kv and deps: update to fix read problem on windows

github.com/cznic/kv rev: c966980e3e8456175d4407fcbb0287057d9d0862

http://camlistore.org/issue/214

Change-Id: I15d658710059c823b775db6cc6fa14c1a32b98fb

third_party/github.com/cznic/exp/dbm/all_test.go

@@ -24,6 +24,7 @@ import (
 	"time"
 
 	"camlistore.org/third_party/github.com/cznic/exp/lldb"
+	"camlistore.org/third_party/github.com/cznic/fileutil"
 )
 
 var (
@@ -795,7 +796,7 @@ func TestSlice0(t *testing.T) {
 			ga = append(ga, strings.Join(a, ","))
 			return true, nil
 		}); err != nil {
-			if err != io.EOF {
+			if !fileutil.IsEOF(err) {
 				t.Fatal(i, err)
 			}
 		}
@@ -2116,7 +2117,7 @@ func TestFileReadAtWriteAt(t *testing.T) {
 			from, to = 0, n2
 		}
 		n, err := f.ReadAt(b[from:to], int64(from))
-		if err != nil && (err != io.EOF && n != 0) {
+		if err != nil && (!fileutil.IsEOF(err) && n != 0) {
 			t.Error(fsz(), from, to, err)
 			return
 		}

third_party/github.com/cznic/exp/dbm/etc.go

@@ -7,10 +7,10 @@ package dbm
 import (
 	"bytes"
 	"fmt"
-	"io"
 
 	"camlistore.org/third_party/github.com/cznic/exp/lldb"
 	"camlistore.org/third_party/github.com/cznic/mathutil"
+	"camlistore.org/third_party/github.com/cznic/fileutil"
 )
 
 type header struct {
@@ -149,7 +149,7 @@ func encVal(val interface{}) (r []byte, err error) {
 }
 
 func noEof(e error) (err error) {
-	if e != io.EOF {
+	if !fileutil.IsEOF(e) {
 		err = e
 	}
 	return

third_party/github.com/cznic/exp/dbm/file.go

@@ -11,6 +11,7 @@ import (
 
 	"camlistore.org/third_party/github.com/cznic/exp/lldb"
 	"camlistore.org/third_party/github.com/cznic/mathutil"
+	"camlistore.org/third_party/github.com/cznic/fileutil"
 )
 
 /*
@@ -375,7 +376,7 @@ func (f *File) ReadFrom(r io.Reader) (n int64, err error) {
 			n += int64(rn)
 		}
 	}
-	if rerr != io.EOF {
+	if !fileutil.IsEOF(rerr) {
 		err = rerr
 	}
 	return
@@ -439,7 +440,7 @@ func (f *File) WriteTo(w io.Writer) (n int64, err error) {
 			n += int64(wn)
 		}
 	}
-	if rerr != io.EOF {
+	if !fileutil.IsEOF(rerr) {
 		err = rerr
 	}
 	return

third_party/github.com/cznic/exp/lldb/2pc.go

@@ -13,6 +13,7 @@ import (
 	"io"
 	"os"
 
+	"camlistore.org/third_party/github.com/cznic/fileutil"
 	"camlistore.org/third_party/github.com/cznic/mathutil"
 )
 
@@ -161,7 +162,7 @@ func NewACIDFiler(db Filer, wal *os.File) (r *ACIDFiler0, err error) {
 			for {
 				k, v, err := enum.current()
 				if err != nil {
-					if err == io.EOF {
+					if fileutil.IsEOF(err) {
 						break
 					}
 
@@ -173,7 +174,7 @@ func NewACIDFiler(db Filer, wal *os.File) (r *ACIDFiler0, err error) {
 				}
 
 				if err = enum.next(); err != nil {
-					if err == io.EOF {
+					if fileutil.IsEOF(err) {
 						break
 					}
 
@@ -299,7 +300,7 @@ func (a *ACIDFiler0) recoverDb(db Filer) (err error) {
 			for {
 				k, v, err := enum.current()
 				if err != nil {
-					if err == io.EOF {
+					if fileutil.IsEOF(err) {
 						break
 					}
 
@@ -311,7 +312,7 @@ func (a *ACIDFiler0) recoverDb(db Filer) (err error) {
 				}
 
 				if err = enum.next(); err != nil {
-					if err == io.EOF {
+					if fileutil.IsEOF(err) {
 						break
 					}
 

third_party/github.com/cznic/exp/lldb/btree.go

@@ -13,6 +13,7 @@ import (
 	"strings"
 
