golang retry func() error

retry.go

package retry

import (
	"context"
	"fmt"
	"time"

	"github.com/go-logr/logr"
)

// retry retries a `func() error` up to `attempts` times, sleeping for the duration `sleep`*2^`attempt`.
// It will swallow all errors except the last one.
func retry(ctx context.Context, log logr.Logger, attempts int, sleep time.Duration, f func() error) error {
	log = log.
		WithName("retry").
		WithValues("attempts", attempts, "sleep", sleep)

	var err error

	i := 0
	for {
		select {
		case <-ctx.Done():
			return ctx.Err()
		default:
			// bail if too many retry attempts have already been made
			if i >= attempts {
				return fmt.Errorf("gave up after %d attempts. last error: %w", attempts, err)
			}
			// sleep if we're not on the first iteration because that means that a previous iteration errored
			if i > 0 {
				log.Error(err, "function errored", "i", i)
				time.Sleep(sleep)
				sleep *= 2
			}
			// try to run `f()`
			if err = f(); err == nil {
				return nil
			}
			i++
		}
	}
}

retry_test.go

package retry

import (
	"context"
	"fmt"
	"testing"
	"time"

	"github.com/go-logr/logr"
	"github.com/stretchr/testify/require"
)

func failingFuncFactory(failures int, err error) func() error {
	i := 0

	return func() error {
		if i < failures {
			i++
			return err
		}
		return nil
	}
}

var errNever = fmt.Errorf("never gonna give you up")

func TestRetry(t *testing.T) {
	t.Parallel()

	log := logr.New(nil)

	{
		ctx, cancel := context.WithTimeout(context.Background(), time.Second)
		defer cancel()
		err := retry(ctx, log, 1, time.Millisecond, failingFuncFactory(0, errNever))
		require.Nil(t, err)
	}

	{
		ctx, cancel := context.WithTimeout(context.Background(), time.Second)
		defer cancel()
		err := retry(ctx, log, 2, time.Millisecond, failingFuncFactory(1, errNever))
		require.Nil(t, err)
	}

	{
		ctx, cancel := context.WithTimeout(context.Background(), time.Second)
		defer cancel()
		err := retry(ctx, log, 2, time.Millisecond, failingFuncFactory(2, errNever))
		require.ErrorIs(t, err, errNever)
	}

	{
		ctx, cancel := context.WithTimeout(context.Background(), time.Second)
		defer cancel()
		err := retry(ctx, log, 5, time.Millisecond, failingFuncFactory(5, errNever))
		require.ErrorIs(t, err, errNever)
	}
}