code: public synchronized void addProtocol(String productString, HttpUpgradeListener openListener, final HttpUpgradeHandshake handshake) {
          addProtocol(productString, openListener, null, handshake);
      }
docs: Add a protocol to this handler.
  
  @param productString the product string to match
  @param openListener  the open listener to call
  @param handshake     a handshake implementation that can be used to verify the client request and modify the response