 	"camlistore.org/third_party/github.com/cznic/bufs"
+	"camlistore.org/third_party/github.com/cznic/fileutil"
 	"camlistore.org/third_party/github.com/cznic/sortutil"
 )
 
@@ -184,7 +185,7 @@ func (t *BTree) Dump(w io.Writer) (err error) {
 
 		err = enum.next()
 		if err != nil {
-			if err == io.EOF {
+			if fileutil.IsEOF(err) {
 				err = nil
 				break
 			}

third_party/github.com/cznic/exp/lldb/btree_test.go

@@ -10,13 +10,13 @@ import (
 	"encoding/hex"
 	"flag"
 	"fmt"
-	"io"
 	"math"
 	"math/rand"
 	"os"
 	"runtime"
 	"testing"
 
+	"camlistore.org/third_party/github.com/cznic/fileutil"
 	"camlistore.org/third_party/github.com/cznic/mathutil"
 )
 
@@ -632,15 +632,15 @@ func TestbTreeNext(t *testing.T) {
 		t.Fatal(err)
 	}
 
-	if _, _, err = enum.current(); err != io.EOF {
+	if _, _, err = enum.current(); !fileutil.IsEOF(err) {
 		t.Fatal(err)
 	}
 
-	if err = enum.next(); err != io.EOF {
+	if err = enum.next(); !fileutil.IsEOF(err) {
 		t.Fatal(err)
 	}
 
-	if err = enum.prev(); err != io.EOF {
+	if err = enum.prev(); !fileutil.IsEOF(err) {
 		t.Fatal(err)
 	}
 
@@ -683,7 +683,7 @@ func TestbTreeNext(t *testing.T) {
 		t.Fatal(err)
 	}
 
-	if err = enum.next(); N > 1 && err != io.EOF {
+	if err = enum.next(); N > 1 && !fileutil.IsEOF(err) {
 		t.Fatal(err)
 	}
 
@@ -697,11 +697,11 @@ func TestbTreeNext(t *testing.T) {
 	}
 
 	// index: N
-	if _, _, err = enum.current(); err != io.EOF {
+	if _, _, err = enum.current(); !fileutil.IsEOF(err) {
 		t.Fatal(err)
 	}
 
-	if err = enum.next(); N > 1 && err != io.EOF {
+	if err = enum.next(); N > 1 && !fileutil.IsEOF(err) {
 		t.Fatal(err)
 	}
 
@@ -727,7 +727,7 @@ func TestbTreeNext(t *testing.T) {
 
 		switch {
 		case i == N:
-			if err := enum.next(); err != io.EOF {
+			if err := enum.next(); !fileutil.IsEOF(err) {
 				t.Fatal(err)
 			}
 		default:
@@ -747,15 +747,15 @@ func TestbTreePrev(t *testing.T) {
 		t.Fatal(err)
 	}
 
-	if _, _, err = enum.current(); err != io.EOF {
+	if _, _, err = enum.current(); !fileutil.IsEOF(err) {
 		t.Fatal(err)
 	}
 
-	if err = enum.next(); err != io.EOF {
+	if err = enum.next(); !fileutil.IsEOF(err) {
 		t.Fatal(err)
 	}
 
-	if err = enum.prev(); err != io.EOF {
+	if err = enum.prev(); !fileutil.IsEOF(err) {
 		t.Fatal(err)
 	}
 
@@ -780,7 +780,7 @@ func TestbTreePrev(t *testing.T) {
 		t.Fatal(err)
 	}
 
-	if err = enum.prev(); err != io.EOF {
+	if err = enum.prev(); !fileutil.IsEOF(err) {
 		t.Fatal(err)
 	}
 
@@ -812,7 +812,7 @@ func TestbTreePrev(t *testing.T) {
 	}
 
 	// index: N
-	if _, _, err = enum.current(); err != io.EOF {
+	if _, _, err = enum.current(); !fileutil.IsEOF(err) {
 		t.Fatal(err)
 	}
 
@@ -842,7 +842,7 @@ func TestbTreePrev(t *testing.T) {
 
 		switch {
 		case i == 1:
-			if err := enum.prev(); err != io.EOF {
+			if err := enum.prev(); !fileutil.IsEOF(err) {
 				t.Fatal(err)
 			}
 		default:
@@ -1095,7 +1095,7 @@ func TestseekFirst(t *testing.T) {
 	bt := NewBTree(nil)
 
 	enum, err := bt.seekFirst()
-	if err != io.EOF {
+	if !fileutil.IsEOF(err) {
 		t.Fatal(err)
 	}
 
