sync: fix --cutoff-mode soft & cautious so it doesn't end the transfer early

Before ths fix --cutoff-mode soft and cautious would emit a Fatal
error which stopped the sync immediately.

This fix introduces a new error which is checked in the sync error
processing which stops the sync gracefully.

Fixes #4576

fs/accounting/accounting.go

@@ -26,6 +26,10 @@ var ErrorMaxTransferLimitReached = errors.New("Max transfer limit reached as set
 // transfer limit is reached.
 var ErrorMaxTransferLimitReachedFatal = fserrors.FatalError(ErrorMaxTransferLimitReached)
 
+// ErrorMaxTransferLimitReachedGraceful is returned from operations.Copy when the max
+// transfer limit is reached and a graceful stop is required.
+var ErrorMaxTransferLimitReachedGraceful = fserrors.NoRetryError(ErrorMaxTransferLimitReached)
+
 // Account limits and accounts for one transfer
 type Account struct {
 	stats *StatsInfo

fs/operations/operations.go

@@ -363,7 +363,7 @@ func Copy(ctx context.Context, f fs.Fs, dst fs.Object, remote string, src fs.Obj
 		actionTaken = "Copied (server side copy)"
 		if fs.Config.MaxTransfer >= 0 && (accounting.Stats(ctx).GetBytes() >= int64(fs.Config.MaxTransfer) ||
 			(fs.Config.CutoffMode == fs.CutoffModeCautious && accounting.Stats(ctx).GetBytesWithPending()+src.Size() >= int64(fs.Config.MaxTransfer))) {
-			return nil, accounting.ErrorMaxTransferLimitReachedFatal
+			return nil, accounting.ErrorMaxTransferLimitReachedGraceful
 		}
 		if doCopy := f.Features().Copy; doCopy != nil && (SameConfig(src.Fs(), f) || (SameRemoteType(src.Fs(), f) && f.Features().ServerSideAcrossConfigs)) {
 			in := tr.Account(ctx, nil) // account the transfer

fs/operations/operations_test.go

@@ -1440,7 +1440,7 @@ func TestCopyFileMaxTransfer(t *testing.T) {
 	err = operations.CopyFile(ctx, r.Fremote, r.Flocal, file3.Path, file3.Path)
 	require.NotNil(t, err)
 	assert.Contains(t, err.Error(), "Max transfer limit reached")
-	assert.True(t, fserrors.IsFatalError(err))
+	assert.True(t, fserrors.IsNoRetryError(err))
 	fstest.CheckItems(t, r.Flocal, file1, file2, file3, file4)
 	fstest.CheckItems(t, r.Fremote, file1)
 

fs/sync/sync.go

@@ -32,6 +32,8 @@ type syncCopyMove struct {
 	// internal state
 	ctx                    context.Context        // internal context for controlling go-routines
 	cancel                 func()                 // cancel the context
+	inCtx                  context.Context        // internal context for controlling march
+	inCancel               func()                 // cancel the march context
 	noTraverse             bool                   // if set don't traverse the dst
 	noCheckDest            bool                   // if set transfer all objects regardless without checking dst
 	noUnicodeNormalization bool                   // don't normalize unicode characters in filenames
@@ -144,6 +146,8 @@ func newSyncCopyMove(ctx context.Context, fdst, fsrc fs.Fs, deleteMode fs.Delete
 	} else {
 		s.ctx, s.cancel = context.WithCancel(ctx)
 	}
+	// Input context - cancel this for graceful stop
+	s.inCtx, s.inCancel = context.WithCancel(s.ctx)
 	if s.noTraverse && s.deleteMode != fs.DeleteModeOff {
 		fs.Errorf(nil, "Ignoring --no-traverse with sync")
 		s.noTraverse = false
@@ -248,6 +252,12 @@ func (s *syncCopyMove) processError(err error) {
 	}
 	if err == context.DeadlineExceeded {
 		err = fserrors.NoRetryError(err)
+	} else if err == accounting.ErrorMaxTransferLimitReachedGraceful {
+		if s.inCtx.Err() == nil {
+			fs.Logf(nil, "%v - stopping transfers", err)
+			// Cancel the march and stop the pipes
+			s.inCancel()
+		}
 	}
 	s.errorMu.Lock()
 	defer s.errorMu.Unlock()
@@ -287,7 +297,7 @@ func (s *syncCopyMove) currentError() error {
 func (s *syncCopyMove) pairChecker(in *pipe, out *pipe, fraction int, wg *sync.WaitGroup) {
 	defer wg.Done()
 	for {
-		pair, ok := in.GetMax(s.ctx, fraction)
+		pair, ok := in.GetMax(s.inCtx, fraction)
 		if !ok {
 			return
 		}
@@ -343,7 +353,7 @@ func (s *syncCopyMove) pairChecker(in *pipe, out *pipe, fraction int, wg *sync.W
 func (s *syncCopyMove) pairRenamer(in *pipe, out *pipe, fraction int, wg *sync.WaitGroup) {
 	defer wg.Done()
 	for {
-		pair, ok := in.GetMax(s.ctx, fraction)
+		pair, ok := in.GetMax(s.inCtx, fraction)
 		if !ok {
 			return
 		}
@@ -363,7 +373,7 @@ func (s *syncCopyMove) pairCopyOrMove(ctx context.Context, in *pipe, fdst fs.Fs,
 	defer wg.Done()
 	var err error
 	for {
-		pair, ok := in.GetMax(s.ctx, fraction)
+		pair, ok := in.GetMax(s.inCtx, fraction)
 		if !ok {
 			return
 		}
@@ -809,7 +819,7 @@ func (s *syncCopyMove) run() error {
 
