fix: alarms api return time (#5612)

apps/emqx/src/emqx_alarm.erl

@@ -159,6 +159,7 @@ format(#activated_alarm{name = Name, message = Message, activate_at = At, detail
         name => Name,
         message => Message,
         duration => (Now - At) div 1000, %% to millisecond
+        activate_at => to_rfc3339(At),
         details => Details
     };
 format(#deactivated_alarm{name = Name, message = Message, activate_at = At, details = Details,
@@ -168,11 +169,16 @@ format(#deactivated_alarm{name = Name, message = Message, activate_at = At, deta
         name => Name,
         message => Message,
         duration => DAt - At,
+        activate_at => to_rfc3339(At),
+        deactivate_at => to_rfc3339(DAt),
         details => Details
     };
 format(_) ->
     {error, unknow_alarm}.
 
+to_rfc3339(Timestamp) ->
+    list_to_binary(calendar:system_time_to_rfc3339(Timestamp div 1000, [{unit, millisecond}])).
+
 %%--------------------------------------------------------------------
 %% gen_server callbacks
 %%--------------------------------------------------------------------

apps/emqx_management/src/emqx_mgmt_api_alarms.erl

@@ -42,7 +42,9 @@ properties() ->
         {name, string, <<"Alarm name">>},
         {message, string, <<"Alarm readable information">>},
         {details, object},
-        {duration, integer, <<"Alarms duration time; UNIX time stamp">>}
+        {duration, integer, <<"Alarms duration time; UNIX time stamp, millisecond">>},
+        {activate_at, string, <<"Alarms activate time, RFC 3339">>},
+        {deactivate_at, string, <<"Nullable, alarms deactivate time, RFC 3339">>}
     ]).
 
 alarms_api() ->