http.go

// Copyright 2018 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

package acme

import (
	"bytes"
	"context"
	"crypto"
	"crypto/rand"
	"encoding/json"
	"errors"
	"fmt"
	"io"
	"math/big"
	"net/http"
	"strconv"
	"strings"
	"time"
)

// retryTimer encapsulates common logic for retrying unsuccessful requests.
// It is not safe for concurrent use.
type retryTimer struct {
	// backoffFn provides backoff delay sequence for retries.
	// See Client.RetryBackoff doc comment.
	backoffFn func(n int, r *http.Request, res *http.Response) time.Duration
	// n is the current retry attempt.
	n int
}

func (t *retryTimer) inc() {
	t.n++
}

// backoff pauses the current goroutine as described in Client.RetryBackoff.
func (t *retryTimer) backoff(ctx context.Context, r *http.Request, res *http.Response) error {
	d := t.backoffFn(t.n, r, res)
	if d <= 0 {
		return fmt.Errorf("acme: no more retries for %s; tried %d time(s)", r.URL, t.n)
	}
	wakeup := time.NewTimer(d)
	defer wakeup.Stop()
	select {
	case <-ctx.Done():
		return ctx.Err()
	case <-wakeup.C:
		return nil
	}
}

func (c *Client) retryTimer() *retryTimer {
	f := c.RetryBackoff
	if f == nil {
		f = defaultBackoff
	}
	return &retryTimer{backoffFn: f}
}

// defaultBackoff provides default Client.RetryBackoff implementation
// using a truncated exponential backoff algorithm,
// as described in Client.RetryBackoff.
//
// The n argument is always bounded between 1 and 30.
// The returned value is always greater than 0.
func defaultBackoff(n int, r *http.Request, res *http.Response) time.Duration {
	const max = 10 * time.Second
	var jitter time.Duration
	if x, err := rand.Int(rand.Reader, big.NewInt(1000)); err == nil {