Update ai3/go-common

go.mod

@@ -3,7 +3,7 @@ module git.autistici.org/id/go-sso
 go 1.14
 
 require (
-	git.autistici.org/ai3/go-common v0.0.0-20210110180225-a05c683cfe23
+	git.autistici.org/ai3/go-common v0.0.0-20210118064555-73f00db54723
 	git.autistici.org/id/auth v0.0.0-20210110171913-dd493db32815
 	git.autistici.org/id/keystore v0.0.0-20210110165905-d5b171e81071
 	github.com/crewjam/saml v0.4.5

go.sum

@@ -3,8 +3,8 @@ cloud.google.com/go v0.34.0/go.mod h1:aQUYkXzVsufM+DwF1aE+0xfcU+56JwCaLick0ClmMT
 contrib.go.opencensus.io/exporter/zipkin v0.1.2 h1:YqE293IZrKtqPnpwDPH/lOqTWD/s3Iwabycam74JV3g=
 contrib.go.opencensus.io/exporter/zipkin v0.1.2/go.mod h1:mP5xM3rrgOjpn79MM8fZbj3gsxcuytSqtH0dxSWW1RE=
 git.autistici.org/ai3/go-common v0.0.0-20210109170950-49f8d26bcc81/go.mod h1:nuLJyKZZaC3DBPN4gA1qdGXcm0U5WCcus1z3pI8RdTE=
-git.autistici.org/ai3/go-common v0.0.0-20210110180225-a05c683cfe23 h1:YHSG7Vr8nPRmXa7tW2UR8kfzwerjA5GD+bI84nxq2kA=
-git.autistici.org/ai3/go-common v0.0.0-20210110180225-a05c683cfe23/go.mod h1:Iik+i0XmqNPTBjWl3vicFz0kjfFK5HBvyFsfIC4S1Ik=
+git.autistici.org/ai3/go-common v0.0.0-20210118064555-73f00db54723 h1:ylA6azCumIJnT7xb5hHrz0At6r1u3zqnugl1gB92KO0=
+git.autistici.org/ai3/go-common v0.0.0-20210118064555-73f00db54723/go.mod h1:T8BS+630KLzy30X2lshL98H0NW3Xuyzs8NI9D6C3New=
 git.autistici.org/id/auth v0.0.0-20210110171913-dd493db32815 h1:gjBHxd2voc+mqHKQqUxkgVqQWGlysWZKJFIRcINpI40=
 git.autistici.org/id/auth v0.0.0-20210110171913-dd493db32815/go.mod h1:Hq4zcqE2hbrXsC9j79kzfnBf2BqlGmuVCRIz+AwX/FY=
 git.autistici.org/id/go-sso v0.0.0-20181118174541-ad4e62357912/go.mod h1:B9omXX7rw0qgWdBoF4RZnM7clwEVejoAe8oNJWETBZ0=
@@ -46,6 +46,7 @@ github.com/bradfitz/gomemcache v0.0.0-20180710155616-bc664df96737/go.mod h1:PmM6
 github.com/casbin/casbin/v2 v2.1.2/go.mod h1:YcPU1XXisHhLzuxH9coDNf2FbKpjGlbCg3n9yuLkIJQ=
 github.com/cenkalti/backoff v2.2.1+incompatible h1:tNowT99t7UNflLxfYYSlKYsBpXdEet03Pg2g16Swow4=
 github.com/cenkalti/backoff v2.2.1+incompatible/go.mod h1:90ReRw6GdpyfrHakVjL/QHaoyV4aDUVVkXQJJJ3NXXM=
+github.com/cenkalti/backoff/v4 v4.1.0 h1:c8LkOFQTzuO0WBM/ae5HdGQuZPfPxp7lqBRwQRm4fSc=
