libgo/go/html/template/css.go

   1 // Copyright 2011 The Go Authors. All rights reserved.
   2 // Use of this source code is governed by a BSD-style
   3 // license that can be found in the LICENSE file.
   4
   5 package template
   6
   7 import (
   8         "bytes"
   9         "fmt"
  10         "unicode"
  11         "unicode/utf8"
  12 )
  13
  14 // endsWithCSSKeyword reports whether b ends with an ident that
  15 // case-insensitively matches the lower-case kw.
  16 func endsWithCSSKeyword(b []byte, kw string) bool {
  17         i := len(b) - len(kw)
  18         if i < 0 {
  19                 // Too short.
  20                 return false
  21         }
  22         if i != 0 {
  23                 r, _ := utf8.DecodeLastRune(b[:i])
  24                 if isCSSNmchar(r) {
  25                         // Too long.
  26                         return false
  27                 }
  28         }
  29         // Many CSS keywords, such as "!important" can have characters encoded,
  30         // but the URI production does not allow that according to
  31         // http://www.w3.org/TR/css3-syntax/#TOK-URI
  32         // This does not attempt to recognize encoded keywords. For example,
  33         // given "\75\72\6c" and "url" this return false.
  34         return string(bytes.ToLower(b[i:])) == kw
  35 }
  36
  37 // isCSSNmchar reports whether rune is allowed anywhere in a CSS identifier.
  38 func isCSSNmchar(r rune) bool {
  39         // Based on the CSS3 nmchar production but ignores multi-rune escape
  40         // sequences.
  41         // http://www.w3.org/TR/css3-syntax/#SUBTOK-nmchar
  42         return 'a' <= r && r <= 'z' ||
  43                 'A' <= r && r <= 'Z' ||
  44                 '0' <= r && r <= '9' ||
  45                 r == '-' ||
  46                 r == '_' ||
  47                 // Non-ASCII cases below.
  48                 0x80 <= r && r <= 0xd7ff ||
  49                 0xe000 <= r && r <= 0xfffd ||
  50                 0x10000 <= r && r <= 0x10ffff
  51 }
  52
  53 // decodeCSS decodes CSS3 escapes given a sequence of stringchars.
  54 // If there is no change, it returns the input, otherwise it returns a slice
  55 // backed by a new array.
  56 // http://www.w3.org/TR/css3-syntax/#SUBTOK-stringchar defines stringchar.
  57 func decodeCSS(s []byte) []byte {
  58         i := bytes.IndexByte(s, '\\')
  59         if i == -1 {
  60                 return s
  61         }
  62         // The UTF-8 sequence for a codepoint is never longer than 1 + the
  63         // number hex digits need to represent that codepoint, so len(s) is an
  64         // upper bound on the output length.
  65         b := make([]byte, 0, len(s))
  66         for len(s) != 0 {
  67                 i := bytes.IndexByte(s, '\\')
  68                 if i == -1 {
  69                         i = len(s)
  70                 }
  71                 b, s = append(b, s[:i]...), s[i:]
  72                 if len(s) < 2 {
  73                         break
  74                 }
  75                 // http://www.w3.org/TR/css3-syntax/#SUBTOK-escape
  76                 // escape ::= unicode | '\' [#x20-#x7E#x80-#xD7FF#xE000-#xFFFD#x10000-#x10FFFF]
  77                 if isHex(s[1]) {
  78                         // http://www.w3.org/TR/css3-syntax/#SUBTOK-unicode
  79                         //   unicode ::= '\' [0-9a-fA-F]{1,6} wc?
  80                         j := 2
  81                         for j < len(s) && j < 7 && isHex(s[j]) {
  82                                 j++
  83                         }
  84                         r := hexDecode(s[1:j])
  85                         if r > unicode.MaxRune {
  86                                 r, j = r/16, j-1
  87                         }
  88                         n := utf8.EncodeRune(b[len(b):cap(b)], r)
  89                         // The optional space at the end allows a hex
  90                         // sequence to be followed by a literal hex.
  91                         // string(decodeCSS([]byte(`\A B`))) == "\nB"
  92                         b, s = b[:len(b)+n], skipCSSSpace(s[j:])
  93                 } else {
  94                         // `\\` decodes to `\` and `\"` to `"`.
  95                         _, n := utf8.DecodeRune(s[1:])
  96                         b, s = append(b, s[1:1+n]...), s[1+n:]
  97                 }
  98         }
  99         return b
 100 }
 101
 102 // isHex reports whether the given character is a hex digit.
 103 func isHex(c byte) bool {
 104         return '0' <= c && c <= '9' || 'a' <= c && c <= 'f' || 'A' <= c && c <= 'F'
 105 }
 106
 107 // hexDecode decodes a short hex digit sequence: "10" -> 16.
 108 func hexDecode(s []byte) rune {
 109         n := '\x00'
 110         for _, c := range s {
 111                 n <<= 4
 112                 switch {
 113                 case '0' <= c && c <= '9':
 114                         n |= rune(c - '0')
 115                 case 'a' <= c && c <= 'f':
 116                         n |= rune(c-'a') + 10
 117                 case 'A' <= c && c <= 'F':
 118                         n |= rune(c-'A') + 10
 119                 default:
 120                         panic(fmt.Sprintf("Bad hex digit in %q", s))
 121                 }
 122         }
 123         return n
 124 }
 125
 126 // skipCSSSpace returns a suffix of c, skipping over a single space.
