io: use GDateTime for formatting timestamp for websock headers

The GDateTime APIs provided by GLib avoid portability pitfalls, such
as some platforms where 'struct timeval.tv_sec' field is still 'long'
instead of 'time_t'. When combined with automatic cleanup, GDateTime
often results in simpler code too.

Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>

io/channel-websock.c

@@ -177,15 +177,9 @@ qio_channel_websock_handshake_send_res(QIOChannelWebsock *ioc,
 
 static gchar *qio_channel_websock_date_str(void)
 {
-    struct tm tm;
-    time_t now = time(NULL);
-    char datebuf[128];
+    g_autoptr(GDateTime) now = g_date_time_new_now_utc();
 
-    gmtime_r(&now, &tm);
-
-    strftime(datebuf, sizeof(datebuf), "%a, %d %b %Y %H:%M:%S GMT", &tm);
-
-    return g_strdup(datebuf);
+    return g_date_time_format(now, "%a, %d %b %Y %H:%M:%S GMT");
 }
 
 static void qio_channel_websock_handshake_send_res_err(QIOChannelWebsock *ioc,