 github.com/cenkalti/backoff/v4 v4.1.0/go.mod h1:scbssz8iZGpm3xbr14ovlUdkxfGXNInqkPWOWmG2CLw=
 github.com/census-instrumentation/opencensus-proto v0.2.1/go.mod h1:f6KPmirojxKA12rnyqOA5BBL4O983OfeGPqjHWSTneU=
 github.com/cespare/xxhash/v2 v2.1.1 h1:6MnRN8NT7+YBpUIWxHtefFZOKTAPgGjpQSxqLNn0+qY=
@@ -79,8 +80,6 @@ github.com/eapache/go-resiliency v1.1.0/go.mod h1:kFI+JgMyC7bLPUVY133qvEBtVayf5m
 github.com/eapache/go-xerial-snappy v0.0.0-20180814174437-776d5712da21/go.mod h1:+020luEh2TKB4/GOp8oxxtq0Daoen/Cii55CzbTV6DU=
 github.com/eapache/queue v1.1.0/go.mod h1:6eCeP0CKFpHLu8blIFXhExK/dRa7WDZfr6jVFPTqq+I=
 github.com/edsrzf/mmap-go v1.0.0/go.mod h1:YO35OhQPt3KJa3ryjFM5Bs14WD66h8eGKpfaBNrHW5M=
-github.com/elazarl/go-bindata-assetfs v1.0.0 h1:G/bYguwHIzWq9ZoyUQqrjTmJbbYn3j3CKKpKinvZLFk=
-github.com/elazarl/go-bindata-assetfs v1.0.0/go.mod h1:v+YaWX3bdea5J/mo8dSETolEo7R71Vk1u8bnjau5yw4=
 github.com/elazarl/go-bindata-assetfs v1.0.1 h1:m0kkaHRKEu7tUIUFVwhGGGYClXvyl4RE03qmvRTNfbw=
 github.com/elazarl/go-bindata-assetfs v1.0.1/go.mod h1:v+YaWX3bdea5J/mo8dSETolEo7R71Vk1u8bnjau5yw4=
 github.com/emersion/go-textwrapper v0.0.0-20200911093747-65d896831594/go.mod h1:aqO8z8wPrjkscevZJFVE1wXJrLpC5LtJG7fqLOsPb2U=
@@ -244,8 +243,6 @@ github.com/modern-go/concurrent v0.0.0-20180228061459-e0a39a4cb421/go.mod h1:6dJ
 github.com/modern-go/concurrent v0.0.0-20180306012644-bacd9c7ef1dd/go.mod h1:6dJC0mAP4ikYIbvyc7fijjWJddQyLn8Ig3JB5CqoB9Q=
 github.com/modern-go/reflect2 v0.0.0-20180701023420-4b7aa43c6742/go.mod h1:bx2lNnkwVCuqBIxFjflWJWanXIb3RllmbCylyMrvgv0=
 github.com/modern-go/reflect2 v1.0.1/go.mod h1:bx2lNnkwVCuqBIxFjflWJWanXIb3RllmbCylyMrvgv0=
-github.com/mssola/user_agent v0.0.0-20170906152553-a2f39d5a9b15 h1:54aZUqayqLAOVJ+qn8t/w3psE6g9iNL9zURF/S3Rdp4=
-github.com/mssola/user_agent v0.0.0-20170906152553-a2f39d5a9b15/go.mod h1:UFiKPVaShrJGW93n4uo8dpPdg1BSVpw2P9bneo0Mtp8=
 github.com/mssola/user_agent v0.5.2 h1:CZkTUahjL1+OcZ5zv3kZr8QiJ8jy2H08vZIEkBeRbxo=
 github.com/mssola/user_agent v0.5.2/go.mod h1:TTPno8LPY3wAIEKRpAtkdMT0f8SE24pLRGPahjCH4uw=