@@ -1106,12 +1106,12 @@ func TestseekFirst(t *testing.T) {
 	}
 
 	err = enum.prev()
-	if err != io.EOF {
+	if !fileutil.IsEOF(err) {
 		t.Fatal(err)
 	}
 
 	err = enum.next()
-	if err != io.EOF {
+	if !fileutil.IsEOF(err) {
 		t.Fatal(err)
 	}
 
@@ -1131,7 +1131,7 @@ func TestseekFirst(t *testing.T) {
 	}
 
 	err = enum.prev()
-	if err != io.EOF {
+	if !fileutil.IsEOF(err) {
 		t.Fatal(err)
 	}
 
@@ -1163,7 +1163,7 @@ func TestseekLast(t *testing.T) {
 	bt := NewBTree(nil)
 
 	enum, err := bt.seekFirst()
-	if err != io.EOF {
+	if !fileutil.IsEOF(err) {
 		t.Fatal(err)
 	}
 
@@ -1174,12 +1174,12 @@ func TestseekLast(t *testing.T) {
 	}
 
 	err = enum.prev()
-	if err != io.EOF {
+	if !fileutil.IsEOF(err) {
 		t.Fatal(err)
 	}
 
 	err = enum.next()
-	if err != io.EOF {
+	if !fileutil.IsEOF(err) {
 		t.Fatal(err)
 	}
 
@@ -1199,7 +1199,7 @@ func TestseekLast(t *testing.T) {
 	}
 
 	err = enum.next()
-	if err != io.EOF {
+	if !fileutil.IsEOF(err) {
 		t.Fatal(err)
 	}
 
@@ -1597,7 +1597,7 @@ func TestBTreeSeekNext(t *testing.T) {
 
 				k, v, err := en.Next()
 				if err != nil {
-					if err != io.EOF {
+					if !fileutil.IsEOF(err) {
 						t.Fatal(i, err)
 					}
 
@@ -1687,7 +1687,7 @@ func TestBTreeSeekPrev(t *testing.T) {
 
 				k, v, err := en.Prev()
 				if err != nil {
-					if err != io.EOF {
+					if !fileutil.IsEOF(err) {
 						t.Fatal(i, err)
 					}
 

third_party/github.com/cznic/exp/lldb/filer_test.go

@@ -7,12 +7,13 @@ package lldb
 import (
 	"bytes"
 	"encoding/hex"
-	"io"
 	"io/ioutil"
 	"math/rand"
 	"os"
 	"runtime"
 	"testing"
+
+	"camlistore.org/third_party/github.com/cznic/fileutil"
 )
 
 // Bench knobs.
@@ -284,7 +285,7 @@ func testFilerReadAtWriteAt(t *testing.T, nf newFunc) {
 			from, to = 0, n2
 		}
 		n, err := f.ReadAt(b[from:to], int64(from))
-		if err != nil && (err != io.EOF && n != 0) {
+		if err != nil && (!fileutil.IsEOF(err) && n != 0) {
 			fsz, err = f.Size()
 			if err != nil {
 				t.Error(err)

third_party/github.com/cznic/exp/lldb/memfiler.go

@@ -79,8 +79,10 @@ package lldb
 import (
 	"bytes"
 	"fmt"
-	"camlistore.org/third_party/github.com/cznic/mathutil"
 	"io"
+
+	"camlistore.org/third_party/github.com/cznic/fileutil"
+	"camlistore.org/third_party/github.com/cznic/mathutil"
 )
 
 const (
@@ -213,7 +215,7 @@ func (f *MemFiler) ReadFrom(r io.Reader) (n int64, err error) {
 			n += int64(rn)
 		}
 	}
-	if rerr != io.EOF {
+	if !fileutil.IsEOF(rerr) {
 		err = rerr
 	}
 	return
@@ -335,7 +337,7 @@ func (f *MemFiler) WriteTo(w io.Writer) (n int64, err error) {
 			n += int64(wn)
 		}
 	}
-	if rerr != io.EOF {
+	if !fileutil.IsEOF(rerr) {
 		err = rerr
 	}
 	return

third_party/github.com/cznic/exp/lldb/xact.go

@@ -54,6 +54,7 @@ import (
 	"fmt"
 	"io"
 
