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/*
*
* Copyright 2023 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
*
* https://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*
*/
// Package retry provides a retry helper for talking to S2A gRPC server.
// The implementation is modeled after
// https://github.com/googleapis/google-cloud-go/blob/main/compute/metadata/retry.go
package retry
import (
"context"
"math/rand"
"time"
"google.golang.org/grpc/grpclog"
)
const (
maxRetryAttempts = 5
maxRetryForLoops = 10
)
type defaultBackoff struct {
max time.Duration
mul float64
cur time.Duration
}
// Pause returns a duration, which is used as the backoff wait time
// before the next retry.
func (b *defaultBackoff) Pause() time.Duration {
d := time.Duration(1 + rand.Int63n(int64(b.cur)))
b.cur = time.Duration(float64(b.cur) * b.mul)
if b.cur > b.max {
b.cur = b.max
}
return d
}
// Sleep will wait for the specified duration or return on context
// expiration.
func Sleep(ctx context.Context, d time.Duration) error {
t := time.NewTimer(d)
select {
case <-ctx.Done():
t.Stop()
return ctx.Err()
case <-t.C:
return nil
}
}
// NewRetryer creates an instance of S2ARetryer using the defaultBackoff
// implementation.
var NewRetryer = func() *S2ARetryer {
return &S2ARetryer{bo: &defaultBackoff{
cur: 100 * time.Millisecond,
max: 30 * time.Second,
mul: 2,
}}
}
type backoff interface {
Pause() time.Duration
}
// S2ARetryer implements a retry helper for talking to S2A gRPC server.
type S2ARetryer struct {
bo backoff
attempts int
}
// Attempts return the number of retries attempted.
func (r *S2ARetryer) Attempts() int {
return r.attempts
}
// Retry returns a boolean indicating whether retry should be performed
// and the backoff duration.
func (r *S2ARetryer) Retry(err error) (time.Duration, bool) {
if err == nil {
return 0, false
}
if r.attempts >= maxRetryAttempts {
return 0, false
}
r.attempts++
return r.bo.Pause(), true
}
// Run uses S2ARetryer to execute the function passed in, until success or reaching
// max number of retry attempts.
func Run(ctx context.Context, f func() error) {
retryer := NewRetryer()
forLoopCnt := 0
var err error
for {
err = f()
if bo, shouldRetry := retryer.Retry(err); shouldRetry {
if grpclog.V(1) {
grpclog.Infof("will attempt retry: %v", err)
}
if ctx.Err() != nil {
if grpclog.V(1) {
grpclog.Infof("exit retry loop due to context error: %v", ctx.Err())
}
break
}
if errSleep := Sleep(ctx, bo); errSleep != nil {
if grpclog.V(1) {
grpclog.Infof("exit retry loop due to sleep error: %v", errSleep)
}
break
}
// This shouldn't happen, just make sure we are not stuck in the for loops.
forLoopCnt++
if forLoopCnt > maxRetryForLoops {
if grpclog.V(1) {
grpclog.Infof("exit the for loop after too many retries")
}
break
}
continue
}
if grpclog.V(1) {
grpclog.Infof("retry conditions not met, exit the loop")
}
break
}
}
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