Merge pull request #113 from benbjohnson/meta-checksum

Add meta page checksums.

db.go

@@ -105,7 +105,7 @@ func Open(path string, mode os.FileMode) (*DB, error) {
 		if _, err := db.file.ReadAt(buf[:], 0); err == nil {
 			m := db.pageInBuffer(buf[:], 0).meta()
 			if err := m.validate(); err != nil {
-				return nil, fmt.Errorf("meta error: %s", err)
+				return nil, fmt.Errorf("meta0 error: %s", err)
 			}
 			db.pageSize = int(m.pageSize)
 		}

db_test.go

@@ -117,10 +117,43 @@ func TestDBCorruptMeta0(t *testing.T) {
 
 		// Open the database.
 		_, err = Open(path, 0666)
-		assert.Equal(t, err, errors.New("meta error: invalid database"))
+		assert.Equal(t, err, errors.New("meta0 error: invalid database"))
 	})
 }
 
+// Ensure that a corrupt meta page checksum causes the open to fail.
+func TestDBMetaChecksumError(t *testing.T) {
+	for i := 0; i < 2; i++ {
+		withTempPath(func(path string) {
+			db, err := Open(path, 0600)
+			pageSize := db.pageSize
+			db.Update(func(tx *Tx) error {
+				return tx.CreateBucket("widgets")
+			})
+			db.Update(func(tx *Tx) error {
+				return tx.CreateBucket("woojits")
+			})
+			db.Close()
+
+			// Change a single byte in the meta page.
+			f, _ := os.OpenFile(path, os.O_RDWR|os.O_CREATE, 0600)
+			f.WriteAt([]byte{1}, int64((i*pageSize)+(pageHeaderSize+12)))
+			f.Sync()
+			f.Close()
+
+			// Reopen the database.
+			_, err = Open(path, 0600)
+			if assert.Error(t, err) {
+				if i == 0 {
+					assert.Equal(t, "meta0 error: checksum error", err.Error())
+				} else {
+					assert.Equal(t, "meta1 error: checksum error", err.Error())
+				}
+			}
+		})
+	}
+}
+
 // Ensure that a database cannot open a transaction when it's not open.
 func TestDBTxErrDatabaseNotOpen(t *testing.T) {
 	var db DB

meta.go

@@ -2,6 +2,8 @@ package bolt
 
 import (
 	"errors"
+	"hash/fnv"
+	"unsafe"
 )
 
 const magic uint32 = 0xED0CDAED
@@ -13,6 +15,9 @@ var (
 	// ErrVersionMismatch is returned when the data file was created with a
 	// different version of Bolt.
 	ErrVersionMismatch = errors.New("version mismatch")
+
+	// ErrChecksum is returned when either meta page checksum does not match.
+	ErrChecksum = errors.New("checksum error")
 )
 
 type meta struct {
@@ -24,11 +29,14 @@ type meta struct {
 	freelist pgid
 	pgid     pgid
 	txid     txid
+	checksum uint64
 }
 
 // validate checks the marker bytes and version of the meta page to ensure it matches this binary.
 func (m *meta) validate() error {
-	if m.magic != magic {
+	if m.checksum != 0 && m.checksum != m.sum64() {
+		return ErrChecksum
+	} else if m.magic != magic {
 		return ErrInvalid
 	} else if m.version != version {
 		return ErrVersionMismatch
@@ -38,13 +46,7 @@ func (m *meta) validate() error {
 
 // copy copies one meta object to another.
 func (m *meta) copy(dest *meta) {
-	dest.magic = m.magic
-	dest.version = m.version
-	dest.pageSize = m.pageSize
-	dest.buckets = m.buckets
-	dest.freelist = m.freelist
-	dest.pgid = m.pgid
-	dest.txid = m.txid
+	*dest = *m
 }
 
 // write writes the meta onto a page.
@@ -53,5 +55,15 @@ func (m *meta) write(p *page) {
 	p.id = pgid(m.txid % 2)
 	p.flags |= metaPageFlag
 
+	// Calculate the checksum.
+	m.checksum = m.sum64()
+
 	m.copy(p.meta())
 }
+
+// generates the checksum for the meta.
+func (m *meta) sum64() uint64 {
+	var h = fnv.New64a()
+	_, _ = h.Write((*[unsafe.Offsetof(meta{}.checksum)]byte)(unsafe.Pointer(m))[:])
+	return h.Sum64()
+}