at now
for determine connection lost (iPhone hasn't keepalive ops for socket) I do next:
if App dont recv any datas on channels over 6seconds it send:
"{"op":"ping"}"
if connection is ok than server responds to App:
{"message":"Unknown command","op":"remark","success":false}
if no any responds in next 6seconds (include other datas on channels) App decides that current connection lost and try to create new connection (with close old)
NB: "ping" dont send every 6seconds! only if at last 6seconds no datas (including "Unknown command")
otherwise App works but nothing shows over hour on broken connection (turnoff WAN at router). I dont known default values in iPhone keep-alive logic.
and my suggestion:
maybe add "good" response:
{"op":"pong"}
it dont requires any logic or DB-access. simple response for current connection
although its works well now