lib/db: Correct metadata recalculation (fixes #6381) (#6382)

If we decide to recalculate the metadata we shouldn't start from
whatever we loaded from the database, as that data is wrong. We should
start from a clean slate.

lib/db/meta_test.go

@@ -11,6 +11,8 @@ import (
 	"sort"
 	"testing"
 
+	"github.com/syncthing/syncthing/lib/db/backend"
+	"github.com/syncthing/syncthing/lib/fs"
 	"github.com/syncthing/syncthing/lib/protocol"
 )
 
@@ -101,3 +103,75 @@ func TestMetaSequences(t *testing.T) {
 		t.Error("sequence of first device should be 4, not", seq)
 	}
 }
+
+func TestRecalcMeta(t *testing.T) {
+	ldb := NewLowlevel(backend.OpenMemory())
+	defer ldb.Close()
+
+	// Add some files
+	s1 := NewFileSet("test", fs.NewFilesystem(fs.FilesystemTypeFake, "fake"), ldb)
+	files := []protocol.FileInfo{
+		{Name: "a", Size: 1000},
+		{Name: "b", Size: 2000},
+	}
+	s1.Update(protocol.LocalDeviceID, files)
+
+	// Verify local/global size
+	snap := s1.Snapshot()
+	ls := snap.LocalSize()
+	gs := snap.GlobalSize()
+	snap.Release()
+	if ls.Bytes != 3000 {
+		t.Fatalf("Wrong initial local byte count, %d != 3000", ls.Bytes)
+	}
+	if gs.Bytes != 3000 {
+		t.Fatalf("Wrong initial global byte count, %d != 3000", gs.Bytes)
+	}
+
+	// Reach into the database to make the metadata tracker intentionally
+	// wrong and out of date
+	curSeq := s1.meta.Sequence(protocol.LocalDeviceID)
+	tran, err := ldb.newReadWriteTransaction()
+	if err != nil {
+		t.Fatal(err)
+	}
+	s1.meta.mut.Lock()
+	s1.meta.countsPtr(protocol.LocalDeviceID, 0).Sequence = curSeq - 1 // too low
+	s1.meta.countsPtr(protocol.LocalDeviceID, 0).Bytes = 1234          // wrong
+	s1.meta.countsPtr(protocol.GlobalDeviceID, 0).Bytes = 1234         // wrong
+	s1.meta.dirty = true
+	s1.meta.mut.Unlock()
+	if err := s1.meta.toDB(tran, []byte("test")); err != nil {
+		t.Fatal(err)
+	}
+	if err := tran.Commit(); err != nil {
+		t.Fatal(err)
+	}
+
+	// Verify that our bad data "took"
+	snap = s1.Snapshot()
+	ls = snap.LocalSize()
+	gs = snap.GlobalSize()
+	snap.Release()
+	if ls.Bytes != 1234 {
+		t.Fatalf("Wrong changed local byte count, %d != 1234", ls.Bytes)
+	}
+	if gs.Bytes != 1234 {
+		t.Fatalf("Wrong changed global byte count, %d != 1234", gs.Bytes)
+	}
+
+	// Create a new fileset, which will realize the inconsistency and recalculate
+	s2 := NewFileSet("test", fs.NewFilesystem(fs.FilesystemTypeFake, "fake"), ldb)
+
+	// Verify local/global size
+	snap = s2.Snapshot()
+	ls = snap.LocalSize()
+	gs = snap.GlobalSize()
+	snap.Release()
+	if ls.Bytes != 3000 {
+		t.Fatalf("Wrong fixed local byte count, %d != 3000", ls.Bytes)
+	}
+	if gs.Bytes != 3000 {
+		t.Fatalf("Wrong fixed global byte count, %d != 3000", gs.Bytes)
+	}
+}

lib/db/set.go

@@ -81,10 +81,9 @@ func NewFileSet(folder string, fs fs.Filesystem, db *Lowlevel) *FileSet {
 }
 
 func loadMetadataTracker(db *Lowlevel, folder string) *metadataTracker {
-	meta := newMetadataTracker()
-
 	recalc := func() *metadataTracker {
-		if err := recalcMeta(meta, db, folder); backend.IsClosed(err) {
+		meta, err := recalcMeta(db, folder)
+		if backend.IsClosed(err) {
 			return nil
 		} else if err != nil {
 			panic(err)
@@ -92,12 +91,14 @@ func loadMetadataTracker(db *Lowlevel, folder string) *metadataTracker {
 		return meta
 	}
 
+	meta := newMetadataTracker()
 	if err := meta.fromDB(db, []byte(folder)); err != nil {
 		l.Infof("No stored folder metadata for %q; recalculating", folder)
 		return recalc()
 	}
 
-	if metaOK := verifyLocalSequence(meta, db, folder); !metaOK {
+	curSeq := meta.Sequence(protocol.LocalDeviceID)
+	if metaOK := verifyLocalSequence(curSeq, db, folder); !metaOK {
 		l.Infof("Stored folder metadata for %q is out of date after crash; recalculating", folder)
 		return recalc()
 	}
@@ -110,14 +111,15 @@ func loadMetadataTracker(db *Lowlevel, folder string) *metadataTracker {
 	return meta
 }
 
-func recalcMeta(meta *metadataTracker, db *Lowlevel, folder string) error {
+func recalcMeta(db *Lowlevel, folder string) (*metadataTracker, error) {
+	meta := newMetadataTracker()
 	if err := db.checkGlobals([]byte(folder), meta); err != nil {
-		return err
+		return nil, err
 	}
 
 	t, err := db.newReadWriteTransaction()
 	if err != nil {
-		return err
+		return nil, err
 	}
 	defer t.close()
 
@@ -128,19 +130,22 @@ func recalcMeta(meta *metadataTracker, db *Lowlevel, folder string) error {
 		return true
 	})
 	if err != nil {
-		return err
+		return nil, err
 	}
 
 	meta.SetCreated()
 	if err := meta.toDB(t, []byte(folder)); err != nil {
-		return err
+		return nil, err
+	}
+	if err := t.Commit(); err != nil {
+		return nil, err
 	}
-	return t.Commit()
+	return meta, nil
 }
 
 // Verify the local sequence number from actual sequence entries. Returns
 // true if it was all good, or false if a fixup was necessary.
-func verifyLocalSequence(meta *metadataTracker, db *Lowlevel, folder string) bool {
+func verifyLocalSequence(curSeq int64, db *Lowlevel, folder string) bool {
 	// Walk the sequence index from the current (supposedly) highest
 	// sequence number and raise the alarm if we get anything. This recovers
 	// from the occasion where we have written sequence entries to disk but
@@ -151,8 +156,6 @@ func verifyLocalSequence(meta *metadataTracker, db *Lowlevel, folder string) boo
 	// number than we've actually seen and receive some duplicate updates
 	// and then be in sync again.
 
-	curSeq := meta.Sequence(protocol.LocalDeviceID)
-
 	t, err := db.newReadOnlyTransaction()
 	if err != nil {
 		panic(err)