 github.com/mwitkow/go-conntrack v0.0.0-20161129095857-cc309e4a2223/go.mod h1:qRWi+5nqEBWmkhHvq77mSJWrCKwh8bxhgT7d/eI7P4U=
@@ -274,10 +271,6 @@ github.com/openzipkin/zipkin-go v0.2.1/go.mod h1:NaW6tEwdmWMaCDZzg8sh+IBNOxHMPnh
 github.com/openzipkin/zipkin-go v0.2.2/go.mod h1:NaW6tEwdmWMaCDZzg8sh+IBNOxHMPnhQw8ySjnjRyN4=
 github.com/openzipkin/zipkin-go v0.2.5 h1:UwtQQx2pyPIgWYHRg+epgdx1/HnBQTgN3/oIYEJTQzU=
 github.com/openzipkin/zipkin-go v0.2.5/go.mod h1:KpXfKdgRDnnhsxw4pNIH9Md5lyFqKUa4YDFlwRYAMyE=
-github.com/oschwald/maxminddb-golang v0.0.0-20170901134056-26fe5ace1c70 h1:XGLYUmodtNzThosQ8GkMvj9TiIB/uWsP8NfxKSa3aDc=
-github.com/oschwald/maxminddb-golang v0.0.0-20170901134056-26fe5ace1c70/go.mod h1:3jhIUymTJ5VREKyIhWm66LJiQt04F0UCDdodShpjWsY=
-github.com/oschwald/maxminddb-golang v0.2.0 h1:cdvE3VUWCRdu+tYIBtwbcPWj1A83jZc5CSdGSuhnqO8=
-github.com/oschwald/maxminddb-golang v0.2.0/go.mod h1:3jhIUymTJ5VREKyIhWm66LJiQt04F0UCDdodShpjWsY=
 github.com/oschwald/maxminddb-golang v1.8.0 h1:Uh/DSnGoxsyp/KYbY1AuP0tYEwfs0sCph9p/UMXK/Hk=
 github.com/oschwald/maxminddb-golang v1.8.0/go.mod h1:RXZtst0N6+FY/3qCNmZMBApR19cdQj43/NM9VkrNAis=
 github.com/pact-foundation/pact-go v1.0.4/go.mod h1:uExwJY4kCzNPcHRj+hCR/HBbOOIwwtUjcrb0b5/5kLM=
@@ -326,8 +319,6 @@ github.com/prometheus/procfs v0.2.0/go.mod h1:lV6e/gmhEcM9IjHGsFOCxxuZ+z1YqCvr4O
 github.com/rcrowley/go-metrics v0.0.0-20181016184325-3113b8401b8a/go.mod h1:bCqnVzQkZxMG4s8nGwiZ5l3QUCyqpo9Y+/ZMZ9VjZe4=
 github.com/rogpeppe/fastuuid v0.0.0-20150106093220-6724a57986af/go.mod h1:XWv6SoW27p1b0cqNHllgS5HIMJraePCO15w5zCzIWYg=
 github.com/rogpeppe/go-internal v1.3.0/go.mod h1:M8bDsm7K2OlrFYOpmOWEs/qY81heoFRclV5y23lUDJ4=
-github.com/rs/cors v0.0.0-20190613161432-33ffc0734c60 h1:aIKs9zU56w6dx+KY0YN5YmBxe+Kqx5cZuHTPxgHaYkc=
-github.com/rs/cors v0.0.0-20190613161432-33ffc0734c60/go.mod h1:gFx+x8UowdsKA9AchylcLynDq+nNFfI8FkUZdN/jGCU=
 github.com/rs/cors v1.7.0 h1:+88SsELBHx5r+hZ8TCkggzSstaWNbDvThkVK8H6f9ik=
 github.com/rs/cors v1.7.0/go.mod h1:gFx+x8UowdsKA9AchylcLynDq+nNFfI8FkUZdN/jGCU=
 github.com/russellhaering/goxmldsig v1.1.0 h1:lK/zeJie2sqG52ZAlPNn1oBBqsIsEKypUUBGpYYF6lk=

