backend: Split RetryBackend into own package

The RetryBackend tests depend on the mock backend. When the Backend
interface is eventually split from the restic package, this will lead to
a dependency cycle between backend and backend/mock. Thus split the
RetryBackend into a separate package to avoid this problem.

cmd/restic/global.go

@@ -22,6 +22,7 @@ import (
 	"github.com/restic/restic/internal/backend/location"
 	"github.com/restic/restic/internal/backend/rclone"
 	"github.com/restic/restic/internal/backend/rest"
+	"github.com/restic/restic/internal/backend/retry"
 	"github.com/restic/restic/internal/backend/s3"
 	"github.com/restic/restic/internal/backend/sftp"
 	"github.com/restic/restic/internal/backend/swift"
@@ -445,7 +446,7 @@ 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 = backend.NewRetryBackend(be, 10, report, success)
+	be = retry.New(be, 10, report, success)
 
 	// wrap backend if a test specified a hook
 	if opts.backendTestHook != nil {

cmd/restic/integration_helpers_test.go

@@ -9,7 +9,7 @@ import (
 	"runtime"
 	"testing"
 
-	"github.com/restic/restic/internal/backend"
+	"github.com/restic/restic/internal/backend/retry"
 	"github.com/restic/restic/internal/options"
 	"github.com/restic/restic/internal/repository"
 	"github.com/restic/restic/internal/restic"
@@ -172,7 +172,7 @@ func withTestEnvironment(t testing.TB) (env *testEnvironment, cleanup func()) {
 
 	repository.TestUseLowSecurityKDFParameters(t)
 	restic.TestDisableCheckPolynomial(t)
-	backend.TestFastRetries(t)
+	retry.TestFastRetries(t)
 
 	tempdir, err := ioutil.TempDir(rtest.TestTempDir, "restic-test-")
 	rtest.OK(t, err)