errOnce.Do(func() {
							retError = err.Error()
						})
					}
					downloadsCancel()
					return
				}
				fbr := firstByteRecorder{
					r: r,
				}
				n, err := xioutil.Copy(xioutil.Discard, &fbr)
				r.Close()
				if err == nil {
					response := time.Since(t)
					ttfb := time.Since(*fbr.t)
					// Only capture success criteria - do not
					// have to capture failed reads, truncated