add additional meta page tests

db.go

@@ -208,8 +208,10 @@ func Open(path string, mode os.FileMode, options *Options) (*DB, error) {
 				// If we can't read the page size, we can assume it's the same
 				// as the OS -- since that's how the page size was chosen in the
 				// first place.
-				// XXX: Does this cause issues with opening a database on a
-				//      different OS than the one it was created on?
+				//
+				// If the first page is invalid and this OS uses a different
+				// page size than what the database was created with then we
+				// are out of luck and cannot access the database.
 				db.pageSize = os.Getpagesize()
 			} else {
 				db.pageSize = int(m.pageSize)
@@ -286,7 +288,7 @@ func (db *DB) mmap(minsz int) error {
 	err0 := db.meta0.validate()
 	err1 := db.meta1.validate()
 	if err0 != nil && err1 != nil {
-		return fmt.Errorf("meta0(%v) meta1(%v)", err0, err1)
+		return err0
 	}
 
 	return nil
@@ -358,6 +360,7 @@ func (db *DB) init() error {
 		m.root = bucket{root: 3}
 		m.pgid = 4
 		m.txid = txid(i)
+		m.checksum = m.sum64()
 	}
 
 	// Write an empty freelist at page 3.
@@ -807,20 +810,16 @@ func (db *DB) meta() *meta {
 		metaB = db.meta0
 	}
 
-	errA := metaA.validate()
-	errB := metaB.validate()
-
-	if errA == nil {
+	// Use higher meta page if valid. Otherwise fallback to previous, if valid.
+	if err := metaA.validate(); err == nil {
 		return metaA
-	}
-
-	if errB == nil {
+	} else if err := metaB.validate(); err == nil {
 		return metaB
 	}
 
 	// This should never be reached, because both meta1 and meta0 were validated
 	// on mmap() and we do fsync() on every write.
-	panic("both meta0 and meta1 could not be validated in DB.meta()!")
+	panic("bolt.DB.meta(): invalid meta pages")
 }
 
 // allocate returns a contiguous block of memory starting at a given page.
@@ -981,12 +980,12 @@ type meta struct {
 
 // validate checks the marker bytes and version of the meta page to ensure it matches this binary.
 func (m *meta) validate() error {
-	if m.checksum != 0 && m.checksum != m.sum64() {
-		return ErrChecksum
-	} else if m.magic != magic {
+	if m.magic != magic {
 		return ErrInvalid
 	} else if m.version != version {
 		return ErrVersionMismatch
+	} else if m.checksum != 0 && m.checksum != m.sum64() {
+		return ErrChecksum
 	}
 	return nil
 }

db_test.go

@@ -45,7 +45,7 @@ type meta struct {
 	_        uint32
 	_        [16]byte
 	_        uint64
-	_        uint64
+	pgid     uint64
 	_        uint64
 	checksum uint64
 }
@@ -85,75 +85,97 @@ func TestOpen_ErrNotExists(t *testing.T) {
 	}
 }
 
-// Ensure that opening a file with wrong checksum returns ErrChecksum.
-func TestOpen_ErrChecksum(t *testing.T) {
-	buf := make([]byte, pageSize)
-	meta := (*meta)(unsafe.Pointer(&buf[0]))
-	meta.magic = magic
-	meta.version = version
-	meta.checksum = 123
-
+// Ensure that opening a file that is not a Bolt database returns ErrInvalid.
+func TestOpen_ErrInvalid(t *testing.T) {
 	path := tempfile()
+
 	f, err := os.Create(path)
 	if err != nil {
 		t.Fatal(err)
 	}
-	if _, err := f.WriteAt(buf, pageHeaderSize); err != nil {
+	if _, err := fmt.Fprintln(f, "this is not a bolt database"); err != nil {
 		t.Fatal(err)
 	}
 	if err := f.Close(); err != nil {
 		t.Fatal(err)
 	}
 	defer os.Remove(path)
 
-	if _, err := bolt.Open(path, 0666, nil); err != bolt.ErrChecksum {
+	if _, err := bolt.Open(path, 0666, nil); err != bolt.ErrInvalid {
 		t.Fatalf("unexpected error: %s", err)
 	}
 }
 
