mark responses as success in no redirect following mode.

[keijiyoshida]

Issue which this PR solves

Vegeta does not mark responses as success when -1 is set to the attack -redirects option. Bytes In, Bytes Out, Success and Status Codes of a report are zeros as below:

echo "GET http://xxxx.xxxx" | vegeta attack -redirects -1 -rate 1 -duration 10s | tee results.bin | vegeta report
Requests      [total, rate]            10, 1.11
Duration      [total, attack, wait]    9.003078071s, 8.999999898s, 3.078173ms
Latencies     [mean, 50, 95, 99, max]  12.427662ms, 3.246776ms, 3.823605ms, 3.823605ms, 96.816248ms
Bytes In      [total, mean]            0, 0.00
Bytes Out     [total, mean]            0, 0.00
Success       [ratio]                  0.00%
Status Codes  [code:count]             0:10
Error Set:

Changes in this PR

Have a.client.CheckRedirect return http.ErrUseLastResponse when -1 is set to the attack -redirects option. By doing this, Go's HTTP client does not follow redirects and returns the first HTTP response with its body unclosed. See https://golang.org/src/net/http/client.go?h=ErrUseLastResponse#L398 for the details.

[tsenart]

I'd rather have this code be the simpler version:

a.client.CheckRedirect = func(_ *http.Request, via []*http.Request) error {
    switch {
    case n == NoFollow:
        return http.ErrUseLastResponse
    case n < len(via):
        return fmt.Errorf("stopped after %d redirects", n)
    default:
        return nil
    }
}

[tsenart]

Can you please add a regression test that fails for the bug you're fixing?

[keijiyoshida]

@tsenart Thanks for your reviewing and sorry for the late response. I fixed the module and added a regression test. Thanks.