125 lines
3.2 KiB
Go
125 lines
3.2 KiB
Go
// Package temperrcatcher provides a TempErrCatcher object,
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// which implements simple error-retrying functionality.
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package temperrcatcher
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import (
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"time"
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)
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// InitialDelay governs how long to wait the first time.
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// This is defaulted to time.Millisecond, which makes sense
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// for network listener failures. You may want a much smaller
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// delay. You can configure this package wide, or in each
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// TempErrCatcher
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var InitialDelay = time.Millisecond
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// Temporary is an interface errors can implement to
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// ensure they are correctly classified by the default
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// TempErrCatcher classifier
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type Temporary interface {
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Temporary() bool
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}
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// ErrIsTemporary returns whether an error is Temporary(),
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// iff it implements the Temporary interface.
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func ErrIsTemporary(e error) bool {
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te, ok := e.(Temporary)
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return ok && te.Temporary()
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}
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// TempErrCatcher catches temporary errors for you. It then sleeps
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// for a bit before returning (you should then try again). This may
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// seem odd, but it's exactly what net/http does:
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// http://golang.org/src/net/http/server.go?s=51504:51550#L1728
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//
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// You can set a few options in TempErrCatcher. They all have defaults
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// so a zero TempErrCatcher is ready to be used:
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//
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// var c tec.TempErrCatcher
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// c.IsTemporary(tempErr)
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//
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type TempErrCatcher struct {
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IsTemp func(error) bool // the classifier to use. default: ErrIsTemporary
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Wait func(time.Duration) // the wait func to call. default: time.Sleep
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Max time.Duration // the maximum time to wait. default: time.Second
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Start time.Duration // the delay to start with. default: InitialDelay
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delay time.Duration
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last time.Time
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}
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func (tec *TempErrCatcher) init() {
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if tec.Max == 0 {
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tec.Max = time.Second
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}
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if tec.IsTemp == nil {
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tec.IsTemp = ErrIsTemporary
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}
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if tec.Wait == nil {
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tec.Wait = time.Sleep
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}
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if tec.Start == 0 {
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tec.Start = InitialDelay
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}
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}
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// IsTemporary checks whether an error is temporary. It will call
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// tec.Wait before returning, with a delay. The delay is also
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// doubled, so we do not constantly spin. This is the strategy
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// net.Listener uses.
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//
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// Note: you will want to call Reset() if you get a success,
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// so that the stored delay is brough back to 0.
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func (tec *TempErrCatcher) IsTemporary(e error) bool {
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tec.init()
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if tec.IsTemp(e) {
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now := time.Now()
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if now.Sub(tec.last) > (tec.delay * 5) {
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// this is a "new streak" of temp failures. reset.
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tec.Reset()
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}
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if tec.delay == 0 { // init case.
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tec.delay = tec.Start
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} else {
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tec.delay *= 2
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}
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if tec.delay > tec.Max {
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tec.delay = tec.Max
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}
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tec.Wait(tec.delay)
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tec.last = now
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return true
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}
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tec.Reset() // different failure. call reset
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return false
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}
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// Reset sets the internal delay counter to 0
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func (tec *TempErrCatcher) Reset() {
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tec.delay = 0
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}
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// ErrTemporary wraps any error and implements Temporary function.
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//
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// err := errors.New("beep boop")
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// var c tec.TempErrCatcher
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// c.IsTemporary(err) // false
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// c.IsTemporary(tec.ErrTemp{err}) // true
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//
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type ErrTemporary struct {
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Err error
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}
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func (e ErrTemporary) Temporary() bool {
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return true
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}
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func (e ErrTemporary) Error() string {
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return e.Err.Error()
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}
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func (e ErrTemporary) String() string {
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return e.Error()
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}
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