Port ANSI escape code parser to Go

tools/utils/shlex/ansi_c_escapes.go

@@ -0,0 +1,148 @@
+// License: GPLv3 Copyright: 2022, Kovid Goyal, <kovid at kovidgoyal.net>
+
+package shlex
+
+import (
+	"fmt"
+	"strconv"
+	"strings"
+)
+
+var _ = fmt.Print
+
+type state int
+
+const (
+	normal state = iota
+	control_char
+	backslash
+	hex_digit
+	oct_digit
+)
+
+type ansi_c struct {
+	state                        state
+	max_num_of_digits, digit_idx int
+	digits                       [16]rune
+	output                       strings.Builder
+}
+
+func is_hex_char(ch rune) bool {
+	return ('0' <= ch && ch <= '9') || ('a' <= ch && ch <= 'f') || ('A' <= ch && ch <= 'F')
+}
+
+func is_oct_char(ch rune) bool {
+	return '0' <= ch && ch <= '7'
+}
+
+func (self *ansi_c) write_digits(base int) {
+	if self.digit_idx > 0 {
+		text := string(self.digits[:self.digit_idx])
+		val, err := strconv.ParseUint(text, base, 32)
+		if err == nil {
+			self.output.WriteRune(rune(val))
+		}
+	}
+	self.digit_idx = 0
+	self.state = normal
+}
+
+func (self *ansi_c) parse(ch rune) {
+	switch self.state {
+	case normal:
+		if ch == '\\' {
+			self.state = backslash
+		} else {
+			self.output.WriteRune(ch)
+		}
+	case control_char:
+		self.output.WriteRune(ch & 0x1f)
+		self.state = normal
+	case hex_digit:
+		if self.digit_idx < self.max_num_of_digits && is_hex_char(ch) {
+			self.digits[self.digit_idx] = ch
+			self.digit_idx++
+		} else {
+			self.write_digits(16)
+			self.parse(ch)
+		}
+	case oct_digit:
+		if self.digit_idx < self.max_num_of_digits && is_oct_char(ch) {
+			self.digits[self.digit_idx] = ch
+			self.digit_idx++
+		} else {
+			self.write_digits(8)
+			self.parse(ch)
+		}
+	case backslash:
+		self.state = normal
+		switch ch {
+		default:
+			self.output.WriteRune('\\')
+			self.output.WriteRune(ch)
+		case 'a':
+			self.output.WriteRune(7)
+		case 'b':
+			self.output.WriteRune(8)
+		case 'c':
+			self.state = control_char
+		case 'e', 'E':
+			self.output.WriteRune(27)
+		case 'f':
+			self.output.WriteRune(12)
+		case 'n':
+			self.output.WriteRune(10)
+		case 'r':
+			self.output.WriteRune(13)
+		case 't':
+			self.output.WriteRune(9)
+		case 'v':
+			self.output.WriteRune(11)
+		case 'x':
+			self.max_num_of_digits, self.digit_idx, self.state = 2, 0, hex_digit
+		case 'u':
+			self.max_num_of_digits, self.digit_idx, self.state = 4, 0, hex_digit
+		case 'U':
+			self.max_num_of_digits, self.digit_idx, self.state = 8, 0, hex_digit
+		case '0', '1', '2', '3', '4', '5', '6', '7':
+			self.max_num_of_digits, self.digit_idx, self.state = 3, 1, oct_digit
+			self.digits[0] = ch
+		case '\\':
+			self.output.WriteRune('\\')
+		case '?':
+			self.output.WriteRune('?')
+		case '"':
+			self.output.WriteRune('"')
+		case '\'':
+			self.output.WriteRune('\'')
+
+		}
+	}
+}
+
+func (self *ansi_c) finish() string {
+	switch self.state {
+	case hex_digit:
+		self.write_digits(16)
+	case oct_digit:
+		self.write_digits(8)
+	case backslash:
+		self.output.WriteRune('\\')
+	case control_char:
+		self.output.WriteString("\\c")
+	}
+	self.state = normal
+	self.digit_idx = 0
+	s := self.output.String()
+	self.output.Reset()
+	return s
+}
+
+func ExpandANSICEscapes(src string) string {
+	p := ansi_c{}
+	p.output.Grow(len(src))
+	for _, ch := range src {
+		p.parse(ch)
+	}
+	return p.finish()
+}