+	"camlistore.org/third_party/github.com/cznic/fileutil"
 	"camlistore.org/third_party/github.com/cznic/mathutil"
 )
 
@@ -151,7 +152,7 @@ func (f *bitFiler) ReadAt(b []byte, off int64) (n int, err error) {
 			pg = &bitPage{}
 			if f.parent != nil {
 				_, err = f.parent.ReadAt(pg.data[:], off&^bfMask)
-				if err != nil && err != io.EOF {
+				if err != nil && !fileutil.IsEOF(err) {
 					return
 				}
 
@@ -209,7 +210,7 @@ func (f *bitFiler) WriteAt(b []byte, off int64) (n int, err error) {
 			pg = &bitPage{}
 			if f.parent != nil {
 				_, err = f.parent.ReadAt(pg.data[:], off&^bfMask)
-				if err != nil && err != io.EOF {
+				if err != nil && !fileutil.IsEOF(err) {
 					return
 				}
 

third_party/github.com/cznic/exp/lldb/xact_test.go

@@ -12,6 +12,7 @@ import (
 	"math/rand"
 	"testing"
 
+	"camlistore.org/third_party/github.com/cznic/fileutil"
 	"camlistore.org/third_party/github.com/cznic/mathutil"
 )
 
@@ -182,12 +183,12 @@ func TestRollbackFiler3(t *testing.T) {
 	}
 
 	n, err := r.ReadAt([]byte{0}, 0)
-	if n != 0 || err != io.EOF {
+	if n != 0 || !fileutil.IsEOF(err) {
 		t.Fatal(n, err)
 	}
 
 	n, err = r.ReadAt([]byte{0}, 1e6)
-	if n != 0 || err != io.EOF {
+	if n != 0 || !fileutil.IsEOF(err) {
 		t.Fatal(n, err)
 	}
 

third_party/github.com/cznic/fileutil/fileutil_arm.go

@@ -7,6 +7,7 @@
 package fileutil
 
 import (
+	"io"
 	"os"
 )
 
@@ -21,3 +22,6 @@ func PunchHole(f *os.File, off, len int64) error {
 func Fadvise(f *os.File, off, len int64, advice FadviseAdvice) error {
 	return nil
 }
+
+// IsEOF reports whether err is an EOF condition.
+func IsEOF(err error) bool { return err == io.EOF }

third_party/github.com/cznic/fileutil/fileutil_darwin.go

@@ -7,6 +7,7 @@
 package fileutil
 
 import (
+	"io"
 	"os"
 )
 
@@ -21,3 +22,6 @@ func PunchHole(f *os.File, off, len int64) error {
 func Fadvise(f *os.File, off, len int64, advice FadviseAdvice) error {
 	return nil
 }
+
+// IsEOF reports whether err is an EOF condition.
+func IsEOF(err error) bool { return err == io.EOF }

third_party/github.com/cznic/fileutil/fileutil_freebsd.go

@@ -1,23 +1,27 @@
-// Copyright (c) 2011 CZ.NIC z.s.p.o. All rights reserved.
+// Copyright (c) 2013 wathiede[0]. All rights reserved.
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
-
-// blame: jnml, labs.nic.cz
+//
+//	[0]: https://github.com/wathiede
 
 package fileutil
 
 import (
+	"io"
 	"os"
 )
 
 // PunchHole deallocates space inside a file in the byte range starting at
-// offset and continuing for len bytes. Unimplemented on FreeBSD
+// offset and continuing for len bytes. Unimplemented on FreeBSD.
 func PunchHole(f *os.File, off, len int64) error {
 	return nil
 }
 
 // Fadvise predeclares an access pattern for file data.  See also 'man 2
-// posix_fadvise'. Unimplemented on FreeBSD
+// posix_fadvise'. Unimplemented on FreeBSD.
 func Fadvise(f *os.File, off, len int64, advice FadviseAdvice) error {
 	return nil
 }
+
+// IsEOF reports whether err is an EOF condition.
+func IsEOF(err error) bool { return err == io.EOF }

third_party/github.com/cznic/fileutil/fileutil_linux.go

@@ -8,6 +8,7 @@ package fileutil
 
 import (
 	"bytes"
+	"io"
 	"io/ioutil"
 	"os"
 	"strconv"
@@ -32,6 +33,9 @@ func init() {
 	}
 
 	tokens := bytes.Split(b, []byte("."))
+	if len(tokens) > 3 {
+		tokens = tokens[:3]
+	}
 	switch len(tokens) {
 	case 3:
 		// Supported since kernel 2.6.38
@@ -43,7 +47,7 @@ func init() {
 			puncher = func(*os.File, int64, int64) error { return nil }
 		}
 	default:
-		panic(n)
+		puncher = func(*os.File, int64, int64) error { return nil }
 	}
 }
 
