if ifModifiedSinceHeader != "" {
		if givenTime, err := amztime.ParseHeader(ifModifiedSinceHeader); err == nil {
			r.IfModifiedSince = &givenTime
		}
	}
	ifUnmodifiedSinceHeader := header.Get(xhttp.IfUnmodifiedSince)
	if ifUnmodifiedSinceHeader != "" {
		if givenTime, err := amztime.ParseHeader(ifUnmodifiedSinceHeader); err == nil {
			r.IfUnModifiedSince = &givenTime
		}
	}

	return false
}

// returns true if object was modified after givenTime.
func ifModifiedSince(objTime time.Time, givenTime time.Time) bool {
	// The Date-Modified header truncates sub-second precision, so
	// use mtime < t+1s instead of mtime <= t to check for unmodified.
	return objTime.After(givenTime.Add(1 * time.Second))
}