@@ -76,3 +76,43 @@ func (h Header) WriteSubset(w io.Writer, exclude map[string]bool) error {
7676// the rest are converted to lowercase. For example, the
7777// canonical key for "accept-encoding" is "Accept-Encoding".
7878func CanonicalHeaderKey (s string )string {return textproto .CanonicalMIMEHeaderKey (s ) }
79+
80+ // hasToken returns whether token appears with v, ASCII
81+ // case-insensitive, with space or comma boundaries.
82+ // token must be all lowercase.
83+ // v may contain mixed cased.
84+ func hasToken (v ,token string )bool {
85+ if len (token )> len (v )|| token == "" {
86+ return false
87+ }
88+ if v == token {
89+ return true
90+ }
91+ for sp := 0 ;sp <= len (v )- len (token );sp ++ {
92+ // Check that first character is good.
93+ // The token is ASCII, so checking only a single byte
94+ // is sufficient. We skip this potential starting
95+ // position if both the first byte and its potential
96+ // ASCII uppercase equivalent (b|0x20) don't match.
97+ // False positives ('^' => '~') are caught by EqualFold.
98+ if b := v [sp ];b != token [0 ]&& b | 0x20 != token [0 ] {
99+ continue
100+ }
101+ // Check that start pos is on a valid token boundary.
102+ if sp > 0 && ! isTokenBoundary (v [sp - 1 ]) {
103+ continue
104+ }
105+ // Check that end pos is on a valid token boundary.
106+ if endPos := sp + len (token );endPos != len (v )&& ! isTokenBoundary (v [endPos ]) {
107+ continue
108+ }
109+ if strings .EqualFold (v [sp :sp + len (token )],token ) {
110+ return true
111+ }
112+ }
113+ return false
114+ }
115+
116+ func isTokenBoundary (b byte )bool {
117+ return b == ' ' || b == ',' || b == '\t'
118+ }