[sr-dev] [kamailio/kamailio] Memory leaks in websocket module (#1892)

[Andrey Deykunov]

### Description

We had Kamailio 5.1.4 with websocket module. Unfortunately, our clients don't support websocket keepalive mechanism at all, so I used TCP keepalive instead with the following parameters:

```
tcp_keepalive=yes
tcp_keepcnt=6
tcp_keepidle=60
tcp_keepintvl=10
```


and set up KEEPALIVE_MECHANISM_NONE:

`modparam("websocket", "keepalive_mechanism", 0)`


During load testing and debugging, when 8k clients sent registrations, it was found out that shared memory was not freed after closing connections (_ws_connection_list_t *wsconn_used_list_ variable in ws_conn.c ).


### Possible Solutions

I've decided to add new keepalive mechanism that periodically checks TCP connection related to websocket:

```
enum
{
    KEEPALIVE_MECHANISM_NONE = 0,
    KEEPALIVE_MECHANISM_PING = 1,
    KEEPALIVE_MECHANISM_PONG = 2,
    KEEPALIVE_MECHANISM_TCP_CONN_CHECK = 3
};  
```


and added the line to config:

```
# Enable custom tcp-connection-health based keepalive mechanism (3)
# KEEPALIVE_MECHANISM_NONE = 0,
# KEEPALIVE_MECHANISM_PING = 1,
# KEEPALIVE_MECHANISM_PONG = 2
# KEEPALIVE_MECHANISM_TCP_CONN_CHECK = 3
modparam("websocket", "keepalive_mechanism", 3)
```


Also, I've implemented the mechanism in ws_keepalive function:

```
void ws_keepalive(unsigned int ticks, void *param)
{
    int check_time =
            (int)time(NULL) - cfg_get(websocket, ws_cfg, keepalive_timeout);

    ws_connection_t **list = NULL, **list_head = NULL;
    ws_connection_t *wsc = NULL;

    /* get an array of pointer to all ws connection */
    list_head = wsconn_get_list();
    if(!list_head)
        return;

    list = list_head;
    wsc = *list_head;
    while(wsc && wsc->last_used < check_time) {
        if (ws_keepalive_mechanism == KEEPALIVE_MECHANISM_TCP_CONN_CHECK) {
            struct tcp_connection *con = tcpconn_get(wsc->id, 0, 0, 0, 0);
            if(!con) {
                LM_INFO("tcp connection has been lost\n");
                wsc->state = WS_S_CLOSING;
            }
        }

        if(wsc->state == WS_S_CLOSING || wsc->awaiting_pong) {
            LM_INFO("forcibly closing connection\n");
            wsconn_close_now(wsc);
        } else {
            int opcode = (ws_keepalive_mechanism == KEEPALIVE_MECHANISM_PING)
                                ? OPCODE_PING
                                : OPCODE_PONG;
            ping_pong(wsc, opcode);
        }

        wsc = *(++list);
    }

    wsconn_put_list(list_head);
}

```

and changed memory allocation method in wsconn_get_list and wsconn_put_list methods from pkg to shm, because, as it turned out during load testing, using pkg_malloc (the C malloc) in this functions may cousing fails under serious loads.

These modifications solved the problem. But about a week ago we've started switching to ver. 5.2.1 and found a lot of changes in the websocket module. So, I've added my changes in this commit https://github.com/korizza/kamailio/commit/b3e03d03574ff4ff076005bb8a01d7461af2f8f5 . Please take a look.



### Additional Information

Adding ws_conn_put_id in this commit https://github.com/kamailio/kamailio/commit/a975bca1702ea2f3db47f834f7e4da2786ced201#diff-59c50f19ab1ccf4afe10617cdc346bc2 did not solve problem with ref counter increasing.


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