var buf bytes.Buffer
	for _, k := range headers {
		buf.WriteString(k)
		buf.WriteByte(':')
		switch {
		case k == "host":
			buf.WriteString(req.URL.Host)
			fallthrough
		default:
			for idx, v := range headerMap[k] {
				if idx > 0 {
					buf.WriteByte(',')
				}
				buf.WriteString(v)
			}
			buf.WriteByte('\n')
		}
	}
	canonicalHeaders := buf.String()

	// Get signed headers.

	var s strings.Builder
	if x&xlFlagFreeVersion != 0 {
		s.WriteString("FreeVersion")
	}
	if x&xlFlagUsesDataDir != 0 {
		if s.Len() > 0 {
			s.WriteByte(',')
		}
		s.WriteString("UsesDD")
	}
	if x&xlFlagInlineData != 0 {
		if s.Len() > 0 {
			s.WriteByte(',')
		}
		s.WriteString("Inline")
	}
	return s.String()
}

func BenchmarkWriterEmpty(b *testing.B) {
	b.ReportAllocs()
	str := strings.Repeat("x", 1<<10)
	bs := []byte(str)
	for i := 0; i < b.N; i++ {
		bw := NewWriter(io.Discard)
		bw.Flush()
		bw.WriteByte('a')
		bw.Flush()
		bw.WriteRune('B')
		bw.Flush()
		bw.Write(bs)
		bw.Flush()
		bw.WriteString(str)
		bw.Flush()
	}
}

func BenchmarkWriterFlush(b *testing.B) {