typedef axl_bool(* MyQttOnHeaderReceived)(MyQttCtx *ctx, MyQttConn *conn, MyQttMsg *msg, axlPointer user_data)

Async notification handler called when the message header is received (and before receiving the rest of the message).

ctxThe context where the operation takes place.
connThe connection where the operation is taking place.
msgThe message that contains hearder information. Keep in mind that this reference is still not well defined (for example, it doesn't have the entire message yet, but it contains all the header indications like type, qos, dup, retain and size.
user_dataUser data pointer defined at the time this handler was configured.
axl_true to allow accepting the message. Return axl_false to cause the message to be not accepted and to close the connection that sent the message (there is no way to communicate sending party that the message is not going to be accepted).