diff --git a/src/emqx_protocol.erl b/src/emqx_protocol.erl
index 19a1dd838..9b9ef7f7d 100644
--- a/src/emqx_protocol.erl
+++ b/src/emqx_protocol.erl
@@ -21,6 +21,7 @@
 -export([init/2]).
 -export([info/1]).
 -export([attrs/1]).
+-export([attr/2]).
 -export([caps/1]).
 -export([stats/1]).
 -export([client_id/1]).
@@ -162,6 +163,28 @@ attrs(#pstate{zone         = Zone,
      {is_bridge, IsBridge},
      {connected_at, ConnectedAt}].
 
+attr(max_inflight, #pstate{proto_ver = ?MQTT_PROTO_V5, conn_props = ConnProps}) ->
+    get_property('Receive-Maximum', ConnProps, 65535);
+attr(max_inflight, #pstate{zone = Zone}) ->
+    emqx_zone:get_env(Zone, max_inflight, 65535);
+attr(expiry_interval, #pstate{proto_ver = ?MQTT_PROTO_V5, conn_props = ConnProps}) ->
+    get_property('Session-Expiry-Interval', ConnProps, 0);
+attr(expiry_interval, #pstate{zone = Zone, clean_start = CleanStart}) ->
+    case CleanStart of
+        true -> 0;
+        false -> emqx_zone:get_env(Zone, session_expiry_interval, 16#ffffffff)
+    end;
+attr(topic_alias_maximum, #pstate{proto_ver = ?MQTT_PROTO_V5, conn_props = ConnProps}) ->
+    get_property('Topic-Alias-Maximum', ConnProps, 0);
+attr(topic_alias_maximum, #pstate{zone = Zone}) ->
+    emqx_zone:get_env(Zone, max_topic_alias, 0);
+attr(Name, PState) ->
+    Attrs = lists:zip(record_info(fields, pstate), tl(tuple_to_list(PState))),
+    case lists:keyfind(Name, 1, Attrs) of
+        {_, Value} -> Value;
+        false -> undefined
+    end.
+
 caps(#pstate{zone = Zone}) ->
     emqx_mqtt_caps:get_caps(Zone).
 
@@ -348,8 +371,8 @@ process_packet(?CONNECT_PACKET(
                       PState3 = maybe_assign_client_id(PState2#pstate{is_super = IsSuper}),
                       emqx_logger:set_metadata_client_id(PState3#pstate.client_id),
                       %% Open session
-                      SessAttrs = lists:foldl(fun set_session_attrs/2, #{will_msg => make_will_msg(ConnPkt)}, [{max_inflight, PState3}, {expiry_interval, PState3}, {misc, PState3}]),
-                      case try_open_session(SessAttrs) of
+                      SessAttrs = #{will_msg => make_will_msg(ConnPkt)},
+                      case try_open_session(SessAttrs, PState3) of
                           {ok, SPid, SP} ->
                               PState4 = PState3#pstate{session = SPid, connected = true},
                               ok = emqx_cm:register_connection(client_id(PState4)),
@@ -673,54 +696,26 @@ maybe_assign_client_id(PState = #pstate{client_id = <<>>, ack_props = AckProps})
 maybe_assign_client_id(PState) ->
     PState.
 
-try_open_session(SessAttrs = #{zone        := _,
-                               client_id   := _,
-                               conn_pid    := _,
-                               username    := _,
-                               will_msg    := _,
-                               clean_start := _}) ->
-    case emqx_sm:open_session(SessAttrs) of
+try_open_session(SessAttrs, PState = #pstate{zone = Zone,
+                                             client_id = ClientId,
+                                             conn_pid = ConnPid,
+                                             username = Username,
+                                             clean_start = CleanStart}) ->
+    case emqx_sm:open_session(
+           maps:merge(#{zone => Zone,
+                        client_id => ClientId,
+                        conn_pid => ConnPid,
+                        username => Username,
+                        clean_start => CleanStart,
+                        max_inflight => attr(max_inflight, PState),
+                        expiry_interval => attr(expiry_interval, PState),
+                        topic_alias_maximum => attr(topic_alias_maximum, PState)},
+                      SessAttrs)) of
         {ok, SPid} ->
             {ok, SPid, false};
         Other -> Other
     end.
 
-
-set_session_attrs({max_inflight, #pstate{proto_ver = ?MQTT_PROTO_V5, conn_props = ConnProps}}, SessAttrs) ->
-    maps:put(max_inflight, get_property('Receive-Maximum', ConnProps, 65535), SessAttrs);
-
-set_session_attrs({max_inflight, #pstate{zone = Zone}}, SessAttrs) ->
-    maps:put(max_inflight, emqx_zone:get_env(Zone, max_inflight, 65535), SessAttrs);
-
-set_session_attrs({expiry_interval, #pstate{proto_ver = ?MQTT_PROTO_V5, conn_props = ConnProps}}, SessAttrs) ->
-    maps:put(expiry_interval, get_property('Session-Expiry-Interval', ConnProps, 0), SessAttrs);
-
-set_session_attrs({expiry_interval, #pstate{zone = Zone, clean_start = CleanStart}}, SessAttrs) ->
-    maps:put(expiry_interval, case CleanStart of
-                                  true -> 0;
-                                  false -> emqx_zone:get_env(Zone, session_expiry_interval, 16#ffffffff)
-                              end, SessAttrs);
-
-set_session_attrs({topic_alias_maximum, #pstate{proto_ver = ?MQTT_PROTO_V5, conn_props = ConnProps}}, SessAttrs) ->
-    maps:put(topic_alias_maximum, get_property('Topic-Alias-Maximum', ConnProps, 0), SessAttrs);
-
-set_session_attrs({topic_alias_maximum, #pstate{zone = Zone}}, SessAttrs) ->
-    maps:put(topic_alias_maximum, emqx_zone:get_env(Zone, max_topic_alias, 0), SessAttrs);
-
-set_session_attrs({misc, #pstate{zone        = Zone,
-                                 client_id   = ClientId,
-                                 conn_pid    = ConnPid,
-                                 username    = Username,
-                                 clean_start = CleanStart}}, SessAttrs) ->
-    SessAttrs#{zone        => Zone,
-               client_id   => ClientId,
-               conn_pid    => ConnPid,
-               username    => Username,
-               clean_start => CleanStart};
-
-set_session_attrs(_, SessAttrs) ->
-    SessAttrs.
-
 authenticate(Credentials, Password) ->
     case emqx_access_control:authenticate(Credentials, Password) of
         ok -> {ok, false};
@@ -978,3 +973,4 @@ reason_codes_compat(unsuback, _ReasonCodes, _ProtoVer) ->
     undefined;
 reason_codes_compat(PktType, ReasonCodes, _ProtoVer) ->
     [emqx_reason_codes:compat(PktType, RC) || RC <- ReasonCodes].
+