When I enable SIP.js keep-alive, it sends double CR-LFs to Kamailio via websocket, however Kamailio understands it as a malformed SIP message, and therefore does not reply with a single CR-LF.
Debug log from websocket module upon arrival of keep-alive:
`15(88) DEBUG: websocket [ws_frame.c:415]: decode_and_validate_ws_frame(): decoding WebSocket frame` `15(88) DEBUG: websocket [ws_frame.c:451]: decode_and_validate_ws_frame(): supported non-control frame: 0x1` `15(88) DEBUG: websocket [ws_frame.c:550]: decode_and_validate_ws_frame(): Rx (decoded):` ` ` `15(88) DEBUG: websocket [ws_frame.c:684]: ws_frame_receive(): Rx SIP message:` ` ` ` ` `15(88) DEBUG: websocket [ws_conn.c:383]: wsconn_put(): wsconn_put start for [0x7fc8cbd45860] refcnt [2]` `15(88) DEBUG: websocket [ws_conn.c:416]: wsconn_put(): wsconn_put end for [0x7fc8cbd45860] refcnt [1]` `15(88) INFO: <core> [parser/parse_fline.c:87]: parse_first_line(): ERROR: parse_first_line: message too short: 0` `15(88) ERROR: <core> [parser/parse_fline.c:257]: parse_first_line(): parse_first_line: bad message (offset: 0)` `15(88) ERROR: <core> [parser/msg_parser.c:671]: parse_msg(): ERROR: parse_msg: message=<` ` ` `>` `15(88) ERROR: <core> [receive.c:173]: receive_msg(): core parsing of SIP message failed (10.0.1.73:1043/6)`