vendor/git.autistici.org/ai3/go-common/clientutil/balancer.go

@@ -16,7 +16,7 @@ import (
 	"strings"
 	"time"
 
-	"github.com/cenkalti/backoff"
+	"github.com/cenkalti/backoff/v4"
 )
 
 // Our own narrow logger interface.

vendor/git.autistici.org/ai3/go-common/go.mod

@@ -6,7 +6,6 @@ require (
 	contrib.go.opencensus.io/exporter/zipkin v0.1.2
 	github.com/amoghe/go-crypt v0.0.0-20191109212615-b2ff80594b7f
 	github.com/bbrks/wrap/v2 v2.5.0
-	github.com/cenkalti/backoff v2.2.1+incompatible
 	github.com/cenkalti/backoff/v4 v4.1.0
 	github.com/coreos/go-systemd/v22 v22.1.0
 	github.com/emersion/go-textwrapper v0.0.0-20200911093747-65d896831594
@@ -17,16 +16,12 @@ require (
 	github.com/gorilla/handlers v1.5.1
 	github.com/lunixbochs/struc v0.0.0-20200707160740-784aaebc1d40
 	github.com/miscreant/miscreant.go v0.0.0-20200214223636-26d376326b75
-	github.com/modern-go/concurrent v0.0.0-20180306012644-bacd9c7ef1dd // indirect
 	github.com/openzipkin/zipkin-go v0.2.5
-	github.com/pierrec/lz4 v2.0.5+incompatible // indirect
 	github.com/prometheus/client_golang v1.9.0
 	github.com/russross/blackfriday/v2 v2.1.0
 	github.com/theckman/go-flock v0.8.0
 	github.com/tstranex/u2f v1.0.0
 	go.opencensus.io v0.22.5
 	golang.org/x/crypto v0.0.0-20201221181555-eec23a3978ad
-	golang.org/x/oauth2 v0.0.0-20190226205417-e64efc72b421 // indirect
 	golang.org/x/sync v0.0.0-20201207232520-09787c993a3a
-	gopkg.in/check.v1 v1.0.0-20190902080502-41f04d3bba15 // indirect
 )

vendor/git.autistici.org/ai3/go-common/go.sum

@@ -36,6 +36,7 @@ github.com/bgentry/speakeasy v0.1.0/go.mod h1:+zsyZBPWlz7T6j88CTgSN5bM796AkVf0kB
 github.com/casbin/casbin/v2 v2.1.2/go.mod h1:YcPU1XXisHhLzuxH9coDNf2FbKpjGlbCg3n9yuLkIJQ=
 github.com/cenkalti/backoff v2.2.1+incompatible h1:tNowT99t7UNflLxfYYSlKYsBpXdEet03Pg2g16Swow4=
 github.com/cenkalti/backoff v2.2.1+incompatible/go.mod h1:90ReRw6GdpyfrHakVjL/QHaoyV4aDUVVkXQJJJ3NXXM=
+github.com/cenkalti/backoff/v4 v4.1.0 h1:c8LkOFQTzuO0WBM/ae5HdGQuZPfPxp7lqBRwQRm4fSc=
 github.com/cenkalti/backoff/v4 v4.1.0/go.mod h1:scbssz8iZGpm3xbr14ovlUdkxfGXNInqkPWOWmG2CLw=
 github.com/census-instrumentation/opencensus-proto v0.2.1/go.mod h1:f6KPmirojxKA12rnyqOA5BBL4O983OfeGPqjHWSTneU=
 github.com/cespare/xxhash/v2 v2.1.1 h1:6MnRN8NT7+YBpUIWxHtefFZOKTAPgGjpQSxqLNn0+qY=

vendor/github.com/cenkalti/backoff/v4/.gitignore

+# Compiled Object files, Static and Dynamic libs (Shared Objects)
+*.o
+*.a
+*.so
+
+# Folders
+_obj
+_test
+
+# Architecture specific extensions/prefixes
+*.[568vq]
+[568vq].out
+
+*.cgo1.go
+*.cgo2.c
+_cgo_defun.c
+_cgo_gotypes.go
+_cgo_export.*
+
+_testmain.go
+
+*.exe
+
+# IDEs
+.idea/

