code: public static void setKeepAlive(HttpMessage message, boolean keepAlive) {
          setKeepAlive(message.headers(), message.protocolVersion(), keepAlive);
      }
docs: Sets the value of the {@code "Connection"} header depending on the
  protocol version of the specified message. This getMethod sets or removes
  the {@code "Connection"} header depending on what the default keep alive
  mode of the message's protocol version is, as specified by
  {@link HttpVersion#isKeepAliveDefault()}.
  <ul>
  <li>If the connection is kept alive by default:
  <ul>
  <li>set to {@code "close"} if {@code keepAlive} is {@code false}.</li>
  <li>remove otherwise.</li>
  </ul></li>
  <li>If the connection is closed by default:
  <ul>
  <li>set to {@code "keep-alive"} if {@code keepAlive} is {@code true}.</li>
  <li>remove otherwise.</li>
  </ul></li>
  </ul>
  @see #setKeepAlive(HttpHeaders, HttpVersion, boolean)