_, _ = w.Write([]byte("h2c upgrade not allowed"))
			return
		}
		h.ServeHTTP(w, r)
	})
}

func isH2CUpgrade(h http.Header) bool {
	return httpguts.HeaderValuesContainsToken(h[textproto.CanonicalMIMEHeaderKey("Upgrade")], "h2c") &&
		httpguts.HeaderValuesContainsToken(h[textproto.CanonicalMIMEHeaderKey("Connection")], "HTTP2-Settings")

	'z':  true,
	'|':  true,
	'~':  true,
}

func IsTokenRune(r rune) bool {
	return r < utf8.RuneSelf && isTokenTable[byte(r)]
}

// HeaderValuesContainsToken reports whether any string in values
// contains the provided token, ASCII case-insensitively.
func HeaderValuesContainsToken(values []string, token string) bool {
	for _, v := range values {
		if headerValueContainsToken(v, token) {
			return true
		}
	}