 	// set up a march over fdst and fsrc
 	m := &march.March{
-		Ctx:                    s.ctx,
+		Ctx:                    s.inCtx,
 		Fdst:                   s.fdst,
 		Fsrc:                   s.fsrc,
 		Dir:                    s.dir,

fs/sync/sync_test.go

@@ -1851,27 +1851,32 @@ func TestSyncIgnoreCase(t *testing.T) {
 	fstest.CheckItems(t, r.Fremote, file2)
 }
 
-// Test that aborting on max upload works
+// Test that aborting on --max-transfer works
-func TestAbort(t *testing.T) {
+func TestMaxTransfer(t *testing.T) {
-	r := fstest.NewRun(t)
-	defer r.Finalise()
-
-	if r.Fremote.Name() != "local" {
-		t.Skip("This test only runs on local")
-	}
-
 	oldMaxTransfer := fs.Config.MaxTransfer
 	oldTransfers := fs.Config.Transfers
 	oldCheckers := fs.Config.Checkers
+	oldCutoff := fs.Config.CutoffMode
 	fs.Config.MaxTransfer = 3 * 1024
 	fs.Config.Transfers = 1
 	fs.Config.Checkers = 1
+	fs.Config.CutoffMode = fs.CutoffModeHard
 	defer func() {
 		fs.Config.MaxTransfer = oldMaxTransfer
 		fs.Config.Transfers = oldTransfers
 		fs.Config.Checkers = oldCheckers
+		fs.Config.CutoffMode = oldCutoff
 	}()
 
+	test := func(t *testing.T, cutoff fs.CutoffMode) {
+		r := fstest.NewRun(t)
+		defer r.Finalise()
+		fs.Config.CutoffMode = cutoff
+
+		if r.Fremote.Name() != "local" {
+			t.Skip("This test only runs on local")
+		}
+
 		// Create file on source
 		file1 := r.WriteFile("file1", string(make([]byte, 5*1024)), t1)
 		file2 := r.WriteFile("file2", string(make([]byte, 2*1024)), t1)
@@ -1883,6 +1888,14 @@ func TestAbort(t *testing.T) {
 
 		err := Sync(context.Background(), r.Fremote, r.Flocal, false)
 		expectedErr := fserrors.FsError(accounting.ErrorMaxTransferLimitReachedFatal)
+		if cutoff != fs.CutoffModeHard {
+			expectedErr = accounting.ErrorMaxTransferLimitReachedGraceful
+		}
 		fserrors.Count(expectedErr)
 		assert.Equal(t, expectedErr, err)
 	}
+
+	t.Run("Hard", func(t *testing.T) { test(t, fs.CutoffModeHard) })
+	t.Run("Soft", func(t *testing.T) { test(t, fs.CutoffModeSoft) })
+	t.Run("Cautious", func(t *testing.T) { test(t, fs.CutoffModeCautious) })
+}