fix(doc): Update the documentation/keepalive according to the review.

apps/emqx/src/emqx_channel.erl

@@ -1670,7 +1670,8 @@ ensure_keepalive_timer(0, Channel) -> Channel;
 ensure_keepalive_timer(disabled, Channel) -> Channel;
 ensure_keepalive_timer(Interval, Channel = #channel{clientinfo = #{zone := Zone}}) ->
     Backoff = get_mqtt_conf(Zone, keepalive_backoff),
-    Keepalive = emqx_keepalive:init(round(timer:seconds(Interval) * Backoff)),
+    RecvOct = emqx_pd:get_counter(incoming_bytes),
+    Keepalive = emqx_keepalive:init(RecvOct, round(timer:seconds(Interval) * Backoff)),
     ensure_timer(alive_timer, Channel#channel{keepalive = Keepalive}).
 
 clear_keepalive(Channel = #channel{timers = Timers}) ->

apps/emqx/src/emqx_keepalive.erl

@@ -17,6 +17,7 @@
 -module(emqx_keepalive).
 
 -export([ init/1
+        , init/2
         , info/1
         , info/2
         , check/2
@@ -37,9 +38,13 @@
 
 %% @doc Init keepalive.
 -spec(init(Interval :: non_neg_integer()) -> keepalive()).
-init(Interval) when Interval > 0 ->
+init(Interval) -> init(0, Interval).
+
+%% @doc Init keepalive.
+-spec(init(StatVal :: non_neg_integer(), Interval :: non_neg_integer()) -> keepalive()).
+init(StatVal, Interval) when Interval > 0 ->
     #keepalive{interval = Interval,
-               statval  = emqx_pd:get_counter(incoming_bytes),
+               statval  = StatVal,
                repeat   = 0}.
 
 %% @doc Get Info of the keepalive.

apps/emqx/src/emqx_schema.erl

@@ -157,7 +157,7 @@ roots(low) ->
        sc(ref("force_gc"),
           #{ desc =>
 """Force the MQTT connection process garbage collection after
-this number of messages or bytes passed through."""
+this number of messages or bytes have passed through."""
           })}
    , {"conn_congestion",
        sc(ref("conn_congestion"),
@@ -334,17 +334,17 @@ message within this interval."""
     , {"shared_subscription",
        sc(boolean(),
           #{ default => true,
-             desc => "Support MQTT Shared Subscriptions"
+             desc => "Support MQTT Shared Subscriptions."
            })}
     , {"ignore_loop_deliver",
        sc(boolean(),
           #{ default => false,
-             desc => "Ignore loop delivery of messages for mqtt v3.1.1"
+             desc => "Ignore loop delivery of messages for mqtt v3.1.1."
            })}
     , {"strict_mode",
        sc(boolean(),
           #{default => false,
-            desc => "Parse the MQTT frame in strict mode"
+            desc => "Parse the MQTT frame in strict mode."
            })
       }
     , {"response_information",
@@ -358,7 +358,10 @@ This feature is disabled if is set to \"\"."""
     , {"server_keepalive",
        sc(hoconsc:union([integer(), disabled]),
           #{ default => disabled,
-             desc => "Server Keep Alive of MQTT 5.0"
+             desc =>
+"""Server Keep Alive of MQTT 5.0.
+If the Server returns a Server Keep Alive on the CONNACK packet,
+the Client MUST use that value instead of the value it sent as the Keep Alive."""
            })
       }
     , {"keepalive_backoff",
@@ -378,7 +381,7 @@ after idling for 'Keepalive * backoff * 2'."""
     , {"upgrade_qos",
        sc(boolean(),
           #{ default => false,
-             desc => "Force to upgrade QoS according to subscription."
+             desc => "Force upgrade of QoS level according to subscription."
            })
       }
     , {"max_inflight",
@@ -427,9 +430,9 @@ or inflight window is full."""
 There's no priority table by default, hence all messages are treated equal.<br>
 Priority number [1-255]<br>
 
-**NOTE**: Comma and equal signs are not allowed for priority topic names<br>
+**NOTE**: Comma and equal signs are not allowed for priority topic names.<br>
 **NOTE**: Messages for topics not in the priority table are treated as
-either highest or lowest priority depending on the configured value for mqtt.mqueue_default_priority
+either highest or lowest priority depending on the configured value for mqtt.mqueue_default_priority.
 <br><br>
 **Examples**:
 To configure \"topic/1\" > \"topic/2\":
@@ -439,7 +442,7 @@ mqueue_priorities: {\"topic/1\": 10, \"topic/2\": 8}"""
     , {"mqueue_default_priority",
        sc(hoconsc:enum([highest, lowest]),
           #{ default => lowest,
-             desc => "Default to highest priority for topics not matching priority table"
+             desc => "Default to highest priority for topics not matching priority table."
            })
       }
     , {"mqueue_store_qos0",
@@ -451,7 +454,7 @@ mqueue_priorities: {\"topic/1\": 10, \"topic/2\": 8}"""
     , {"use_username_as_clientid",
        sc(boolean(),
           #{ default => false,
-             desc => "Replace client id with the username"
+             desc => "Replace client id with the username."
            })
       }
     , {"peer_cert_as_username",
@@ -587,12 +590,12 @@ fields("force_gc") ->
     , {"count",
        sc(range(0, inf),
           #{ default => 16000,
-             desc =>  "GC the process after this many received messages"
+             desc =>  "GC the process after this many received messages."
            })}
     , {"bytes",
        sc(bytesize(),
           #{ default => "16MB",
-             desc => "GC the process after how much bytes passed through"
+             desc => "GC the process after specified number of bytes have passed through."
            })}
     ];
 

apps/emqx/test/emqx_keepalive_SUITE.erl

@@ -39,4 +39,3 @@ t_check(_) ->
     ?assertEqual(1, emqx_keepalive:info(statval, Keepalive2)),
     ?assertEqual(1, emqx_keepalive:info(repeat, Keepalive2)),
     ?assertEqual({error, timeout}, emqx_keepalive:check(1, Keepalive2)).
-