vendor/github.com/cenkalti/backoff/v4/.travis.yml

+language: go
+go:
+  - 1.13
+  - 1.x
+  - tip
+before_install:
+  - go get github.com/mattn/goveralls
+  - go get golang.org/x/tools/cmd/cover
+script:
+  - $HOME/gopath/bin/goveralls -service=travis-ci

vendor/github.com/cenkalti/backoff/v4/LICENSE

+The MIT License (MIT)
+
+Copyright (c) 2014 Cenk Altı
+
+Permission is hereby granted, free of charge, to any person obtaining a copy of
+this software and associated documentation files (the "Software"), to deal in
+the Software without restriction, including without limitation the rights to
+use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of
+the Software, and to permit persons to whom the Software is furnished to do so,
+subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS
+FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR
+COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER
+IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
+CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.

vendor/github.com/cenkalti/backoff/v4/README.md

+# Exponential Backoff [![GoDoc][godoc image]][godoc] [![Build Status][travis image]][travis] [![Coverage Status][coveralls image]][coveralls]
+
+This is a Go port of the exponential backoff algorithm from [Google's HTTP Client Library for Java][google-http-java-client].
+
+[Exponential backoff][exponential backoff wiki]
+is an algorithm that uses feedback to multiplicatively decrease the rate of some process,
+in order to gradually find an acceptable rate.
+The retries exponentially increase and stop increasing when a certain threshold is met.
+
+## Usage
+
+Import path is `github.com/cenkalti/backoff/v4`. Please note the version part at the end.
+
+Use https://pkg.go.dev/github.com/cenkalti/backoff/v4 to view the documentation.
+
+## Contributing
+
+* I would like to keep this library as small as possible.
+* Please don't send a PR without opening an issue and discussing it first.
+* If proposed change is not a common use case, I will probably not accept it.
+
+[godoc]: https://pkg.go.dev/github.com/cenkalti/backoff/v4
+[godoc image]: https://godoc.org/github.com/cenkalti/backoff?status.png
+[travis]: https://travis-ci.org/cenkalti/backoff
+[travis image]: https://travis-ci.org/cenkalti/backoff.png?branch=master
+[coveralls]: https://coveralls.io/github/cenkalti/backoff?branch=master
+[coveralls image]: https://coveralls.io/repos/github/cenkalti/backoff/badge.svg?branch=master
+
+[google-http-java-client]: https://github.com/google/google-http-java-client/blob/da1aa993e90285ec18579f1553339b00e19b3ab5/google-http-client/src/main/java/com/google/api/client/util/ExponentialBackOff.java
+[exponential backoff wiki]: http://en.wikipedia.org/wiki/Exponential_backoff
+
+[advanced example]: https://pkg.go.dev/github.com/cenkalti/backoff/v4?tab=doc#pkg-examples

vendor/github.com/cenkalti/backoff/v4/backoff.go

+// Package backoff implements backoff algorithms for retrying operations.
+//
+// Use Retry function for retrying operations that may fail.
+// If Retry does not meet your needs,
+// copy/paste the function into your project and modify as you wish.
+//
+// There is also Ticker type similar to time.Ticker.
+// You can use it if you need to work with channels.
+//
+// See Examples section below for usage examples.
+package backoff
+
+import "time"
+
+// BackOff is a backoff policy for retrying an operation.
+type BackOff interface {
+	// NextBackOff returns the duration to wait before retrying the operation,
+	// or backoff. Stop to indicate that no more retries should be made.
+	//
+	// Example usage:
+	//
+	// 	duration := backoff.NextBackOff();
+	// 	if (duration == backoff.Stop) {
+	// 		// Do not retry operation.
+	// 	} else {
+	// 		// Sleep for duration and retry operation.
+	// 	}
+	//
+	NextBackOff() time.Duration
+
+	// Reset to initial state.
+	Reset()
+}
+
+// Stop indicates that no more retries should be made for use in NextBackOff().
+const Stop time.Duration = -1
+
+// ZeroBackOff is a fixed backoff policy whose backoff time is always zero,
+// meaning that the operation is retried immediately without waiting, indefinitely.
+type ZeroBackOff struct{}
+
+func (b *ZeroBackOff) Reset() {}
+
+func (b *ZeroBackOff) NextBackOff() time.Duration { return 0 }
+
+// StopBackOff is a fixed backoff policy that always returns backoff.Stop for
+// NextBackOff(), meaning that the operation should never be retried.
+type StopBackOff struct{}
+
+func (b *StopBackOff) Reset() {}
+
+func (b *StopBackOff) NextBackOff() time.Duration { return Stop }
+
+// ConstantBackOff is a backoff policy that always returns the same backoff delay.
+// This is in contrast to an exponential backoff policy,
+// which returns a delay that grows longer as you call NextBackOff() over and over again.
+type ConstantBackOff struct {
+	Interval time.Duration
+}
+
+func (b *ConstantBackOff) Reset()                     {}
+func (b *ConstantBackOff) NextBackOff() time.Duration { return b.Interval }
+
+func NewConstantBackOff(d time.Duration) *ConstantBackOff {
+	return &ConstantBackOff{Interval: d}
+}

