net/http: correct and faster hasToken

Fixes #3535

R=golang-dev, dsymonds
CC=golang-dev
https://golang.org/cl/6245060

src/pkg/net/http/header.go

@@ -76,3 +76,38 @@ func (h Header) WriteSubset(w io.Writer, exclude map[string]bool) error {
 // the rest are converted to lowercase.  For example, the
 // canonical key for "accept-encoding" is "Accept-Encoding".
 func CanonicalHeaderKey(s string) string { return textproto.CanonicalMIMEHeaderKey(s) }
+
+// hasToken returns whether token appears with v, ASCII
+// case-insensitive, with space or comma boundaries.
+// token must be all lowercase.
+// v may contain mixed cased.
+func hasToken(v, token string) bool {
+	if len(token) > len(v) || token == "" {
+		return false
+	}
+	if v == token {
+		return true
+	}
+	for sp := 0; sp <= len(v)-len(token); sp++ {
+		// Check that first character is good.
+		if b := v[sp]; b != token[0] && b|0x20 != token[0] {
+			continue
+		}
+		// Check that start pos is on a valid token boundary.
+		if sp > 0 && !isTokenBoundary(v[sp-1]) {
+			continue
+		}
+		// Check that end pos is on a valid token boundary.
+		if endPos := sp + len(token); endPos != len(v) && !isTokenBoundary(v[endPos]) {
+			continue
+		}
+		if strings.EqualFold(v[sp:sp+len(token)], token) {
+			return true
+		}
+	}
+	return false
+}
+
+func isTokenBoundary(b byte) bool {
+	return b == ' ' || b == ',' || b == '\t'
+}

src/pkg/net/http/header_test.go

@@ -79,3 +79,46 @@ func TestHeaderWrite(t *testing.T) {
 		buf.Reset()
 	}
 }
+
+type hasTokenTest struct {
+	header string
+	token  string
+	want   bool
+}
+
+var hasTokenTests = []hasTokenTest{
+	{"", "", false},
+	{"", "foo", false},
+	{"foo", "foo", true},
+	{"foo ", "foo", true},
+	{" foo", "foo", true},
+	{" foo ", "foo", true},
+	{"foo,bar", "foo", true},
+	{"bar,foo", "foo", true},
+	{"bar, foo", "foo", true},
+	{"bar,foo, baz", "foo", true},
+	{"bar, foo,baz", "foo", true},
+	{"bar,foo, baz", "foo", true},
+	{"bar, foo, baz", "foo", true},
+	{"FOO", "foo", true},
+	{"FOO ", "foo", true},
+	{" FOO", "foo", true},
+	{" FOO ", "foo", true},
+	{"FOO,BAR", "foo", true},
+	{"BAR,FOO", "foo", true},
+	{"BAR, FOO", "foo", true},
+	{"BAR,FOO, baz", "foo", true},
+	{"BAR, FOO,BAZ", "foo", true},
+	{"BAR,FOO, BAZ", "foo", true},
+	{"BAR, FOO, BAZ", "foo", true},
+	{"foobar", "foo", false},
+	{"barfoo ", "foo", false},
+}
+
+func TestHasToken(t *testing.T) {
+	for _, tt := range hasTokenTests {
+		if hasToken(tt.header, tt.token) != tt.want {
+			t.Errorf("hasToken(%q, %q) = %v; want %v", tt.header, tt.token, !tt.want, tt.want)
+		}
+	}
+}

src/pkg/net/http/request.go

@@ -745,11 +745,3 @@ func (r *Request) wantsHttp10KeepAlive() bool {
 func (r *Request) wantsClose() bool {
 	return hasToken(r.Header.Get("Connection"), "close")
 }
-
-func hasToken(s, token string) bool {
-	if s == "" {
-		return false
-	}
-	// TODO This is a poor implementation of the RFC. See http://golang.org/issue/3535
-	return strings.Contains(strings.ToLower(s), token)
-}