118 lines
3.3 KiB
Go
118 lines
3.3 KiB
Go
package retry
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import (
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"context"
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"fmt"
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"log"
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"time"
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)
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// Config represents a retry config
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type Config struct {
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// The operation will be retried until StartTimeout has elapsed. 0 means
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// forever.
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StartTimeout time.Duration
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// RetryDelay gives the time elapsed after a failure and before we try
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// again. Returns 2s by default.
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RetryDelay func() time.Duration
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// Max number of retries, 0 means infinite
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Tries int
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// ShouldRetry tells whether error should be retried. Nil defaults to always
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// true.
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ShouldRetry func(error) bool
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}
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type RetryExhaustedError struct {
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Err error
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}
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func (err *RetryExhaustedError) Error() string {
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if err == nil || err.Err == nil {
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return "<nil>"
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}
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return fmt.Sprintf("retry count exhausted. Last err: %s", err.Err)
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}
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// Run will repeatedly retry the proivided fn within the constraints set in the
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// retry Config. It will retry until one of the following conditions is met:
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// - The provided context is cancelled.
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// - The Config.StartTimeout time has passed.
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// - The function returns without an error.
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// - The maximum number of tries, Config.Tries is exceeded.
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// - The function returns with an error that does not satisfy conditions
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// set in the Config.ShouldRetry function.
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// If the given function (fn) does not return an error, then Run will return
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// nil. Otherwise, Run will return a relevant error.
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func (cfg Config) Run(ctx context.Context, fn func(context.Context) error) error {
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retryDelay := func() time.Duration { return 2 * time.Second }
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if cfg.RetryDelay != nil {
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retryDelay = cfg.RetryDelay
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}
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shouldRetry := func(error) bool { return true }
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if cfg.ShouldRetry != nil {
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shouldRetry = cfg.ShouldRetry
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}
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var startTimeout <-chan time.Time // nil chans never unlock !
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if cfg.StartTimeout != 0 {
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startTimeout = time.After(cfg.StartTimeout)
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}
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var err error
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for try := 0; ; try++ {
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if cfg.Tries != 0 && try == cfg.Tries {
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return &RetryExhaustedError{err}
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}
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if err = fn(ctx); err == nil {
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return nil
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}
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if !shouldRetry(err) {
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return err
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}
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log.Print(fmt.Errorf("Retryable error: %s", err))
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select {
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case <-ctx.Done():
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return err
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case <-startTimeout:
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return err
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default:
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time.Sleep(retryDelay())
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}
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}
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}
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// Backoff is a self contained backoff time calculator. This struct should be
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// passed around as a copy as it changes its own fields upon any Backoff call.
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// Backoff is not thread safe. For now only a Linear backoff call is
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// implemented and the Exponential call will be implemented when needed.
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type Backoff struct {
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// Initial time to wait. A Backoff call will change this value.
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InitialBackoff time.Duration
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// Maximum time returned.
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MaxBackoff time.Duration
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// For a Linear backoff, InitialBackoff will be multiplied by Multiplier
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// after each call.
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Multiplier float64
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}
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// Linear Backoff returns a linearly increasing Duration.
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// n = n * Multiplier.
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// the first value of n is InitialBackoff. n is maxed by MaxBackoff.
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func (lb *Backoff) Linear() time.Duration {
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wait := lb.InitialBackoff
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lb.InitialBackoff = time.Duration(lb.Multiplier * float64(lb.InitialBackoff))
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if lb.MaxBackoff != 0 && lb.InitialBackoff > lb.MaxBackoff {
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lb.InitialBackoff = lb.MaxBackoff
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}
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return wait
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}
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// Exponential backoff panics: not implemented, yet.
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func (lb *Backoff) Exponential() time.Duration {
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panic("not implemented, yet")
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}
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