vendor/github.com/cenkalti/backoff/v4/context.go

+package backoff
+
+import (
+	"context"
+	"time"
+)
+
+// BackOffContext is a backoff policy that stops retrying after the context
+// is canceled.
+type BackOffContext interface { // nolint: golint
+	BackOff
+	Context() context.Context
+}
+
+type backOffContext struct {
+	BackOff
+	ctx context.Context
+}
+
+// WithContext returns a BackOffContext with context ctx
+//
+// ctx must not be nil
+func WithContext(b BackOff, ctx context.Context) BackOffContext { // nolint: golint
+	if ctx == nil {
+		panic("nil context")
+	}
+
+	if b, ok := b.(*backOffContext); ok {
+		return &backOffContext{
+			BackOff: b.BackOff,
+			ctx:     ctx,
+		}
+	}
+
+	return &backOffContext{
+		BackOff: b,
+		ctx:     ctx,
+	}
+}
+
+func getContext(b BackOff) context.Context {
+	if cb, ok := b.(BackOffContext); ok {
+		return cb.Context()
+	}
+	if tb, ok := b.(*backOffTries); ok {
+		return getContext(tb.delegate)
+	}
+	return context.Background()
+}
+
+func (b *backOffContext) Context() context.Context {
+	return b.ctx
+}
+
+func (b *backOffContext) NextBackOff() time.Duration {
+	select {
+	case <-b.ctx.Done():
+		return Stop
+	default:
+	}
+	next := b.BackOff.NextBackOff()
+	if deadline, ok := b.ctx.Deadline(); ok && deadline.Sub(time.Now()) < next { // nolint: gosimple
+		return Stop
+	}
+	return next
+}

