wal: fix the unexpectedEOF error in the last wal.

It is safe to repair the unexpectedEOF error in the last wal. raft
will not send out message before the entry successfully comitted
into wal. Thus we can safely truncate the last entry in the wal
to repair.

etcdserver/storage.go

@@ -15,6 +15,7 @@
 package etcdserver
 
 import (
+	"io"
 	"log"
 	"os"
 	"path"
@@ -72,13 +73,28 @@ func (st *storage) SaveSnap(snap raftpb.Snapshot) error {
 }
 
 func readWAL(waldir string, snap walpb.Snapshot) (w *wal.WAL, id, cid types.ID, st raftpb.HardState, ents []raftpb.Entry) {
-	var err error
-	if w, err = wal.Open(waldir, snap); err != nil {
-		log.Fatalf("etcdserver: open wal error: %v", err)
-	}
-	var wmetadata []byte
-	if wmetadata, st, ents, err = w.ReadAll(); err != nil {
-		log.Fatalf("etcdserver: read wal error: %v", err)
+	var (
+		err       error
+		wmetadata []byte
+	)
+
+	for i := 0; i < 2; i++ {
+		if w, err = wal.Open(waldir, snap); err != nil {
+			log.Fatalf("etcdserver: open wal error: %v", err)
+		}
+		if wmetadata, st, ents, err = w.ReadAll(); err != nil {
+			w.Close()
+			if i != 0 || err != io.ErrUnexpectedEOF {
+				log.Fatalf("etcdserver: read wal error: %v", err)
+			}
+			if !wal.Repair(waldir) {
+				log.Fatalf("etcdserver: WAL error (%v) cannot be repaired", err)
+			} else {
+				log.Printf("etcdserver: repaired WAL error (%v)", err)
+			}
+			continue
+		}
+		break
 	}
 	var metadata pb.Metadata
 	pbutil.MustUnmarshal(&metadata, wmetadata)

wal/repair.go

@@ -0,0 +1,73 @@
+// Copyright 2015 CoreOS, Inc.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package wal
+
+import (
+	"io"
+	"os"
+	"path"
+
+	"github.com/coreos/etcd/pkg/fileutil"
+	"github.com/coreos/etcd/wal/walpb"
+)
+
+// Repair tries to repair the unexpectedEOF error in the
+// last wal file by truncating.
+func Repair(dirpath string) bool {
+	f, err := openLast(dirpath)
+	if err != nil {
+		return false
+	}
+
+	n := 0
+	rec := &walpb.Record{}
+
+	decoder := newDecoder(f)
+	defer decoder.close()
+	for {
+		err := decoder.decode(rec)
+		switch err {
+		case nil:
+			n += 8 + rec.Size()
+			continue
+		case io.EOF:
+			return true
+		case io.ErrUnexpectedEOF:
+			err = f.Truncate(int64(n))
+			if err != nil {
+				return false
+			}
+			err = f.Sync()
+			if err != nil {
+				return false
+			}
+			return true
+		}
+	}
+}
+
+// openLast opens the last wal file for read and write.
+func openLast(dirpath string) (*os.File, error) {
+	names, err := fileutil.ReadDir(dirpath)
+	if err != nil {
+		return nil, err
+	}
+	names = checkWalNames(names)
+	if len(names) == 0 {
+		return nil, ErrFileNotFound
+	}
+	last := path.Join(dirpath, names[len(names)-1])
+	return os.OpenFile(last, os.O_RDWR, 0)
+}

wal/repair_test.go

@@ -0,0 +1,91 @@
+// Copyright 2015 CoreOS, Inc.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package wal
+
+import (
+	"io"
+	"io/ioutil"
+	"os"
+	"testing"
+
+	"github.com/coreos/etcd/raft/raftpb"
+	"github.com/coreos/etcd/wal/walpb"
+)
+
+func TestRepair(t *testing.T) {
+	p, err := ioutil.TempDir(os.TempDir(), "waltest")
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer os.RemoveAll(p)
+	// create WAL
+	w, err := Create(p, nil)
+	defer w.Close()
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	n := 10
+	for i := 1; i <= n; i++ {
+		es := []raftpb.Entry{{Index: uint64(i)}}
+		if err = w.Save(raftpb.HardState{}, es); err != nil {
+			t.Fatal(err)
+		}
+	}
+	w.Close()
+
+	// break the wal.
+	f, err := openLast(p)
+	if err != nil {
+		t.Fatal(err)
+	}
+	offset, err := f.Seek(-4, os.SEEK_END)
+	if err != nil {
+		t.Fatal(err)
+	}
+	err = f.Truncate(offset)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	// verify we have broke the wal
+	w, err = Open(p, walpb.Snapshot{})
+	if err != nil {
+		t.Fatal(err)
+	}
+	_, _, _, err = w.ReadAll()
+	if err != io.ErrUnexpectedEOF {
+		t.Fatalf("err = %v, want %v", err, io.ErrUnexpectedEOF)
+	}
+	w.Close()
+
+	// repair the wal
+	ok := Repair(p)
+	if !ok {
+		t.Fatalf("fix = %t, want %t", ok, true)
+	}
+
+	w, err = Open(p, walpb.Snapshot{})
+	if err != nil {
+		t.Fatal(err)
+	}
+	_, _, ents, err := w.ReadAll()
+	if err != nil {
+		t.Fatalf("err = %v, want %v", err, nil)
+	}
+	if len(ents) != n-1 {
+		t.Fatalf("len(ents) = %d, want %d", len(ents), n-1)
+	}
+}

wal/wal.go

@@ -414,14 +414,14 @@ func (w *WAL) Save(st raftpb.HardState, ents []raftpb.Entry) error {
 	}
 
 	// TODO(xiangli): no more reference operator
-	if err := w.saveState(&st); err != nil {
-		return err
-	}
 	for i := range ents {
 		if err := w.saveEntry(&ents[i]); err != nil {
 			return err
 		}
 	}
+	if err := w.saveState(&st); err != nil {
+		return err
+	}
 
 	fstat, err := w.f.Stat()
 	if err != nil {