Tweak map-valued decode

Use the same [MsgName | Avps] representation as for the list decode, but
with Avps a map instead of a AVP name/values list. As a result, don't
set the message/AVP name on an additional key in the map, which felt a
bit odd. Messages are [MsgName :: atom() | map()], Grouped AVPs are just
map().

Fix at least one problem in the traffic suite along the way: with
decode_format false, the own decode in to_map/2 didn't know whether or
not to decode strings, resulting on some failures.

6 files changed, 193 insertions, 237 deletions

diff --git a/lib/diameter/doc/src/diameter.xml b/lib/diameter/doc/src/diameter.xml
index a7f001e096..43cb3a538c 100644
--- a/lib/diameter/doc/src/diameter.xml
+++ b/lib/diameter/doc/src/diameter.xml
@@ -539,7 +539,7 @@ that matches no peer.</p>
 <p>
 The <c>host</c> and <c>realm</c> filters cause the Destination-Host
 and Destination-Realm AVPs to be extracted from the
-outgoing request, assuming it to be a record-, list- or map-valued
+outgoing request, assuming it to be a record- or list-valued
 <c>&codec_message;</c>, and assuming at most one of each AVP.
 If this is not the case then the <c>{host|realm, &dict_DiameterIdentity;}</c>
 filters must be used to achieve the desired result.
@@ -802,10 +802,16 @@ be matched by corresponding &capability; configuration, of
 <c>{decode_format, record | list | map | false}</c></tag>
 <item>
 <p>
-The type of decoded messages and grouped AVPs in the <c>msg</c> field
+The format of decoded messages and grouped AVPs in the <c>msg</c> field
 of diameter_packet records and <c>value</c> field of diameter_avp
 records respectively.
-If <c>false</c> then the fields are set this value.
+If <c>record</c> then a record whose definition is generated from the
+dictionary file in question.
+If <c>list</c> or <c>map</c> then a <c>[Name | Avps]</c> pair where
+<c>Avps</c> is either a list of AVP name/values pairs or a map keyed on
+AVP names respectively.
+If <c>false</c> then the representation is omitted and <c>msg</c> and
+<c>value</c> fields are set to <c>false</c>.
 See also &codec_message;.</p>
 
 <p>
diff --git a/lib/diameter/doc/src/diameter_codec.xml b/lib/diameter/doc/src/diameter_codec.xml
index 4df8e788b7..0846334d23 100644
--- a/lib/diameter/doc/src/diameter_codec.xml
+++ b/lib/diameter/doc/src/diameter_codec.xml
@@ -230,7 +230,8 @@ header.</p>
 </item>
 
 <tag>
-<marker id="message"/><c>message() = record() | list() | map()</c></tag>
+<marker id="message"/><c>message() = record()
+                                   | maybe_improper_list()</c></tag>
 <item>
 <p>
 The representation of a Diameter message as passed to
@@ -240,9 +241,8 @@ a message as defined in a dictionary file is encoded as a record with
 one field for each component AVP.
 Equivalently, a message can also be encoded as a list whose head is
 the atom-valued message name (as specified in the relevant dictionary
-file) and whose tail is a list of <c>{AvpName, AvpValues}</c> pairs,
-or as a map with values keyed on AVP names and the message name in key
-<c>:name</c>.
+file) and whose tail is either a list of AVP name/values
+pairs or a map with values keyed on AVP names.
 The format at decode is determined by &mod_service_opt;
 <c>decode_format</c>.
 Any of the formats is accepted at encode.</p>
diff --git a/lib/diameter/src/base/diameter_codec.erl b/lib/diameter/src/base/diameter_codec.erl
index 275e80b9bb..9b21bf4141 100644
--- a/lib/diameter/src/base/diameter_codec.erl
+++ b/lib/diameter/src/base/diameter_codec.erl
@@ -275,9 +275,6 @@ rec2msg(_, [Name|_])
   when is_atom(Name) ->
     Name;
 
-rec2msg(_, #{':name' := Name}) ->
-    Name;
-
 rec2msg(Mod, Rec) ->
     Mod:rec2msg(element(1, Rec)).
 
@@ -383,7 +380,9 @@ decode_avps(MsgName, Mod, AppMod, Opts, Pkt, Avps) ->  %% ... or not
                         errors = Errors,
                         avps = As}.
 
