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// 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.
package strconv
import (
"bytes"
"os"
"strings"
"unicode"
"utf8"
)
const lowerhex = "0123456789abcdef"
func quoteWith(s string, quote byte, ASCIIonly bool) string {
var buf bytes.Buffer
buf.WriteByte(quote)
for width := 0; len(s) > 0; s = s[width:] {
rune := int(s[0])
width = 1
if rune >= utf8.RuneSelf {
rune, width = utf8.DecodeRuneInString(s)
}
if width == 1 && rune == utf8.RuneError {
buf.WriteString(`\x`)
buf.WriteByte(lowerhex[s[0]>>4])
buf.WriteByte(lowerhex[s[0]&0xF])
continue
}
if rune == int(quote) || rune == '\\' { // always backslashed
buf.WriteByte('\\')
buf.WriteByte(byte(rune))
continue
}
if ASCIIonly {
if rune <= unicode.MaxASCII && unicode.IsPrint(rune) {
buf.WriteRune(rune)
continue
}
} else if unicode.IsPrint(rune) {
buf.WriteRune(rune)
continue
}
switch rune {
case '\a':
buf.WriteString(`\a`)
case '\b':
buf.WriteString(`\b`)
case '\f':
buf.WriteString(`\f`)
case '\n':
buf.WriteString(`\n`)
case '\r':
buf.WriteString(`\r`)
case '\t':
buf.WriteString(`\t`)
case '\v':
buf.WriteString(`\v`)
default:
switch {
case rune < ' ':
buf.WriteString(`\x`)
buf.WriteByte(lowerhex[s[0]>>4])
buf.WriteByte(lowerhex[s[0]&0xF])
case rune > unicode.MaxRune:
rune = 0xFFFD
fallthrough
case rune < 0x10000:
buf.WriteString(`\u`)
for s := 12; s >= 0; s -= 4 {
buf.WriteByte(lowerhex[rune>>uint(s)&0xF])
}
default:
buf.WriteString(`\U`)
for s := 28; s >= 0; s -= 4 {
buf.WriteByte(lowerhex[rune>>uint(s)&0xF])
}
}
}
}
buf.WriteByte(quote)
return buf.String()
}
// 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
// unicode.IsPrint.
func Quote(s string) string {
return quoteWith(s, '"', false)
}
// 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
// unicode.IsPrint.
func QuoteToASCII(s string) string {
return quoteWith(s, '"', true)
}
// 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
// unicode.IsPrint.
func QuoteRune(rune int) string {
// TODO: avoid the allocation here.
return quoteWith(string(rune), '\'', false)
}
// 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 unicode.IsPrint.
func QuoteRuneToASCII(rune int) string {
// TODO: avoid the allocation here.
return quoteWith(string(rune), '\'', true)
}
// CanBackquote returns whether the string s would be
// a valid Go string literal if enclosed in backquotes.
func CanBackquote(s string) bool {
for i := 0; i < len(s); i++ {
if (s[i] < ' ' && s[i] != '\t') || s[i] == '`' {
return false
}
}
return true
}
func unhex(b byte) (v int, ok bool) {
c := int(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 int, multibyte bool, tail string, err os.Error) {
// easy cases
switch c := s[0]; {
case c == quote && (quote == '\'' || quote == '"'):
err = os.EINVAL
return
case c >= utf8.RuneSelf:
r, size := utf8.DecodeRuneInString(s)
return r, true, s[size:], nil
case c != '\\':
return int(s[0]), false, s[1:], nil
}
// hard case: c is backslash
if len(s) <= 1 {
err = os.EINVAL
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
}
v := 0
if len(s) < n {
err = os.EINVAL
return
}
for j := 0; j < n; j++ {
x, ok := unhex(s[j])
if !ok {
err = os.EINVAL
return
}
v = v<<4 | x
}
s = s[n:]
if c == 'x' {
// single-byte string, possibly not UTF-8
value = v
break
}
if v > unicode.MaxRune {
err = os.EINVAL
return
}
value = v
multibyte = true
case '0', '1', '2', '3', '4', '5', '6', '7':
v := int(c) - '0'
if len(s) < 2 {
err = os.EINVAL
return
}
for j := 0; j < 2; j++ { // one digit already; two more
x := int(s[j]) - '0'
if x < 0 || x > 7 {
return
}
v = (v << 3) | x
}
s = s[2:]
if v > 255 {
err = os.EINVAL
return
}
value = v
case '\\':
value = '\\'
case '\'', '"':
if c != quote {
err = os.EINVAL
return
}
value = int(c)
default:
err = os.EINVAL
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 os.Error) {
n := len(s)
if n < 2 {
return "", os.EINVAL
}
quote := s[0]
if quote != s[n-1] {
return "", os.EINVAL
}
s = s[1 : n-1]
if quote == '`' {
if strings.Contains(s, "`") {
return "", os.EINVAL
}
return s, nil
}
if quote != '"' && quote != '\'' {
return "", os.EINVAL
}
var buf bytes.Buffer
for len(s) > 0 {
c, multibyte, ss, err := UnquoteChar(s, quote)
if err != nil {
return "", err
}
s = ss
if c < utf8.RuneSelf || !multibyte {
buf.WriteByte(byte(c))
} else {
buf.WriteString(string(c))
}
if quote == '\'' && len(s) != 0 {
// single-quoted must be single character
return "", os.EINVAL
}
}
return buf.String(), nil
}