Implement rate limiting

[ChimeraCoder]

It should be straightforward to implement rate-limiting as https://github.com/ChimeraCoder/goangel does without changing the interface of the library.

[ChimeraCoder]

Technically, this involves rate-limiting based on "resource families": https://dev.twitter.com/docs/api/1.1/get/application/rate_limit_status

[bobrik]

I do graceful rate-limiting like this:

func TryUntilSucceeded(method func() (interface{}, error)) (result interface{}, err error) {
    for {
        result, err = method()

        if apiErr, ok := err.(*anaconda.ApiError); ok {
            limited, freed := apiErr.RateLimitCheck()
            if !limited {
                break
            } else {
                freed = freed.Add(5 * time.Second) // extra margin
                now := time.Now()
                fmt.Println("[rate limited] will wake up at", freed, "in", freed.Sub(now).Seconds(), "seconds")
                time.Sleep(freed.Sub(now))
                continue
            }
        } else {
            break
        }
    }

    return result, err
}

and usage looks like this:

users, err := TryUntilSucceeded(func() (interface {}, error) {
    return lookuper.Api.GetUsersLookupByIds(chunk, nil)
})

// users.([]anaconda.TwitterUser) to get profiles

I need #12 and ApiError to make this happen, but it works great. It also doesn't need time.Sleep() and can handle weird stuff at twitter side, unlike ChimeraCoder/goangel.

[ChimeraCoder]

Looks like we forgot to close this issue out before. Thanks @bobrik - the (optional) rate-limiting thats' now built-in is very similar to what you outline here.