wal: make new work

wal/wal.go

@@ -22,7 +22,13 @@ type WAL struct {
 }
 
 func New(path string) (*WAL, error) {
-	f, err := os.Create(path)
+	f, err := os.Open(path)
+	if err == nil {
+		f.Close()
+		return nil, os.ErrExist
+	}
+
+	f, err = os.Create(path)
 	if err != nil {
 		return nil, err
 	}
@@ -30,6 +36,13 @@ func New(path string) (*WAL, error) {
 	return &WAL{f, bw}, nil
 }
 
+func (w *WAL) Close() {
+	if w.f != nil {
+		w.flush()
+		w.f.Close()
+	}
+}
+
 func (w *WAL) writeInfo(id int64) error {
 	// | 8 bytes | 8 bytes |  8 bytes |
 	// | type    |   len   |   nodeid |

wal/wal_test.go

@@ -0,0 +1,32 @@
+package wal
+
+import (
+	"io/ioutil"
+	"os"
+	"testing"
+)
+
+func TestNew(t *testing.T) {
+	f, err := ioutil.TempFile(os.TempDir(), "waltest")
+	if err != nil {
+		t.Fatal(err)
+	}
+	p := f.Name()
+	_, err = New(p)
+	if err == nil || err != os.ErrExist {
+		t.Errorf("err = %v, want %v", err, os.ErrExist)
+	}
+	err = os.Remove(p)
+	if err != nil {
+		t.Fatal(err)
+	}
+	w, err := New(p)
+	if err != nil {
+		t.Errorf("err = %v, want nil", err)
+	}
+	w.Close()
+	err = os.Remove(p)
+	if err != nil {
+		t.Fatal(err)
+	}
+}