Fix duration is zero

[daixiang0]

When MaxBackoff not set, after one loop, duration is always bigger than
it, so duration set as zero, then following panic occur:

panic: invalid argument to Int63n

goroutine 169 [running]:
math/rand.(*Rand).Int63n(0xc0000cc150, 0x0, 0xc000719b58)
	/usr/lib/golang/src/math/rand/rand.go:111 +0x11e
math/rand.Int63n(...)
	/usr/lib/golang/src/math/rand/rand.go:319

Signed-off-by: Xiang Dai [email protected]

[bboreham]

How did you get into this situation?

Backoff is meant to be used with non-zero parameters, so that it waits an increasing amount of time. I can't see what a zero-time delay would be good for.

[daixiang0]

The key is to solve the panic, since i want even without set MaxBackoff, backoff could work without panic.

[bboreham]

I think it would be simpler to just put a check if b.duration == 0 {return} near the top of Wait(), maybe with a comment that this covers the case where the user has configured a zero min or max time.

It's probably also unexpected that a zero minimum time with non-zero max time will result in zero waits.
See also #792

[daixiang0]

Do you mean min/max time is required field so no need to change here but check at caller?

[bboreham]

This has been overtaken by #1599