[perf] Avoid allocating rune array for ascii string

In the best case (all ascii), this reduces the memory footprint by 60%
and the response time by 15% to 20%. In the worst case (every line has
non-ascii characters), 3 to 4% overhead is observed.

src/util/chars.go

@@ -0,0 +1,113 @@
+package util
+
+import (
+	"unicode/utf8"
+)
+
+type Chars struct {
+	runes []rune
+	bytes []byte
+}
+
+// ToChars converts byte array into rune array
+func ToChars(bytea []byte) Chars {
+	var runes []rune
+	ascii := true
+	numBytes := len(bytea)
+	for i := 0; i < numBytes; {
+		if bytea[i] < utf8.RuneSelf {
+			if !ascii {
+				runes = append(runes, rune(bytea[i]))
+			}
+			i++
+		} else {
+			if ascii {
+				ascii = false
+				runes = make([]rune, i, numBytes)
+				for j := 0; j < i; j++ {
+					runes[j] = rune(bytea[j])
+				}
+			}
+			r, sz := utf8.DecodeRune(bytea[i:])
+			i += sz
+			runes = append(runes, r)
+		}
+	}
+	if ascii {
+		return Chars{bytes: bytea}
+	}
+	return Chars{runes: runes}
+}
+
+func RunesToChars(runes []rune) Chars {
+	return Chars{runes: runes}
+}
+
+func (chars *Chars) Get(i int) rune {
+	if chars.runes != nil {
+		return chars.runes[i]
+	}
+	return rune(chars.bytes[i])
+}
+
+func (chars *Chars) Length() int {
+	if chars.runes != nil {
+		return len(chars.runes)
+	}
+	return len(chars.bytes)
+}
+
+// TrimLength returns the length after trimming leading and trailing whitespaces
+func (chars *Chars) TrimLength() int {
+	var i int
+	len := chars.Length()
+	for i = len - 1; i >= 0; i-- {
+		char := chars.Get(i)
+		if char != ' ' && char != '\t' {
+			break
+		}
+	}
+	// Completely empty
+	if i < 0 {
+		return 0
+	}
+
+	var j int
+	for j = 0; j < len; j++ {
+		char := chars.Get(j)
+		if char != ' ' && char != '\t' {
+			break
+		}
+	}
+	return i - j + 1
+}
+
+func (chars *Chars) TrailingWhitespaces() int {
+	whitespaces := 0
+	for i := chars.Length() - 1; i >= 0; i-- {
+		char := chars.Get(i)
+		if char != ' ' && char != '\t' {
+			break
+		}
+		whitespaces++
+	}
+	return whitespaces
+}
+
+func (chars *Chars) ToString() string {
+	if chars.runes != nil {
+		return string(chars.runes)
+	}
+	return string(chars.bytes)
+}
+
+func (chars *Chars) ToRunes() []rune {
+	if chars.runes != nil {
+		return chars.runes
+	}
+	runes := make([]rune, len(chars.bytes))
+	for idx, b := range chars.bytes {
+		runes[idx] = rune(b)
+	}
+	return runes
+}