1 files changed, 455 insertions, 0 deletions
diff --git a/src/strconv/quote.go b/src/strconv/quote.go
new file mode 100644
index 000000000..53d51b5a4
--- /dev/null
+++ b/src/strconv/quote.go
@@ -0,0 +1,455 @@
+// Copyright 2009 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+//go:generate go run makeisprint.go -output isprint.go
+
+package strconv
+
+import (
+	"unicode/utf8"
+)
+
+const lowerhex = "0123456789abcdef"
+
+func quoteWith(s string, quote byte, ASCIIonly bool) string {
+	var runeTmp [utf8.UTFMax]byte
+	buf := make([]byte, 0, 3*len(s)/2) // Try to avoid more allocations.
+	buf = append(buf, quote)
+	for width := 0; len(s) > 0; s = s[width:] {
+		r := rune(s[0])
+		width = 1
+		if r >= utf8.RuneSelf {
+			r, width = utf8.DecodeRuneInString(s)
+		}
+		if width == 1 && r == utf8.RuneError {
+			buf = append(buf, `\x`...)
+			buf = append(buf, lowerhex[s[0]>>4])
+			buf = append(buf, lowerhex[s[0]&0xF])
+			continue
+		}
+		if r == rune(quote) || r == '\\' { // always backslashed
+			buf = append(buf, '\\')
+			buf = append(buf, byte(r))
+			continue
+		}
+		if ASCIIonly {
+			if r < utf8.RuneSelf && IsPrint(r) {
+				buf = append(buf, byte(r))
+				continue
+			}
+		} else if IsPrint(r) {
+			n := utf8.EncodeRune(runeTmp[:], r)
+			buf = append(buf, runeTmp[:n]...)
+			continue
+		}
+		switch r {
+		case '\a':
+			buf = append(buf, `\a`...)
+		case '\b':
+			buf = append(buf, `\b`...)
+		case '\f':
+			buf = append(buf, `\f`...)
+		case '\n':
+			buf = append(buf, `\n`...)
+		case '\r':
+			buf = append(buf, `\r`...)
+		case '\t':
+			buf = append(buf, `\t`...)
+		case '\v':
+			buf = append(buf, `\v`...)
+		default:
+			switch {
+			case r < ' ':
+				buf = append(buf, `\x`...)
+				buf = append(buf, lowerhex[s[0]>>4])
+				buf = append(buf, lowerhex[s[0]&0xF])
+			case r > utf8.MaxRune:
+				r = 0xFFFD
+				fallthrough
+			case r < 0x10000:
+				buf = append(buf, `\u`...)
+				for s := 12; s >= 0; s -= 4 {
+					buf = append(buf, lowerhex[r>>uint(s)&0xF])
+				}
+			default:
+				buf = append(buf, `\U`...)
+				for s := 28; s >= 0; s -= 4 {
+					buf = append(buf, lowerhex[r>>uint(s)&0xF])
+				}
+			}
+		}
+	}
+	buf = append(buf, quote)
+	return string(buf)
+
+}
+
+// Quote returns a double-quoted Go string literal representing s.  The
+// returned string uses Go escape sequences (\t, \n, \xFF, \u0100) for
+// control characters and non-printable characters as defined by
+// IsPrint.
+func Quote(s string) string {
+	return quoteWith(s, '"', false)
+}
+
+// AppendQuote appends a double-quoted Go string literal representing s,
+// as generated by Quote, to dst and returns the extended buffer.
+func AppendQuote(dst []byte, s string) []byte {
+	return append(dst, Quote(s)...)
+}
+
+// QuoteToASCII returns a double-quoted Go string literal representing s.
+// The returned string uses Go escape sequences (\t, \n, \xFF, \u0100) for
+// non-ASCII characters and non-printable characters as defined by IsPrint.
+func QuoteToASCII(s string) string {
+	return quoteWith(s, '"', true)
+}
+
+// AppendQuoteToASCII appends a double-quoted Go string literal representing s,
+// as generated by QuoteToASCII, to dst and returns the extended buffer.
+func AppendQuoteToASCII(dst []byte, s string) []byte {
+	return append(dst, QuoteToASCII(s)...)
+}
+
+// QuoteRune returns a single-quoted Go character literal representing the
+// rune.  The returned string uses Go escape sequences (\t, \n, \xFF, \u0100)
+// for control characters and non-printable characters as defined by IsPrint.
+func QuoteRune(r rune) string {
+	// TODO: avoid the allocation here.
+	return quoteWith(string(r), '\'', false)
+}
+
+// AppendQuoteRune appends a single-quoted Go character literal representing the rune,
+// as generated by QuoteRune, to dst and returns the extended buffer.
+func AppendQuoteRune(dst []byte, r rune) []byte {
+	return append(dst, QuoteRune(r)...)
+}
+
+// QuoteRuneToASCII returns a single-quoted Go character literal representing
+// the rune.  The returned string uses Go escape sequences (\t, \n, \xFF,
+// \u0100) for non-ASCII characters and non-printable characters as defined
+// by IsPrint.
