Support to configure keepalive backoff

etc/emq.conf

@@ -177,6 +177,9 @@ mqtt.max_packet_size = 64KB
 ## Check Websocket Protocol Header. Enum: on, off
 mqtt.websocket_protocol_header = on
 
+## The Keepalive timeout: Keepalive * backoff * 2
+mqtt.keepalive_backoff = 1.25
+
 ##--------------------------------------------------------------------
 ## MQTT Connection
 ##--------------------------------------------------------------------

priv/emq.schema

@@ -474,9 +474,16 @@ end}.
   {datatype, bytesize}
 ]}.
 
+%% @doc Keepalive backoff
+{mapping, "mqtt.keepalive_backoff", "emqttd.protocol", [
+  {default, 1.25},
+  {datatype, float}
+]}.
+
 {translation, "emqttd.protocol", fun(Conf) ->
   [{max_clientid_len, cuttlefish:conf_get("mqtt.max_clientid_len", Conf)},
-   {max_packet_size,  cuttlefish:conf_get("mqtt.max_packet_size", Conf)}]
+   {max_packet_size, cuttlefish:conf_get("mqtt.max_packet_size", Conf)},
+   {keepalive_backoff, cuttlefish:conf_get("mqtt.keepalive_backoff", Conf)}]
 end}.
 
 {mapping, "mqtt.websocket_protocol_header", "emqttd.websocket_protocol_header", [

src/emqttd_protocol.erl

@@ -42,8 +42,9 @@
 %% ws_initial_headers: Headers from first HTTP request for WebSocket Client.
 -record(proto_state, {peername, sendfun, connected = false, client_id, client_pid,
                       clean_sess, proto_ver, proto_name, username, is_superuser,
-                      will_msg, keepalive, max_clientid_len, session, stats_data,
-                      mountpoint, ws_initial_headers, connected_at}).
+                      will_msg, keepalive, keepalive_backoff, max_clientid_len,
+                      session, stats_data, mountpoint, ws_initial_headers,
+                      connected_at}).
 
 -type(proto_state() :: #proto_state{}).
 
@@ -58,6 +59,7 @@
 
 %% @doc Init protocol
 init(Peername, SendFun, Opts) ->
+    Backoff = get_value(keepalive_backoff, Opts, 1.25),
     EnableStats = get_value(client_enable_stats, Opts, false),
     MaxLen = get_value(max_clientid_len, Opts, ?MAX_CLIENTID_LEN),
     WsInitialHeaders = get_value(ws_initial_headers, Opts),
@@ -67,6 +69,7 @@ init(Peername, SendFun, Opts) ->
                  is_superuser       = false,
                  client_pid         = self(),
                  ws_initial_headers = WsInitialHeaders,
+                 keepalive_backoff  = Backoff,
                  stats_data         = #proto_stats{enable_stats = EnableStats}}.
 
 init(Conn, Peername, SendFun, Opts) ->
@@ -202,7 +205,7 @@ process(?CONNECT_PACKET(Var), State0) ->
                             %% Register the client
                             emqttd_cm:reg(client(State2)),
                             %% Start keepalive
-                            start_keepalive(KeepAlive),
+                            start_keepalive(KeepAlive, State2),
                             %% Emit Stats
                             self() ! emit_stats,
                             %% ACCEPT
@@ -411,10 +414,10 @@ send_willmsg(_Client, undefined) ->
 send_willmsg(#mqtt_client{client_id = ClientId, username = Username}, WillMsg) ->
     emqttd:publish(WillMsg#mqtt_message{from = {ClientId, Username}}).
 
-start_keepalive(0) -> ignore;
+start_keepalive(0, _State) -> ignore;
 
-start_keepalive(Sec) when Sec > 0 ->
-    self() ! {keepalive, start, round(Sec * 1.25)}.
+start_keepalive(Sec, #proto_state{keepalive_backoff = Backoff}) when Sec > 0 ->
+    self() ! {keepalive, start, round(Sec * Backoff)}.
 
 %%--------------------------------------------------------------------
 %% Validate Packets