vendor/github.com/cenkalti/backoff/v4/exponential.go

+package backoff
+
+import (
+	"math/rand"
+	"time"
+)
+
+/*
+ExponentialBackOff is a backoff implementation that increases the backoff
+period for each retry attempt using a randomization function that grows exponentially.
+
+NextBackOff() is calculated using the following formula:
+
+ randomized interval =
+     RetryInterval * (random value in range [1 - RandomizationFactor, 1 + RandomizationFactor])
+
+In other words NextBackOff() will range between the randomization factor
+percentage below and above the retry interval.
+
+For example, given the following parameters:
+
+ RetryInterval = 2
+ RandomizationFactor = 0.5
+ Multiplier = 2
+
+the actual backoff period used in the next retry attempt will range between 1 and 3 seconds,
+multiplied by the exponential, that is, between 2 and 6 seconds.
+
+Note: MaxInterval caps the RetryInterval and not the randomized interval.
+
+If the time elapsed since an ExponentialBackOff instance is created goes past the
+MaxElapsedTime, then the method NextBackOff() starts returning backoff.Stop.
+
+The elapsed time can be reset by calling Reset().
+
+Example: Given the following default arguments, for 10 tries the sequence will be,
+and assuming we go over the MaxElapsedTime on the 10th try:
+
+ Request #  RetryInterval (seconds)  Randomized Interval (seconds)
+
+  1          0.5                     [0.25,   0.75]
+  2          0.75                    [0.375,  1.125]
+  3          1.125                   [0.562,  1.687]
+  4          1.687                   [0.8435, 2.53]
+  5          2.53                    [1.265,  3.795]
+  6          3.795                   [1.897,  5.692]
+  7          5.692                   [2.846,  8.538]
+  8          8.538                   [4.269, 12.807]
+  9         12.807                   [6.403, 19.210]
+ 10         19.210                   backoff.Stop
+
+Note: Implementation is not thread-safe.
+*/
+type ExponentialBackOff struct {
+	InitialInterval     time.Duration
+	RandomizationFactor float64
+	Multiplier          float64
+	MaxInterval         time.Duration
+	// After MaxElapsedTime the ExponentialBackOff returns Stop.
+	// It never stops if MaxElapsedTime == 0.
+	MaxElapsedTime time.Duration
+	Stop           time.Duration
+	Clock          Clock
+
+	currentInterval time.Duration
+	startTime       time.Time
+}
+
+// Clock is an interface that returns current time for BackOff.
+type Clock interface {
+	Now() time.Time
+}
+
+// Default values for ExponentialBackOff.
+const (
+	DefaultInitialInterval     = 500 * time.Millisecond
+	DefaultRandomizationFactor = 0.5
+	DefaultMultiplier          = 1.5
+	DefaultMaxInterval         = 60 * time.Second
+	DefaultMaxElapsedTime      = 15 * time.Minute
+)
+
+// NewExponentialBackOff creates an instance of ExponentialBackOff using default values.
+func NewExponentialBackOff() *ExponentialBackOff {
+	b := &ExponentialBackOff{
+		InitialInterval:     DefaultInitialInterval,
+		RandomizationFactor: DefaultRandomizationFactor,
+		Multiplier:          DefaultMultiplier,
+		MaxInterval:         DefaultMaxInterval,
+		MaxElapsedTime:      DefaultMaxElapsedTime,
+		Stop:                Stop,
+		Clock:               SystemClock,
+	}
+	b.Reset()
+	return b
+}
+
+type systemClock struct{}
+
+func (t systemClock) Now() time.Time {
+	return time.Now()
+}
+
+// SystemClock implements Clock interface that uses time.Now().
+var SystemClock = systemClock{}
+
+// Reset the interval back to the initial retry interval and restarts the timer.
+// Reset must be called before using b.
+func (b *ExponentialBackOff) Reset() {
+	b.currentInterval = b.InitialInterval
+	b.startTime = b.Clock.Now()
+}
+
+// NextBackOff calculates the next backoff interval using the formula:
+// 	Randomized interval = RetryInterval * (1 ± RandomizationFactor)
+func (b *ExponentialBackOff) NextBackOff() time.Duration {
+	// Make sure we have not gone over the maximum elapsed time.
+	elapsed := b.GetElapsedTime()
+	next := getRandomValueFromInterval(b.RandomizationFactor, rand.Float64(), b.currentInterval)
+	b.incrementCurrentInterval()
+	if b.MaxElapsedTime != 0 && elapsed+next > b.MaxElapsedTime {
+		return b.Stop
+	}
+	return next
+}
+
+// GetElapsedTime returns the elapsed time since an ExponentialBackOff instance
+// is created and is reset when Reset() is called.
+//
+// The elapsed time is computed using time.Now().UnixNano(). It is
+// safe to call even while the backoff policy is used by a running
+// ticker.
+func (b *ExponentialBackOff) GetElapsedTime() time.Duration {
+	return b.Clock.Now().Sub(b.startTime)
+}
+
+// Increments the current interval by multiplying it with the multiplier.
+func (b *ExponentialBackOff) incrementCurrentInterval() {
+	// Check for overflow, if overflow is detected set the current interval to the max interval.
+	if float64(b.currentInterval) >= float64(b.MaxInterval)/b.Multiplier {
+		b.currentInterval = b.MaxInterval
+	} else {
+		b.currentInterval = time.Duration(float64(b.currentInterval) * b.Multiplier)
+	}
+}
+
+// Returns a random value from the following interval:
+// 	[currentInterval - randomizationFactor * currentInterval, currentInterval + randomizationFactor * currentInterval].
+func getRandomValueFromInterval(randomizationFactor, random float64, currentInterval time.Duration) time.Duration {
+	var delta = randomizationFactor * float64(currentInterval)
+	var minInterval = float64(currentInterval) - delta
+	var maxInterval = float64(currentInterval) + delta
+
+	// Get a random value from the range [minInterval, maxInterval].
+	// The formula used below has a +1 because if the minInterval is 1 and the maxInterval is 3 then
+	// we want a 33% chance for selecting either 1, 2 or 3.
+	return time.Duration(minInterval + (random * (maxInterval - minInterval + 1)))
+}

