wal: wal.OpenFromIndex -> wal.OpenAtIndex

The first entry read from the wal should be the index provided. This
name makes that more clear.

main.go

@@ -107,7 +107,7 @@ func startRaft(id int64, peerIDs []int64, waldir string) (raft.Node, *wal.WAL) {
 
 	// restart a node from previous wal
 	// TODO(xiangli): check snapshot; not open from zero
-	w, err := wal.OpenFromIndex(waldir, 0)
+	w, err := wal.OpenAtIndex(waldir, 0)
 	if err != nil {
 		log.Fatal(err)
 	}

wal/doc.go

@@ -44,7 +44,7 @@ Cut is issues 0x10 entries later then the file will be called:
 
 At a later time a WAL can be opened at a particular raft index:
 
-	w, err := wal.OpenFromIndex("/var/lib/etcd", 0)
+	w, err := wal.OpenAtIndex("/var/lib/etcd", 0)
 	...
 
 Additional items cannot be Saved to this WAL until all of the items from 0 to

wal/wal.go

@@ -92,11 +92,11 @@ func Create(dirpath string) (*WAL, error) {
 	return w, nil
 }
 
-// OpenFromIndex opens the WAL files containing all the entries after
-// the given index.
-// The returned WAL is ready to read. The WAL cannot be appended to before
-// reading out all of its previous records.
-func OpenFromIndex(dirpath string, index int64) (*WAL, error) {
+// OpenAtIndex opens the WAL at the given index.
+// The returned WAL is ready to read and the first record will be the given
+// index. The WAL cannot be appended to before reading out all of its
+// previous records.
+func OpenAtIndex(dirpath string, index int64) (*WAL, error) {
 	log.Printf("path=%s wal.load index=%d", dirpath, index)
 	names, err := readDir(dirpath)
 	if err != nil {

wal/wal_test.go

@@ -65,7 +65,7 @@ func TestNewForInitedDir(t *testing.T) {
 	}
 }
 
-func TestOpenFromIndex(t *testing.T) {
+func TestOpenAtIndex(t *testing.T) {
 	dir, err := ioutil.TempDir(os.TempDir(), "waltest")
 	if err != nil {
 		t.Fatal(err)
@@ -78,7 +78,7 @@ func TestOpenFromIndex(t *testing.T) {
 	}
 	f.Close()
 
-	w, err := OpenFromIndex(dir, 0)
+	w, err := OpenAtIndex(dir, 0)
 	if err != nil {
 		t.Fatalf("err = %v, want nil", err)
 	}
@@ -94,7 +94,7 @@ func TestOpenFromIndex(t *testing.T) {
 	}
 	f.Close()
 
-	w, err = OpenFromIndex(dir, 5)
+	w, err = OpenAtIndex(dir, 5)
 	if err != nil {
 		t.Fatalf("err = %v, want nil", err)
 	}
@@ -108,7 +108,7 @@ func TestOpenFromIndex(t *testing.T) {
 		t.Fatal(err)
 	}
 	defer os.RemoveAll(emptydir)
-	if _, err = OpenFromIndex(emptydir, 0); err != ErrNotFound {
+	if _, err = OpenAtIndex(emptydir, 0); err != ErrNotFound {
 		t.Errorf("err = %v, want %v", err, ErrNotFound)
 	}
 }
@@ -176,7 +176,7 @@ func TestRecover(t *testing.T) {
 	}
 	w.Close()
 
-	if w, err = OpenFromIndex(p, 0); err != nil {
+	if w, err = OpenAtIndex(p, 0); err != nil {
 		t.Fatal(err)
 	}
 	id, state, entries, err := w.ReadAll()
@@ -301,7 +301,7 @@ func TestRecoverAfterCut(t *testing.T) {
 	}
 
 	for i := 0; i < 10; i++ {
-		w, err := OpenFromIndex(p, int64(i))
+		w, err := OpenAtIndex(p, int64(i))
 		if i <= 3 {
 			if err != ErrNotFound {
 				t.Errorf("#%d: err = %v, want %v", i, err, ErrNotFound)