+func QuoteRuneToASCII(r rune) string {
+	// TODO: avoid the allocation here.
+	return quoteWith(string(r), '\'', true)
+}
+
+// AppendQuoteRuneToASCII appends a single-quoted Go character literal representing the rune,
+// as generated by QuoteRuneToASCII, to dst and returns the extended buffer.
+func AppendQuoteRuneToASCII(dst []byte, r rune) []byte {
+	return append(dst, QuoteRuneToASCII(r)...)
+}
+
+// CanBackquote reports whether the string s can be represented
+// unchanged as a single-line backquoted string without control
+// characters other than tab.
+func CanBackquote(s string) bool {
+	for len(s) > 0 {
+		r, wid := utf8.DecodeRuneInString(s)
+		s = s[wid:]
+		if wid > 1 {
+			if r == '\ufeff' {
+				return false // BOMs are invisible and should not be quoted.
+			}
+			continue // All other multibyte runes are correctly encoded and assumed printable.
+		}
+		if r == utf8.RuneError {
+			return false
+		}
+		if (r < ' ' && r != '\t') || r == '`' || r == '\u007F' {
+			return false
+		}
+	}
+	return true
+}
+
+func unhex(b byte) (v rune, ok bool) {
+	c := rune(b)
+	switch {
+	case '0' <= c && c <= '9':
+		return c - '0', true
+	case 'a' <= c && c <= 'f':
+		return c - 'a' + 10, true
+	case 'A' <= c && c <= 'F':
+		return c - 'A' + 10, true
+	}
+	return
+}
+
+// UnquoteChar decodes the first character or byte in the escaped string
+// or character literal represented by the string s.
+// It returns four values:
+//
+//	1) value, the decoded Unicode code point or byte value;
+//	2) multibyte, a boolean indicating whether the decoded character requires a multibyte UTF-8 representation;
+//	3) tail, the remainder of the string after the character; and
+//	4) an error that will be nil if the character is syntactically valid.
+//
+// The second argument, quote, specifies the type of literal being parsed
+// and therefore which escaped quote character is permitted.
+// If set to a single quote, it permits the sequence \' and disallows unescaped '.
+// If set to a double quote, it permits \" and disallows unescaped ".
+// If set to zero, it does not permit either escape and allows both quote characters to appear unescaped.
+func UnquoteChar(s string, quote byte) (value rune, multibyte bool, tail string, err error) {
+	// easy cases
+	switch c := s[0]; {
+	case c == quote && (quote == '\'' || quote == '"'):
+		err = ErrSyntax
+		return
+	case c >= utf8.RuneSelf:
+		r, size := utf8.DecodeRuneInString(s)
+		return r, true, s[size:], nil
+	case c != '\\':
+		return rune(s[0]), false, s[1:], nil
+	}
+
+	// hard case: c is backslash
+	if len(s) <= 1 {
+		err = ErrSyntax
+		return
+	}
+	c := s[1]
+	s = s[2:]
+
+	switch c {
+	case 'a':
+		value = '\a'
+	case 'b':
+		value = '\b'
+	case 'f':
+		value = '\f'
+	case 'n':
+		value = '\n'
+	case 'r':
+		value = '\r'
+	case 't':
+		value = '\t'
+	case 'v':
+		value = '\v'
+	case 'x', 'u', 'U':
+		n := 0
+		switch c {
+		case 'x':
+			n = 2
+		case 'u':
+			n = 4
+		case 'U':
+			n = 8
+		}
+		var v rune
+		if len(s) < n {
+			err = ErrSyntax
+			return
+		}
+		for j := 0; j < n; j++ {
+			x, ok := unhex(s[j])
+			if !ok {
+				err = ErrSyntax
+				return
+			}
+			v = v<<4 | x
+		}
+		s = s[n:]
+		if c == 'x' {
+			// single-byte string, possibly not UTF-8
+			value = v
+			break
+		}
+		if v > utf8.MaxRune {
+			err = ErrSyntax
+			return
+		}
+		value = v
+		multibyte = true
+	case '0', '1', '2', '3', '4', '5', '6', '7':
+		v := rune(c) - '0'
+		if len(s) < 2 {
+			err = ErrSyntax
+			return
+		}
+		for j := 0; j < 2; j++ { // one digit already; two more
+			x := rune(s[j]) - '0'
+			if x < 0 || x > 7 {
+				err = ErrSyntax
+				return
+			}
+			v = (v << 3) | x
+		}
+		s = s[2:]
+		if v > 255 {
+			err = ErrSyntax
+			return
+		}
+		value = v
+	case '\\':
+		value = '\\'
+	case '\'', '"':
+		if c != quote {
+			err = ErrSyntax
+			return
+		}
+		value = rune(c)
+	default:
+		err = ErrSyntax
+		return
+	}
+	tail = s
+	return
+}
+
+// Unquote interprets s as a single-quoted, double-quoted,
+// or backquoted Go string literal, returning the string value
+// that s quotes.  (If s is single-quoted, it would be a Go
+// character literal; Unquote returns the corresponding
+// one-character string.)