@@ -84,3 +88,6 @@ func Fadvise(f *os.File, off, len int64, advice FadviseAdvice) error {
 		0, 0)
 	return os.NewSyscallError("SYS_FADVISE64", errno)
 }
+
+// IsEOF reports whether err is an EOF condition.
+func IsEOF(err error) bool { return err == io.EOF }

third_party/github.com/cznic/fileutil/fileutil_windows.go

@@ -5,7 +5,9 @@
 package fileutil
 
 import (
+	"io"
 	"os"
+	"syscall"
 )
 
 // PunchHole deallocates space inside a file in the byte range starting at
@@ -19,3 +21,14 @@ func PunchHole(f *os.File, off, len int64) error {
 func Fadvise(f *os.File, off, len int64, advice FadviseAdvice) error {
 	return nil
 }
+
+// IsEOF reports whether err is an EOF condition.
+func IsEOF(err error) bool {
+	if err == io.EOF {
+		return true
+	}
+
+	// http://social.technet.microsoft.com/Forums/windowsserver/en-US/1a16311b-c625-46cf-830b-6a26af488435/how-to-solve-error-38-0x26-errorhandleeof-using-fsctlgetretrievalpointers
+	x, ok := err.(*os.PathError)
+	return ok && x.Op == "read" && x.Err.(syscall.Errno) == 0x26
+}

third_party/github.com/cznic/fileutil/storage/probe_test.go

@@ -38,6 +38,7 @@ func (p *Probe) assert(t *testing.T, msg int, opsRd, opsWr, bytesRd, bytesWr, se
 }
 
 func TestProbe(t *testing.T) {
+	return //TODO disabled due to atomic.AddInt64 failing on W32
 	const fn = "test.tmp"
 
 	store, err := NewFile(fn, os.O_CREATE|os.O_RDWR|os.O_CREATE, 0666)

third_party/github.com/cznic/kv/all_test.go

@@ -8,15 +8,17 @@ import (
 	"encoding/binary"
 	"flag"
 	"fmt"
-	"io"
+	"io/ioutil"
 	"math"
 	"os"
 	"path"
+	"path/filepath"
 	"runtime"
 	"strings"
 	"sync"
 	"testing"
 
+	"camlistore.org/third_party/github.com/cznic/fileutil"
 	"camlistore.org/third_party/github.com/cznic/mathutil"
 )
 
@@ -146,9 +148,9 @@ func TestName(t *testing.T) {
 	}(db.Name())
 
 	if n := db.Name(); n == "" ||
-		!strings.Contains(n, "_testdata/") ||
-		!strings.HasPrefix(path.Base(n), "temp") ||
-		!strings.HasSuffix(path.Base(n), ".db") ||
+		!strings.Contains(n, "_testdata") ||
+		!strings.HasPrefix(filepath.Base(n), "temp") ||
+		!strings.HasSuffix(filepath.Base(n), ".db") ||
 		path.Base(n) == "temp.db" {
 		t.Error(n)
 	}
@@ -1393,7 +1395,7 @@ func TestSeekNext(t *testing.T) {
 
 				k, v, err := en.Next()
 				if err != nil {
-					if err != io.EOF {
+					if !fileutil.IsEOF(err) {
 						t.Fatal(i, err)
 					}
 
@@ -1487,7 +1489,7 @@ func TestSeekPrev(t *testing.T) {
 
 				k, v, err := en.Prev()
 				if err != nil {
-					if err != io.EOF {
+					if !fileutil.IsEOF(err) {
 						t.Fatal(i, err)
 					}
 
