code: func isH2CUpgrade(h http.Header) bool {
  	return httpguts.HeaderValuesContainsToken(h[textproto.CanonicalMIMEHeaderKey("Upgrade")], "h2c") &&
  		httpguts.HeaderValuesContainsToken(h[textproto.CanonicalMIMEHeaderKey("Connection")], "HTTP2-Settings")
  }
docs: // isH2CUpgrade returns true if the header properly request an upgrade to h2c
  // as specified by Section 3.2.