+func Unquote(s string) (t string, err error) {
+	n := len(s)
+	if n < 2 {
+		return "", ErrSyntax
+	}
+	quote := s[0]
+	if quote != s[n-1] {
+		return "", ErrSyntax
+	}
+	s = s[1 : n-1]
+
+	if quote == '`' {
+		if contains(s, '`') {
+			return "", ErrSyntax
+		}
+		return s, nil
+	}
+	if quote != '"' && quote != '\'' {
+		return "", ErrSyntax
+	}
+	if contains(s, '\n') {
+		return "", ErrSyntax
+	}
+
+	// Is it trivial?  Avoid allocation.
+	if !contains(s, '\\') && !contains(s, quote) {
+		switch quote {
+		case '"':
+			return s, nil
+		case '\'':
+			r, size := utf8.DecodeRuneInString(s)
+			if size == len(s) && (r != utf8.RuneError || size != 1) {
+				return s, nil
+			}
+		}
+	}
+
+	var runeTmp [utf8.UTFMax]byte
+	buf := make([]byte, 0, 3*len(s)/2) // Try to avoid more allocations.
+	for len(s) > 0 {
+		c, multibyte, ss, err := UnquoteChar(s, quote)
+		if err != nil {
+			return "", err
+		}
+		s = ss
+		if c < utf8.RuneSelf || !multibyte {
+			buf = append(buf, byte(c))
+		} else {
+			n := utf8.EncodeRune(runeTmp[:], c)
+			buf = append(buf, runeTmp[:n]...)
+		}
+		if quote == '\'' && len(s) != 0 {
+			// single-quoted must be single character
+			return "", ErrSyntax
+		}
+	}
+	return string(buf), nil
+}
+
+// contains reports whether the string contains the byte c.
+func contains(s string, c byte) bool {
+	for i := 0; i < len(s); i++ {
+		if s[i] == c {
+			return true
+		}
+	}
+	return false
+}
+
+// bsearch16 returns the smallest i such that a[i] >= x.
+// If there is no such i, bsearch16 returns len(a).
+func bsearch16(a []uint16, x uint16) int {
+	i, j := 0, len(a)
+	for i < j {
+		h := i + (j-i)/2
+		if a[h] < x {
+			i = h + 1
+		} else {
+			j = h
+		}
+	}
+	return i
+}
+
+// bsearch32 returns the smallest i such that a[i] >= x.
+// If there is no such i, bsearch32 returns len(a).
+func bsearch32(a []uint32, x uint32) int {
+	i, j := 0, len(a)
+	for i < j {
+		h := i + (j-i)/2
+		if a[h] < x {
+			i = h + 1
+		} else {
+			j = h
+		}
+	}
+	return i
+}
+
+// TODO: IsPrint is a local implementation of unicode.IsPrint, verified by the tests
+// to give the same answer. It allows this package not to depend on unicode,
+// and therefore not pull in all the Unicode tables. If the linker were better
+// at tossing unused tables, we could get rid of this implementation.
+// That would be nice.
+
+// IsPrint reports whether the rune is defined as printable by Go, with
+// the same definition as unicode.IsPrint: letters, numbers, punctuation,
+// symbols and ASCII space.
+func IsPrint(r rune) bool {
+	// Fast check for Latin-1
+	if r <= 0xFF {
+		if 0x20 <= r && r <= 0x7E {
+			// All the ASCII is printable from space through DEL-1.
+			return true
+		}
+		if 0xA1 <= r && r <= 0xFF {
+			// Similarly for ¡ through ÿ...
+			return r != 0xAD // ...except for the bizarre soft hyphen.
+		}
+		return false
+	}
+
+	// Same algorithm, either on uint16 or uint32 value.
+	// First, find first i such that isPrint[i] >= x.
+	// This is the index of either the start or end of a pair that might span x.
+	// The start is even (isPrint[i&^1]) and the end is odd (isPrint[i|1]).
+	// If we find x in a range, make sure x is not in isNotPrint list.
+
+	if 0 <= r && r < 1<<16 {
+		rr, isPrint, isNotPrint := uint16(r), isPrint16, isNotPrint16
+		i := bsearch16(isPrint, rr)
+		if i >= len(isPrint) || rr < isPrint[i&^1] || isPrint[i|1] < rr {
+			return false
+		}
+		j := bsearch16(isNotPrint, rr)
+		return j >= len(isNotPrint) || isNotPrint[j] != rr
+	}
+
+	rr, isPrint, isNotPrint := uint32(r), isPrint32, isNotPrint32
+	i := bsearch32(isPrint, rr)
+	if i >= len(isPrint) || rr < isPrint[i&^1] || isPrint[i|1] < rr {
+		return false
+	}
+	if r >= 0x20000 {
+		return true
+	}
+	r -= 0x10000
+	j := bsearch16(isNotPrint, uint16(r))
+	return j >= len(isNotPrint) || isNotPrint[j] != uint16(r)
+}