Replace

replace.go

// Replace reimplements bytes.Replace in a way that can reuse the buffer
func Replace(s, old, new []byte, n int, buf *bytes.Buffer) error {
	m := 0

	if n != 0 {
		// Compute number of replacements.
		m = bytes.Count(s, old)
	}

	if buf == nil {
		buf = &bytes.Buffer{}
	}

	buf.Reset()

	if m == 0 {
		// Just return a copy.
		_, err := buf.Write(s)
		return err
	}

	if n < 0 || m < n {
		n = m
	}

	// Apply replacements to buffer.
	buf.Grow(len(s) + n*(len(new)-len(old)))

	start := 0
	for i := 0; i < n; i++ {
		j := start

		if len(old) == 0 {
			if i > 0 {
				_, wid := utf8.DecodeRune(s[start:])
				j += wid
			}
		} else {
			j += bytes.Index(s[start:], old)
		}

		if _, err := buf.Write(s[start:j]); err != nil {
			return err
		}

		if _, err := buf.Write(new); err != nil {
			return err
		}

		start = j + len(old)
	}

	_, err := buf.Write(s[start:])
	return err
}