vendor/github.com/cenkalti/backoff/v4/go.mod

+module github.com/cenkalti/backoff/v4
+
+go 1.13

vendor/github.com/cenkalti/backoff/v4/retry.go

+package backoff
+
+import (
+	"errors"
+	"time"
+)
+
+// An Operation is executing by Retry() or RetryNotify().
+// The operation will be retried using a backoff policy if it returns an error.
+type Operation func() error
+
+// Notify is a notify-on-error function. It receives an operation error and
+// backoff delay if the operation failed (with an error).
+//
+// NOTE that if the backoff policy stated to stop retrying,
+// the notify function isn't called.
+type Notify func(error, time.Duration)
+
+// Retry the operation o until it does not return error or BackOff stops.
+// o is guaranteed to be run at least once.
+//
+// If o returns a *PermanentError, the operation is not retried, and the
+// wrapped error is returned.
+//
+// Retry sleeps the goroutine for the duration returned by BackOff after a
+// failed operation returns.
+func Retry(o Operation, b BackOff) error {
+	return RetryNotify(o, b, nil)
+}
+
+// RetryNotify calls notify function with the error and wait duration
+// for each failed attempt before sleep.
+func RetryNotify(operation Operation, b BackOff, notify Notify) error {
+	return RetryNotifyWithTimer(operation, b, notify, nil)
+}
+
+// RetryNotifyWithTimer calls notify function with the error and wait duration using the given Timer
+// for each failed attempt before sleep.
+// A default timer that uses system timer is used when nil is passed.
+func RetryNotifyWithTimer(operation Operation, b BackOff, notify Notify, t Timer) error {
+	var err error
+	var next time.Duration
+	if t == nil {
+		t = &defaultTimer{}
+	}
+
+	defer func() {
+		t.Stop()
+	}()
+
+	ctx := getContext(b)
+
+	b.Reset()
+	for {
+		if err = operation(); err == nil {
+			return nil
+		}
+
+		var permanent *PermanentError
+		if errors.As(err, &permanent) {
+			return permanent.Err
+		}
+
+		if next = b.NextBackOff(); next == Stop {
+			return err
+		}
+
+		if notify != nil {
+			notify(err, next)
+		}
+
+		t.Start(next)
+
+		select {
+		case <-ctx.Done():
+			return ctx.Err()
+		case <-t.C():
+		}
+	}
+}
+
+// PermanentError signals that the operation should not be retried.
+type PermanentError struct {
+	Err error
+}
+
+func (e *PermanentError) Error() string {
+	return e.Err.Error()
+}
+
+func (e *PermanentError) Unwrap() error {
+	return e.Err
+}
+
+func (e *PermanentError) Is(target error) bool {
+	_, ok := target.(*PermanentError)
+	return ok
+}
+
+// Permanent wraps the given err in a *PermanentError.
+func Permanent(err error) error {
+	if err == nil {
+		return nil
+	}
+	return &PermanentError{