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// Copyright 2016 Google LLC
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// See the License for the specific language governing permissions and
// limitations under the License.
package internal
import (
gax ""
// Retry calls the supplied function f repeatedly according to the provided
// backoff parameters. It returns when one of the following occurs:
// When f's first return value is true, Retry immediately returns with f's second
// return value.
// When the provided context is done, Retry returns with an error that
// includes both ctx.Error() and the last error returned by f.
func Retry(ctx context.Context, bo gax.Backoff, f func() (stop bool, err error)) error {
return retry(ctx, bo, f, gax.Sleep)
func retry(ctx context.Context, bo gax.Backoff, f func() (stop bool, err error),
sleep func(context.Context, time.Duration) error) error {
var lastErr error
for {
stop, err := f()
if stop {
return err
// Remember the last "real" error from f.
if err != nil && err != context.Canceled && err != context.DeadlineExceeded {
lastErr = err
p := bo.Pause()
if ctxErr := sleep(ctx, p); ctxErr != nil {
if lastErr != nil {
return wrappedCallErr{ctxErr: ctxErr, wrappedErr: lastErr}
return ctxErr
// Use this error type to return an error which allows introspection of both
// the context error and the error from the service.
type wrappedCallErr struct {
ctxErr error
wrappedErr error
func (e wrappedCallErr) Error() string {
return fmt.Sprintf("retry failed with %v; last error: %v", e.ctxErr, e.wrappedErr)
func (e wrappedCallErr) Unwrap() error {
return e.wrappedErr
// Is allows errors.Is to match the error from the call as well as context
// sentinel errors.
func (e wrappedCallErr) Is(err error) bool {
return e.ctxErr == err || e.wrappedErr == err
// GRPCStatus allows the wrapped error to be used with status.FromError.
func (e wrappedCallErr) GRPCStatus() *status.Status {
if s, ok := status.FromError(e.wrappedErr); ok {
return s
return nil