cloudflare/cloudflared
Publicmirrored from https://github.com/cloudflare/cloudflaredAvailable
origin/backoffhandler.go
95lines · modecode
| 1 | package origin |
| 2 | |
| 3 | import ( |
| 4 | "time" |
| 5 | |
| 6 | "golang.org/x/net/context" |
| 7 | ) |
| 8 | |
| 9 | // Redeclare time functions so they can be overridden in tests. |
| 10 | var ( |
| 11 | timeNow = time.Now |
| 12 | timeAfter = time.After |
| 13 | ) |
| 14 | |
| 15 | // BackoffHandler manages exponential backoff and limits the maximum number of retries. |
| 16 | // The base time period is 1 second, doubling with each retry. |
| 17 | // After initial success, a grace period can be set to reset the backoff timer if |
| 18 | // a connection is maintained successfully for a long enough period. The base grace period |
| 19 | // is 2 seconds, doubling with each retry. |
| 20 | type BackoffHandler struct { |
| 21 | // MaxRetries sets the maximum number of retries to perform. The default value |
| 22 | // of 0 disables retry completely. |
| 23 | MaxRetries uint |
| 24 | // RetryForever caps the exponential backoff period according to MaxRetries |
| 25 | // but allows you to retry indefinitely. |
| 26 | RetryForever bool |
| 27 | // BaseTime sets the initial backoff period. |
| 28 | BaseTime time.Duration |
| 29 | |
| 30 | retries uint |
| 31 | resetDeadline time.Time |
| 32 | } |
| 33 | |
| 34 | func (b BackoffHandler) GetBackoffDuration(ctx context.Context) (time.Duration, bool) { |
| 35 | // Follows the same logic as Backoff, but without mutating the receiver. |
| 36 | // This select has to happen first to reflect the actual behaviour of the Backoff function. |
| 37 | select { |
| 38 | case <-ctx.Done(): |
| 39 | return time.Duration(0), false |
| 40 | default: |
| 41 | } |
| 42 | if !b.resetDeadline.IsZero() && timeNow().After(b.resetDeadline) { |
| 43 | // b.retries would be set to 0 at this point |
| 44 | return time.Second, true |
| 45 | } |
| 46 | if b.retries >= b.MaxRetries && !b.RetryForever { |
| 47 | return time.Duration(0), false |
| 48 | } |
| 49 | return time.Duration(b.GetBaseTime() * 1 << b.retries), true |
| 50 | } |
| 51 | |
| 52 | // BackoffTimer returns a channel that sends the current time when the exponential backoff timeout expires. |
| 53 | // Returns nil if the maximum number of retries have been used. |
| 54 | func (b *BackoffHandler) BackoffTimer() <-chan time.Time { |
| 55 | if !b.resetDeadline.IsZero() && timeNow().After(b.resetDeadline) { |
| 56 | b.retries = 0 |
| 57 | b.resetDeadline = time.Time{} |
| 58 | } |
| 59 | if b.retries >= b.MaxRetries { |
| 60 | if !b.RetryForever { |
| 61 | return nil |
| 62 | } |
| 63 | } else { |
| 64 | b.retries++ |
| 65 | } |
| 66 | return timeAfter(time.Duration(b.GetBaseTime() * 1 << (b.retries - 1))) |
| 67 | } |
| 68 | |
| 69 | // Backoff is used to wait according to exponential backoff. Returns false if the |
| 70 | // maximum number of retries have been used or if the underlying context has been cancelled. |
| 71 | func (b *BackoffHandler) Backoff(ctx context.Context) bool { |
| 72 | c := b.BackoffTimer() |
| 73 | if c == nil { |
| 74 | return false |
| 75 | } |
| 76 | select { |
| 77 | case <-c: |
| 78 | return true |
| 79 | case <-ctx.Done(): |
| 80 | return false |
| 81 | } |
| 82 | } |
| 83 | |
| 84 | // Sets a grace period within which the the backoff timer is maintained. After the grace |
| 85 | // period expires, the number of retries & backoff duration is reset. |
| 86 | func (b *BackoffHandler) SetGracePeriod() { |
| 87 | b.resetDeadline = timeNow().Add(time.Duration(b.GetBaseTime() * 2 << b.retries)) |
| 88 | } |
| 89 | |
| 90 | func (b BackoffHandler) GetBaseTime() time.Duration { |
| 91 | if b.BaseTime == 0 { |
| 92 | return time.Second |
| 93 | } |
| 94 | return b.BaseTime |
| 95 | } |
| 96 | |