Optimize frame encodeValue unencodeValue, replace with more efficient version

[hanjm]

Using strings.Replace multi times in "encodeValue" and "unencodeValue" function is low efficience, strings.NewReplacer is the more efficient version, here is the benchmark result.

/*
$ go test -check.v -check.b -check.bmem
PASS: encode_test.go:32: EncodeSuite.BenchmarkEncodeValue       10000000               223 ns/op             112 B/op          1 allocs/op
PASS: encode_test.go:48: EncodeSuite.BenchmarkEncodeValueOld     5000000               504 ns/op             480 B/op          9 allocs/op
PASS: encode_test.go:40: EncodeSuite.BenchmarkUnencodeValue      5000000               357 ns/op             208 B/op          4 allocs/op
PASS: encode_test.go:56: EncodeSuite.BenchmarkUnencodeValueOld   5000000               556 ns/op             448 B/op          9 allocs/op
OK: 4 passed
PASS
*/
func (s *EncodeSuite) BenchmarkEncodeValue(c *C) {
	val := "Contains\r\nNewLine and : colon and \\ backslash"
	c.ResetTimer()
	for i := 0; i < c.N; i++ {
		encodeValue(val)
	}
}

func (s *EncodeSuite) BenchmarkUnencodeValue(c *C) {
	val := []byte(`Contains\r\nNewLine and \c colon and \\ backslash`)
	c.ResetTimer()
	for i := 0; i < c.N; i++ {
		unencodeValue(val)
	}
}

func (s *EncodeSuite) BenchmarkEncodeValueOld(c *C) {
	val := "Contains\r\nNewLine and : colon and \\ backslash"
	c.ResetTimer()
	for i := 0; i < c.N; i++ {
		encodeValueOld(val)
	}
}

func (s *EncodeSuite) BenchmarkUnencodeValueOld(c *C) {
	val := []byte(`Contains\r\nNewLine and \c colon and \\ backslash`)
	c.ResetTimer()
	for i := 0; i < c.N; i++ {
		unencodeValueOld(val)
	}
}

func encodeValueOld(s string) []byte {
	s = strings.Replace(s, "\\", "\\\\", -1)
	s = strings.Replace(s, "\r", "\\r", -1)
	s = strings.Replace(s, "\n", "\\n", -1)
	s = strings.Replace(s, ":", "\\c", -1)
	return []byte(s)
}

func unencodeValueOld(b []byte) (string, error) {
	s := string(b)
	s = strings.Replace(s, "\\r", "\r", -1)
	s = strings.Replace(s, "\\n", "\n", -1)
	s = strings.Replace(s, "\\c", ":", -1)
	s = strings.Replace(s, "\\\\", "\\", -1)
	return s, nil
}

[hanjm]

you can see the std lib code, strings/replace.go https://golang.org/src/strings/replace.go#L315:

func (r *genericReplacer) Replace(s string) string {
	buf := make(appendSliceWriter, 0, len(s))
	r.WriteString(&buf, s)
	return string(buf)
}

using []byte(replacerForEncodeValue.Replace(s)) make unnecessary bytes to string and strings to bytes transformation.