byte, op uint) (key, val []byte, err error) {
+	var ret C.int
 	switch {
 	case len(setkey) == 0:
-		err = c.getVal0(op)
+		ret = c.getVal0(op)
 	case len(setval) == 0:
-		err = c.getVal1(setkey, op)
+		ret = c.getVal1(setkey, op)
 	default:
-		err = c.getVal2(setkey, setval, op)
+		ret = c.getVal2(setkey, setval, op)
+	}
+
+	if ret == C.MDB_NOTFOUND {
+		*c.txn.key = C.MDB_val{}
+		*c.txn.val = C.MDB_val{}
+		return nil, nil, ErrNotFound
 	}
+
+	err = operrno("mdb_cursor_get", ret)
 	if err != nil {
 		*c.txn.key = C.MDB_val{}
 		*c.txn.val = C.MDB_val{}
@@ -163,38 +174,35 @@ func (c *Cursor) Get(setkey, setval []byte, op uint) (key, val []byte, err error
 // data for reference (Next, First, Last, etc).
 //
 // See mdb_cursor_get.
-func (c *Cursor) getVal0(op uint) error {
-	ret := C.mdb_cursor_get(c._c, c.txn.key, c.txn.val, C.MDB_cursor_op(op))
-	return operrno("mdb_cursor_get", ret)
+func (c *Cursor) getVal0(op uint) C.int {
+	return C.mdb_cursor_get(c._c, c.txn.key, c.txn.val, C.MDB_cursor_op(op))
 }
 
 // getVal1 retrieves items from the database using key data for reference
 // (Set, SetRange, etc).
 //
 // See mdb_cursor_get.
-func (c *Cursor) getVal1(setkey []byte, op uint) error {
-	ret := C.lmdbgo_mdb_cursor_get1(
+func (c *Cursor) getVal1(setkey []byte, op uint) C.int {
+	return C.lmdbgo_mdb_cursor_get1(
 		c._c,
 		unsafe.Pointer(&setkey[0]), C.size_t(len(setkey)),
 		c.txn.key, c.txn.val,
 		C.MDB_cursor_op(op),
 	)
-	return operrno("mdb_cursor_get", ret)
 }
 
 // getVal2 retrieves items from the database using key and value data for
 // reference (GetBoth, GetBothRange, etc).
 //
 // See mdb_cursor_get.
-func (c *Cursor) getVal2(setkey, setval []byte, op uint) error {
-	ret := C.lmdbgo_mdb_cursor_get2(
+func (c *Cursor) getVal2(setkey, setval []byte, op uint) C.int {
+	return C.lmdbgo_mdb_cursor_get2(
 		c._c,
 		unsafe.Pointer(&setkey[0]), C.size_t(len(setkey)),
 		unsafe.Pointer(&setval[0]), C.size_t(len(setval)),
 		c.txn.key, c.txn.val,
 		C.MDB_cursor_op(op),
 	)
-	return operrno("mdb_cursor_get", ret)
 }
 
 func (c *Cursor) putNilKey(flags uint) error {

lmdb/cursor_test.go

@@ -811,3 +811,45 @@ func BenchmarkCursor_Renew(b *testing.B) {
 		return nil
 	})
 }
+
+func BenchmarkCursor_Get_missing_raw(b *testing.B) {
+	env := setup(b)
+	defer clean(env, b)
+
+	var db DBI
+	err := env.View(func(txn *Txn) (err error) {
+		db, err = txn.OpenRoot(0)
+		if err != nil {
+			return err
+		}
+		return nil
+	})
+	if err != nil {
+		b.Error(err)
+		return
+	}
+
+	err = env.View(func(txn *Txn) (err error) {
+		cur, err := txn.OpenCursor(db)
+		if err != nil {
+			return err
+		}
+		defer cur.Close()
+
+		key := []byte("does not exist")
+
+		b.ResetTimer()
+		defer b.StopTimer()
+
+		for i := 0; i < b.N; i++ {
+			if _, _, err := cur.Get(key, nil, SetKey); !IsNotFound(err) {
+				b.Fatal("found key that should not exist")
+			}
+		}
+		return
+	})
+	if err != nil {
+		b.Error(err)
+		return
+	}
+}

lmdb/error.go

@@ -70,6 +70,9 @@ const (
 //		lmdb.IsErrnoFn(err, os.IsPermission)
 type Errno C.int
 
+// ErrNotFound is returned by Txn.Get and Cursor.Get
+var ErrNotFound = &OpError{"lmdb", NotFound}
+
 // minimum and maximum values produced for the Errno type. syscall.Errnos of
 // other values may still be produced.
 const minErrno, maxErrno C.int = C.MDB_KEYEXIST, C.MDB_LAST_ERRCODE
@@ -87,7 +90,7 @@ func _operrno(op string, ret int) error {
 // not exist or if the Cursor reached the end of the database without locating
 // a value (EOF).
 func IsNotFound(err error) bool {
-	return IsErrno(err, NotFound)
+	return err == ErrNotFound
 }
 
 // IsNotExist returns true the path passed to the Env.Open method does not
@@ -124,6 +127,9 @@ func IsErrnoFn(err error, fn func(error) bool) bool {
 	if err == nil {
 		return false
 	}
+	if err == ErrNotFound {
+		return fn(NotFound)
+	}
 	if err, ok := err.(*OpError); ok {
 		return fn(err.Errno)
 	}

lmdb/txn.go

@@ -279,6 +279,8 @@ func (txn *Txn) bytes(val *C.MDB_val) []byte {
 // returned by Get references a readonly section of memory that must not be
 // accessed after txn has terminated.
 //
+// Returns ErrNotFound if the key is not present in dbi.
+//
 // See mdb_get.
 func (txn *Txn) Get(dbi DBI, key []byte) ([]byte, error) {
 	kdata, kn := valBytes(key)
@@ -287,6 +289,12 @@ func (txn *Txn) Get(dbi DBI, key []byte) ([]byte, error) {
 		unsafe.Pointer(&kdata[0]), C.size_t(kn),
 		txn.val,
 	)
+
+	if ret == C.MDB_NOTFOUND {
+		*txn.val = C.MDB_val{}
+		return nil, ErrNotFound
+	}
+
 	err := operrno("mdb_get", ret)
 	if err != nil {
 		*txn.val = C.MDB_val{}
@@ -352,6 +360,8 @@ func (txn *Txn) PutReserve(dbi DBI, key []byte, n int, flags uint) ([]byte, erro
 // Del deletes an item from database dbi.  Del ignores val unless dbi has the
 // DupSort flag.
 //
+// Returns ErrNotFound if the key is not present in dbi.
+//
 // See mdb_del.
 func (txn *Txn) Del(dbi DBI, key, val []byte) error {
 	kdata, kn := valBytes(key)
@@ -361,6 +371,11 @@ func (txn *Txn) Del(dbi DBI, key, val []byte) error {
 		unsafe.Pointer(&kdata[0]), C.size_t(kn),
 		unsafe.Pointer(&vdata[0]), C.size_t(vn),
 	)
+
+	if ret == C.MDB_NOTFOUND {
+		return ErrNotFound
+	}
+
 	return operrno("mdb_del", ret)
 }