269 lines
7.0 KiB
Go
269 lines
7.0 KiB
Go
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// Copyright 2011 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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package html
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import (
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"bytes"
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"fmt"
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"unicode"
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"utf8"
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)
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// endsWithCSSKeyword returns whether b ends with an ident that
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// case-insensitively matches the lower-case kw.
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func endsWithCSSKeyword(b []byte, kw string) bool {
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i := len(b) - len(kw)
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if i < 0 {
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// Too short.
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return false
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}
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if i != 0 {
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r, _ := utf8.DecodeLastRune(b[:i])
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if isCSSNmchar(r) {
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// Too long.
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return false
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}
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}
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// Many CSS keywords, such as "!important" can have characters encoded,
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// but the URI production does not allow that according to
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// http://www.w3.org/TR/css3-syntax/#TOK-URI
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// This does not attempt to recognize encoded keywords. For example,
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// given "\75\72\6c" and "url" this return false.
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return string(bytes.ToLower(b[i:])) == kw
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}
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// isCSSNmchar returns whether rune is allowed anywhere in a CSS identifier.
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func isCSSNmchar(rune int) bool {
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// Based on the CSS3 nmchar production but ignores multi-rune escape
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// sequences.
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// http://www.w3.org/TR/css3-syntax/#SUBTOK-nmchar
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return 'a' <= rune && rune <= 'z' ||
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'A' <= rune && rune <= 'Z' ||
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'0' <= rune && rune <= '9' ||
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'-' == rune ||
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'_' == rune ||
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// Non-ASCII cases below.
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0x80 <= rune && rune <= 0xd7ff ||
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0xe000 <= rune && rune <= 0xfffd ||
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0x10000 <= rune && rune <= 0x10ffff
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}
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// decodeCSS decodes CSS3 escapes given a sequence of stringchars.
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// If there is no change, it returns the input, otherwise it returns a slice
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// backed by a new array.
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// http://www.w3.org/TR/css3-syntax/#SUBTOK-stringchar defines stringchar.
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func decodeCSS(s []byte) []byte {
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i := bytes.IndexByte(s, '\\')
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if i == -1 {
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return s
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}
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// The UTF-8 sequence for a codepoint is never longer than 1 + the
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// number hex digits need to represent that codepoint, so len(s) is an
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// upper bound on the output length.
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b := make([]byte, 0, len(s))
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for len(s) != 0 {
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i := bytes.IndexByte(s, '\\')
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if i == -1 {
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i = len(s)
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}
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b, s = append(b, s[:i]...), s[i:]
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if len(s) < 2 {
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break
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}
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// http://www.w3.org/TR/css3-syntax/#SUBTOK-escape
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// escape ::= unicode | '\' [#x20-#x7E#x80-#xD7FF#xE000-#xFFFD#x10000-#x10FFFF]
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if isHex(s[1]) {
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// http://www.w3.org/TR/css3-syntax/#SUBTOK-unicode
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// unicode ::= '\' [0-9a-fA-F]{1,6} wc?
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j := 2
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for j < len(s) && j < 7 && isHex(s[j]) {
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j++
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}
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rune := hexDecode(s[1:j])
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if rune > unicode.MaxRune {
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rune, j = rune/16, j-1
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}
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n := utf8.EncodeRune(b[len(b):cap(b)], rune)
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// The optional space at the end allows a hex
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// sequence to be followed by a literal hex.
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// string(decodeCSS([]byte(`\A B`))) == "\nB"
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b, s = b[:len(b)+n], skipCSSSpace(s[j:])
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} else {
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// `\\` decodes to `\` and `\"` to `"`.
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_, n := utf8.DecodeRune(s[1:])
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b, s = append(b, s[1:1+n]...), s[1+n:]
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}
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}
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return b
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}
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// isHex returns whether the given character is a hex digit.
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func isHex(c byte) bool {
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return '0' <= c && c <= '9' || 'a' <= c && c <= 'f' || 'A' <= c && c <= 'F'
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}
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// hexDecode decodes a short hex digit sequence: "10" -> 16.
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func hexDecode(s []byte) int {
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n := 0
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for _, c := range s {
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n <<= 4
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switch {
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case '0' <= c && c <= '9':
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n |= int(c - '0')
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case 'a' <= c && c <= 'f':
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n |= int(c-'a') + 10
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case 'A' <= c && c <= 'F':
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n |= int(c-'A') + 10
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default:
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panic(fmt.Sprintf("Bad hex digit in %q", s))
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}
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}
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return n
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}
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// skipCSSSpace returns a suffix of c, skipping over a single space.
