Fix bad format error caused by negative duration

[wuYin]

Motivation

Fix issue #48

• describe

  bad format error occurred if delay or ttr is less than -1s.

• reproduce

  c, _ := beanstalk.Dial("tcp", "127.0.0.1:11300")
  _, err := c.Put([]byte("abc"), 0, -1*time.Second, 0)
  fmt.Println(err) // put: bad command format

• cause
  '-' (-1s) is illegal char foruint32, see prot.c#L1048

Modification

dur.String() replaced by dur2sec(time.Duration) string utility function.

[kr]

Hi! Thanks for doing the work to write this patch, but since the server doesn’t support negative durations, I would argue it’s good for this situation to return an error. For example, maybe an application bug has resulted in an unintended negative duration; then it’ll be easier to find that bug if an error shows up.

However, it would certainly help a lot more if a more specific & descriptive error could be returned instead of the general bad format error. It would also be nice to avoid an unnecessary round trip to the server in that case.

How does that sound to you?

[wuYin]

Thanks for review.
Make sense to me, this patch actually doesn't solve the essential problem.
User should find and fix the problem by himself based on the error returned.

[wuYin]

@kr
Sorry to repoen this PR.
In this bad format case, maybe parameter delaySec uint32 is better than delay time.Duration ?
It's semantic is easier to understand, and with type checking.
The reason for using uint32 is that server read duration actually read uint32, see prot.c#L1073

[kr]

Using a uint32 would remove the possibility of negative values, but it would introduce ambiguity about the units (seconds, milliseconds, etc) and it would be a breaking change. I think it’s better to stick with time.Duration, since that’s the standard way to represent a duration in Go.

I think I’d prefer to see a check at the top of method Conn.cmd along these lines:

for _, a := range args {
    if d, _ := a.(time.Duration); d < 0 {
        return req{}, fmt.Errorf("duration must be non-negative, got %v", d)
    }
}

This would still eliminate the need for the internal type dur, like you’ve already done in this change.

[wuYin]

Thanks for review and suggestions, good idea.
Now reserved extensibility for negative duration and without breaking type change, only add type checking for dur before using it

[kr]

Awesome, thanks for your patience and perseverance!