@@ -1808,3 +1810,64 @@ func TestWALName(t *testing.T) {
 		t.Error(n)
 	}
 }
+
+func TestCreateWithEmptyWAL(t *testing.T) {
+	dir, err := ioutil.TempDir("", "kv-test-create")
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	defer os.RemoveAll(dir)
+	dbName := filepath.Join(dir, "test.db")
+	var o Options
+	walName := o.walName(dbName, "")
+	wal, err := os.Create(walName)
+	if err != nil {
+		t.Error(err)
+		return
+	}
+
+	wal.Close()
+	defer os.Remove(walName)
+
+	db, err := Create(dbName, &Options{})
+	if err != nil {
+		t.Error(err)
+		return
+	}
+
+	if err = db.Set([]byte("foo"), []byte("bar")); err != nil {
+		t.Error(err)
+	}
+	db.Close()
+}
+
+func TestCreateWithNonEmptyWAL(t *testing.T) {
+	dir, err := ioutil.TempDir("", "kv-test-create")
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	defer os.RemoveAll(dir)
+	dbName := filepath.Join(dir, "test.db")
+	var o Options
+	walName := o.walName(dbName, "")
+	wal, err := os.Create(walName)
+	if err != nil {
+		t.Error(err)
+		return
+	}
+
+	if n, err := wal.Write([]byte{0}); n != 1 || err != nil {
+		t.Error(n, err)
+		return
+	}
+
+	wal.Close()
+	defer os.Remove(walName)
+
+	if _, err = Create(dbName, &Options{}); err == nil {
+		t.Error("Unexpected success")
+		return
+	}
+}

third_party/github.com/cznic/kv/etc.go

@@ -7,7 +7,8 @@ package kv
 import (
 	"bytes"
 	"fmt"
-	"io"
+
+	"camlistore.org/third_party/github.com/cznic/fileutil"
 )
 
 type header struct {
@@ -48,7 +49,7 @@ func h2b(b []byte, h int64) []byte {
 }
 
 func noEof(e error) (err error) {
-	if e != io.EOF {
+	if !fileutil.IsEOF(e) {
 		err = e
 	}
 	return

third_party/github.com/cznic/kv/kv.go

@@ -291,6 +291,13 @@ func (db *DB) Close() (err error) {
 			err = e1
 		}
 	}
+	if wal := db.wal; wal != nil {
+		e := wal.Close()
+		db.wal = nil
+		if err == nil {
+			err = e
+		}
+	}
 	return
 }
 
@@ -664,12 +671,10 @@ func (db *DB) Put(dst, key []byte, upd func(key, old []byte) (new []byte, write
 	return
 }
 
-// Seek returns an enumerator or an error if any. Normally the enumerator is
-// positioned on a KV pair such that 'key' >= KV.key and 'hit' is key ==
-// KV.key.  If 'key' collates after any existing key in the DB then the
-// enumerator's position is effectively "after" the last KV pair, but that is
-// not an error.  However, such enumerator will return err set to io.EOF from
-// its Next/Prev methods.
+// Seek returns an enumerator positioned on the first key/value pair whose key
+// is 'greater than or equal to' the given key. There may be no such pair, in
+// which case the Next,Prev methods of the returned enumerator will always
+// return io.EOF.
 //
 // Seek is atomic and it is safe for concurrent use by multiple goroutines.
 func (db *DB) Seek(key []byte) (enum *Enumerator, hit bool, err error) {

third_party/github.com/cznic/kv/options.go

@@ -85,8 +85,9 @@ type Options struct {
 	// used. If it is of zero size then a clean shutdown of the DB is
 	// assumed, otherwise an automatic DB recovery is performed.
 	//
-	// On creating a new DB the WAL file must not exist. It's not safe to
-	// write to a WAL file as it may contain unprocessed DB recovery data.
+	// On creating a new DB the WAL file must not exist or it must be
+	// empty. It's not safe to write to a non empty WAL file as it may
+	// contain unprocessed DB recovery data.
 	_WAL string
 
 	// Time to collect transactions before committing them into the WAL.
@@ -142,7 +143,16 @@ func (o *Options) check(dbname string, new, lock bool) (err error) {
 		case true:
 			if o.wal, err = os.OpenFile(o._WAL, os.O_CREATE|os.O_EXCL|os.O_RDWR, 0666); err != nil {
 				if os.IsExist(err) {
-					err = fmt.Errorf("cannot create DB %q: WAL file %q exists", dbname, o._WAL)
+					fi, e := os.Stat(o._WAL)
+					if e != nil {
+						return e
+					}
+
+					if sz := fi.Size(); sz != 0 {
+						return fmt.Errorf("cannot create DB %q: non empty WAL file %q (size %d) exists", dbname, o._WAL, sz)
+					}
+
+					o.wal, err = os.OpenFile(o._WAL, os.O_RDWR, 0666)
 				}
 				return
 			}