e message is known to have no payload.
                  The function shall not exit via an exception.
                </p>
                <p>
                  When this function is present:
                </p>
                <p>
                  * The function shall not fail
                </p>
                <p>
                  * A call to <a class="link" href="../ref/boost__beast__http__message/payload_size.html" title="http::message::payload_size"><code class="computeroutput"><span class="ident