-// Ensure that opening a file that is not a Bolt database returns ErrInvalid.
-func TestOpen_ErrInvalid(t *testing.T) {
-	path := tempfile()
+// Ensure that opening a file with two invalid versions returns ErrVersionMismatch.
+func TestOpen_ErrVersionMismatch(t *testing.T) {
+	if pageSize != os.Getpagesize() {
+		t.Skip("page size mismatch")
+	}
 
-	f, err := os.Create(path)
-	if err != nil {
+	// Create empty database.
+	db := MustOpenDB()
+	path := db.Path()
+	defer db.MustClose()
+
+	// Close database.
+	if err := db.DB.Close(); err != nil {
 		t.Fatal(err)
 	}
-	if _, err := fmt.Fprintln(f, "this is not a bolt database"); err != nil {
+
+	// Read data file.
+	buf, err := ioutil.ReadFile(path)
+	if err != nil {
 		t.Fatal(err)
 	}
-	if err := f.Close(); err != nil {
+
+	// Rewrite meta pages.
+	meta0 := (*meta)(unsafe.Pointer(&buf[pageHeaderSize]))
+	meta0.version++
+	meta1 := (*meta)(unsafe.Pointer(&buf[pageSize+pageHeaderSize]))
+	meta1.version++
+	if err := ioutil.WriteFile(path, buf, 0666); err != nil {
 		t.Fatal(err)
 	}
-	defer os.Remove(path)
 
-	if _, err := bolt.Open(path, 0666, nil); err != bolt.ErrInvalid {
+	// Reopen data file.
+	if _, err := bolt.Open(path, 0666, nil); err != bolt.ErrVersionMismatch {
 		t.Fatalf("unexpected error: %s", err)
 	}
 }
 
-// Ensure that opening a file created with a different version of Bolt returns
-// ErrVersionMismatch.
-func TestOpen_ErrVersionMismatch(t *testing.T) {
-	buf := make([]byte, pageSize)
-	meta := (*meta)(unsafe.Pointer(&buf[0]))
-	meta.magic = magic
-	meta.version = version + 100
+// Ensure that opening a file with two invalid checksums returns ErrChecksum.
+func TestOpen_ErrChecksum(t *testing.T) {
+	if pageSize != os.Getpagesize() {
+		t.Skip("page size mismatch")
+	}
 
-	path := tempfile()
-	f, err := os.Create(path)
-	if err != nil {
+	// Create empty database.
+	db := MustOpenDB()
+	path := db.Path()
+	defer db.MustClose()
+
+	// Close database.
+	if err := db.DB.Close(); err != nil {
 		t.Fatal(err)
 	}
-	if _, err := f.WriteAt(buf, pageHeaderSize); err != nil {
+
+	// Read data file.
+	buf, err := ioutil.ReadFile(path)
+	if err != nil {
 		t.Fatal(err)
 	}
-	if err := f.Close(); err != nil {
+
+	// Rewrite meta pages.
+	meta0 := (*meta)(unsafe.Pointer(&buf[pageHeaderSize]))
+	meta0.pgid++
+	meta1 := (*meta)(unsafe.Pointer(&buf[pageSize+pageHeaderSize]))
+	meta1.pgid++
+	if err := ioutil.WriteFile(path, buf, 0666); err != nil {
 		t.Fatal(err)
 	}
-	defer os.Remove(path)
 
-	if _, err := bolt.Open(path, 0666, nil); err != bolt.ErrVersionMismatch {
+	// Reopen data file.
+	if _, err := bolt.Open(path, 0666, nil); err != bolt.ErrChecksum {
 		t.Fatalf("unexpected error: %s", err)
 	}
 }

errors.go

@@ -12,7 +12,8 @@ var (
 	// already open.
 	ErrDatabaseOpen = errors.New("database already open")
 
-	// ErrInvalid is returned when a data file is not a Bolt-formatted database.
+	// ErrInvalid is returned when both meta pages on a database are invalid.
+	// This typically occurs when a file is not a bolt database.
 	ErrInvalid = errors.New("invalid database")
 
 	// ErrVersionMismatch is returned when the data file was created with a