retry: limit retries based on elapsed time not count

Depending on how long an operation takes to fail, the total retry
duration can currently vary between 1.5 and 15 minutes. In particular
for temporarily interrupted network connections, the former timeout is
too short. Thus always use a limit of 15 minutes.

cmd/restic/global.go

@@ -425,7 +425,7 @@ func OpenRepository(ctx context.Context, opts GlobalOptions) (*repository.Reposi
 	success := func(msg string, retries int) {
 		Warnf("%v operation successful after %d retries\n", msg, retries)
 	}
-	be = retry.New(be, 10, report, success)
+	be = retry.New(be, 15*time.Minute, report, success)
 
 	// wrap backend if a test specified a hook
 	if opts.backendTestHook != nil {

internal/backend/retry/backend_retry.go

@@ -18,9 +18,9 @@ import (
 // backoff.
 type Backend struct {
 	backend.Backend
-	MaxTries int
-	Report   func(string, error, time.Duration)
-	Success  func(string, int)
+	MaxElapsedTime time.Duration
+	Report         func(string, error, time.Duration)
+	Success        func(string, int)
 
 	failedLoads sync.Map
 }
@@ -32,12 +32,12 @@ var _ backend.Backend = &Backend{}
 // backoff. report is called with a description and the error, if one occurred.
 // success is called with the number of retries before a successful operation
 // (it is not called if it succeeded on the first try)
-func New(be backend.Backend, maxTries int, report func(string, error, time.Duration), success func(string, int)) *Backend {
+func New(be backend.Backend, maxElapsedTime time.Duration, report func(string, error, time.Duration), success func(string, int)) *Backend {
 	return &Backend{
-		Backend:  be,
-		MaxTries: maxTries,
-		Report:   report,
-		Success:  success,
+		Backend:        be,
+		MaxElapsedTime: maxElapsedTime,
+		Report:         report,
+		Success:        success,
 	}
 }
 
@@ -82,9 +82,15 @@ func (be *Backend) retry(ctx context.Context, msg string, f func() error) error
 	}
 
 	bo := backoff.NewExponentialBackOff()
+	bo.MaxElapsedTime = be.MaxElapsedTime
+
 	if fastRetries {
 		// speed up integration tests
 		bo.InitialInterval = 1 * time.Millisecond
+		maxElapsedTime := 200 * time.Millisecond
+		if bo.MaxElapsedTime > maxElapsedTime {
+			bo.MaxElapsedTime = maxElapsedTime
+		}
 	}
 
 	err := retryNotifyErrorWithSuccess(
@@ -97,7 +103,7 @@ func (be *Backend) retry(ctx context.Context, msg string, f func() error) error
 			}
 			return err
 		},
-		backoff.WithContext(backoff.WithMaxRetries(bo, uint64(be.MaxTries)), ctx),
+		backoff.WithContext(bo, ctx),
 		func(err error, d time.Duration) {
 			if be.Report != nil {
 				be.Report(msg, err, d)

internal/backend/retry/backend_retry_test.go

@@ -193,8 +193,9 @@ func TestBackendListRetryErrorBackend(t *testing.T) {
 	}
 
 	TestFastRetries(t)
-	const maxRetries = 2
-	retryBackend := New(be, maxRetries, nil, nil)
+	const maxElapsedTime = 10 * time.Millisecond
+	now := time.Now()
+	retryBackend := New(be, maxElapsedTime, nil, nil)
 
 	var listed []string
 	err := retryBackend.List(context.TODO(), backend.PackFile, func(fi backend.FileInfo) error {
@@ -207,8 +208,9 @@ func TestBackendListRetryErrorBackend(t *testing.T) {
 		t.Fatalf("wrong error returned, want %v, got %v", ErrBackendTest, err)
 	}
 
-	if retries != maxRetries+1 {
-		t.Fatalf("List was called %d times, wanted %v", retries, maxRetries+1)
+	duration := time.Since(now)
+	if duration > 100*time.Millisecond {
+		t.Fatalf("list retries took %v, expected at most 10ms", duration)
 	}
 
 	test.Equals(t, names[:2], listed)