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func skipCSSSpace(c []byte) []byte {
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if len(c) == 0 {
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return c
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}
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// wc ::= #x9 | #xA | #xC | #xD | #x20
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switch c[0] {
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case '\t', '\n', '\f', ' ':
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return c[1:]
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case '\r':
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// This differs from CSS3's wc production because it contains a
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// probable spec error whereby wc contains all the single byte
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// sequences in nl (newline) but not CRLF.
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if len(c) >= 2 && c[1] == '\n' {
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return c[2:]
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}
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return c[1:]
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}
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return c
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}
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// isCSSSpace returns whether b is a CSS space char as defined in wc.
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func isCSSSpace(b byte) bool {
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switch b {
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case '\t', '\n', '\f', '\r', ' ':
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return true
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}
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return false
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}
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// cssEscaper escapes HTML and CSS special characters using \<hex>+ escapes.
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func cssEscaper(args ...interface{}) string {
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s, _ := stringify(args...)
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var b bytes.Buffer
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written := 0
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for i, r := range s {
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var repl string
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switch r {
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case 0:
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repl = `\0`
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case '\t':
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repl = `\9`
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case '\n':
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repl = `\a`
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case '\f':
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repl = `\c`
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case '\r':
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repl = `\d`
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// Encode HTML specials as hex so the output can be embedded
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// in HTML attributes without further encoding.
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case '"':
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repl = `\22`
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case '&':
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repl = `\26`
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case '\'':
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repl = `\27`
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case '(':
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repl = `\28`
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case ')':
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repl = `\29`
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case '+':
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repl = `\2b`
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case '/':
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repl = `\2f`
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case ':':
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repl = `\3a`
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case ';':
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repl = `\3b`
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case '<':
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repl = `\3c`
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case '>':
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repl = `\3e`
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case '\\':
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repl = `\\`
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case '{':
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repl = `\7b`
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case '}':
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repl = `\7d`
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default:
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continue
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}
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b.WriteString(s[written:i])
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b.WriteString(repl)
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written = i + utf8.RuneLen(r)
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if repl != `\\` && (written == len(s) || isHex(s[written]) || isCSSSpace(s[written])) {
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b.WriteByte(' ')
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}
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}
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if written == 0 {
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return s
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}
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b.WriteString(s[written:])
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return b.String()
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}
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var expressionBytes = []byte("expression")
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var mozBindingBytes = []byte("mozbinding")
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// cssValueFilter allows innocuous CSS values in the output including CSS
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// quantities (10px or 25%), ID or class literals (#foo, .bar), keyword values
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// (inherit, blue), and colors (#888).
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// It filters out unsafe values, such as those that affect token boundaries,
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// and anything that might execute scripts.
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func cssValueFilter(args ...interface{}) string {
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s, t := stringify(args...)
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if t == contentTypeCSS {
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return s
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}
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b, id := decodeCSS([]byte(s)), make([]byte, 0, 64)
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// CSS3 error handling is specified as honoring string boundaries per
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// http://www.w3.org/TR/css3-syntax/#error-handling :
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// Malformed declarations. User agents must handle unexpected
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// tokens encountered while parsing a declaration by reading until
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// the end of the declaration, while observing the rules for
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// matching pairs of (), [], {}, "", and '', and correctly handling
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// escapes. For example, a malformed declaration may be missing a
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// property, colon (:) or value.
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// So we need to make sure that values do not have mismatched bracket
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// or quote characters to prevent the browser from restarting parsing
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// inside a string that might embed JavaScript source.
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for i, c := range b {
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switch c {
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case 0, '"', '\'', '(', ')', '/', ';', '@', '[', '\\', ']', '`', '{', '}':
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return filterFailsafe
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case '-':
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// Disallow <!-- or -->.
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// -- should not appear in valid identifiers.
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if i != 0 && '-' == b[i-1] {
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return filterFailsafe
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}
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default:
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if c < 0x80 && isCSSNmchar(int(c)) {
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id = append(id, c)
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}
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}
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}
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id = bytes.ToLower(id)
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if bytes.Index(id, expressionBytes) != -1 || bytes.Index(id, mozBindingBytes) != -1 {
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return filterFailsafe
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}
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return string(b)
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}
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