 127 func skipCSSSpace(c []byte) []byte {
 128         if len(c) == 0 {
 129                 return c
 130         }
 131         // wc ::= #x9 | #xA | #xC | #xD | #x20
 132         switch c[0] {
 133         case '\t', '\n', '\f', ' ':
 134                 return c[1:]
 135         case '\r':
 136                 // This differs from CSS3's wc production because it contains a
 137                 // probable spec error whereby wc contains all the single byte
 138                 // sequences in nl (newline) but not CRLF.
 139                 if len(c) >= 2 && c[1] == '\n' {
 140                         return c[2:]
 141                 }
 142                 return c[1:]
 143         }
 144         return c
 145 }
 146
 147 // isCSSSpace reports whether b is a CSS space char as defined in wc.
 148 func isCSSSpace(b byte) bool {
 149         switch b {
 150         case '\t', '\n', '\f', '\r', ' ':
 151                 return true
 152         }
 153         return false
 154 }
 155
 156 // cssEscaper escapes HTML and CSS special characters using \<hex>+ escapes.
 157 func cssEscaper(args ...interface{}) string {
 158         s, _ := stringify(args...)
 159         var b bytes.Buffer
 160         r, w, written := rune(0), 0, 0
 161         for i := 0; i < len(s); i += w {
 162                 // See comment in htmlEscaper.
 163                 r, w = utf8.DecodeRuneInString(s[i:])
 164                 var repl string
 165                 switch {
 166                 case int(r) < len(cssReplacementTable) && cssReplacementTable[r] != "":
 167                         repl = cssReplacementTable[r]
 168                 default:
 169                         continue
 170                 }
 171                 b.WriteString(s[written:i])
 172                 b.WriteString(repl)
 173                 written = i + w
 174                 if repl != `\\` && (written == len(s) || isHex(s[written]) || isCSSSpace(s[written])) {
 175                         b.WriteByte(' ')
 176                 }
 177         }
 178         if written == 0 {
 179                 return s
 180         }
 181         b.WriteString(s[written:])
 182         return b.String()
 183 }
 184
 185 var cssReplacementTable = []string{
 186         0:    `\0`,
 187         '\t': `\9`,
 188         '\n': `\a`,
 189         '\f': `\c`,
 190         '\r': `\d`,
 191         // Encode HTML specials as hex so the output can be embedded
 192         // in HTML attributes without further encoding.
 193         '"':  `\22`,
 194         '&':  `\26`,
 195         '\'': `\27`,
 196         '(':  `\28`,
 197         ')':  `\29`,
 198         '+':  `\2b`,
 199         '/':  `\2f`,
 200         ':':  `\3a`,
 201         ';':  `\3b`,
 202         '<':  `\3c`,
 203         '>':  `\3e`,
 204         '\\': `\\`,
 205         '{':  `\7b`,
 206         '}':  `\7d`,
 207 }
 208
 209 var expressionBytes = []byte("expression")
 210 var mozBindingBytes = []byte("mozbinding")
 211
 212 // cssValueFilter allows innocuous CSS values in the output including CSS
 213 // quantities (10px or 25%), ID or class literals (#foo, .bar), keyword values
 214 // (inherit, blue), and colors (#888).
 215 // It filters out unsafe values, such as those that affect token boundaries,
 216 // and anything that might execute scripts.
 217 func cssValueFilter(args ...interface{}) string {
 218         s, t := stringify(args...)
 219         if t == contentTypeCSS {
 220                 return s
 221         }
 222         b, id := decodeCSS([]byte(s)), make([]byte, 0, 64)
 223
 224         // CSS3 error handling is specified as honoring string boundaries per
 225         // http://www.w3.org/TR/css3-syntax/#error-handling :
 226         //     Malformed declarations. User agents must handle unexpected
 227         //     tokens encountered while parsing a declaration by reading until
 228         //     the end of the declaration, while observing the rules for
 229         //     matching pairs of (), [], {}, "", and '', and correctly handling
 230         //     escapes. For example, a malformed declaration may be missing a
 231         //     property, colon (:) or value.
 232         // So we need to make sure that values do not have mismatched bracket
 233         // or quote characters to prevent the browser from restarting parsing
 234         // inside a string that might embed JavaScript source.
 235         for i, c := range b {
 236                 switch c {
 237                 case 0, '"', '\'', '(', ')', '/', ';', '@', '[', '\\', ']', '`', '{', '}':
 238                         return filterFailsafe
 239                 case '-':
 240                         // Disallow <!-- or -->.
 241                         // -- should not appear in valid identifiers.
 242                         if i != 0 && b[i-1] == '-' {
 243                                 return filterFailsafe
 244                         }
 245                 default:
 246                         if c < utf8.RuneSelf && isCSSNmchar(rune(c)) {
 247                                 id = append(id, c)
 248                         }
 249                 }
 250         }
 251         id = bytes.ToLower(id)
 252         if bytes.Contains(id, expressionBytes) || bytes.Contains(id, mozBindingBytes) {
 253                 return filterFailsafe
 254         }
 255         return string(b)
 256 }