-reformat(MsgName, Avps, #{decode_format := list}) ->
+reformat(MsgName, Avps, #{decode_format := T})
+  when T == map;
+       T == list ->
     [MsgName | Avps];
 
 reformat(_, Msg, _) ->
diff --git a/lib/diameter/src/base/diameter_gen.erl b/lib/diameter/src/base/diameter_gen.erl
index 78d8bd2fa3..597ec143a8 100644
--- a/lib/diameter/src/base/diameter_gen.erl
+++ b/lib/diameter/src/base/diameter_gen.erl
@@ -186,7 +186,7 @@ decode_avps(Name, Recs, #{module := Mod, decode_format := Fmt} = Opts) ->
     %% AM counts the number of top-level AVPs, which missing/4 then
     %% uses when adding 5005 errors.
     Arities = Mod:avp_arity(Name),
-    {reformat(Rec, Arities, Mod, Fmt),
+    {reformat(Name, Rec, Arities, Mod, Fmt),
      Avps,
      Failed ++ missing(Arities, Opts, Mod, AM)}.
 
@@ -752,8 +752,8 @@ newrec(_, _, false = No) ->
 newrec(Mod, Name, record) ->
     newrec(Mod, Name);
 
-newrec(_, Name, _) ->
-    #{':name' => Name}.
+newrec(_, _, _) ->
+    #{}.
 
 %% newrec/2
 
@@ -762,15 +762,14 @@ newrec(Mod, Name) ->
 
 %% reformat/4
 
-reformat(Map, Arities, _Mod, list) ->
+reformat(_, Map, Arities, _Mod, list) ->
     [{F,V} || {F,_} <- Arities, #{F := V} <- [Map]];
 
-reformat(Map, Arities, Mod, record_from_map) ->
-    #{':name' := Name} = Map,
+reformat(Name, Map, Arities, Mod, record_from_map) ->
     RecName = Mod:name2rec(Name),
     list_to_tuple([RecName | [maps:get(F, Map, def(A)) || {F,A} <- Arities]]);
 
-reformat(Rec, _, _, _) ->
+reformat(_, Rec, _, _, _) ->
     Rec.
 
 %% def/1
diff --git a/lib/diameter/src/base/diameter_traffic.erl b/lib/diameter/src/base/diameter_traffic.erl
index f684f60cb7..e9c422d6ab 100644
--- a/lib/diameter/src/base/diameter_traffic.erl
+++ b/lib/diameter/src/base/diameter_traffic.erl
@@ -621,16 +621,10 @@ is_answer_message(#diameter_packet{msg = Msg}, Dict0) ->
 is_answer_message([#diameter_header{is_request = R, is_error = E} | _], _) ->
     E andalso not R;
 
-%% Message sent as a tagged avp/value list.
+%% Message sent as a map or tagged avp/value list.
 is_answer_message([Name | _], _) ->
     Name == 'answer-message';
 
-%% Message sent as a map.
-is_answer_message(Map, _)
-  when is_map(Map) ->
-    #{':name' := Name} = Map,
-    Name == 'answer-message';
-
 %% Message sent as a record.
 is_answer_message(Rec, Dict) ->
     try
@@ -875,15 +869,13 @@ reset(Msg, [RC | Avps], Dict) ->
 
 %% set/3
 
-%% Reply as name and tuple list ...
+%% Reply as name/values list ...
+set([Name|As], Avps, _)
+  when is_map(As) ->
+    [Name | maps:merge(As, maps:from_list(Avps))];
 set([_|_] = Ans, Avps, _) ->
     Ans ++ Avps;  %% Values nearer tail take precedence.
 
-%% ... a map ...
-set(Ans, Avps, _)
-  when is_map(Ans) ->
-    maps:merge(Ans, maps:from_list(Avps));
-
 %% ... or record.
 set(Rec, Avps, Dict) ->
     Dict:'#set-'(Avps, Rec).
@@ -902,9 +894,6 @@ rc([MsgName | _], RC, Dict) ->
         _     -> []
     end;
 
-rc(#{':name' := Name}, RC, Dict) ->
-    rc([Name], RC, Dict);
-
 rc(Rec, RC, Dict) ->
     rc([Dict:rec2msg(element(1, Rec))], RC, Dict).
 
@@ -937,10 +926,6 @@ failed(Msg, FailedAvp, Dict) ->
 msg2rec([MsgName | _], Dict) ->
     Dict:msg2rec(MsgName);
 
-%% ... map ...
-msg2rec(#{':name' := MsgName}, Dict) ->
-    Dict:msg2rec(MsgName);
-
 %% ... or record.
 msg2rec(Rec, _) ->
     element(1, Rec).
@@ -949,12 +934,11 @@ msg2rec(Rec, _) ->
 
 %% Message as name/values list ...
 values([_ | Avps], F, _) ->
-    proplists:get_value(F, Avps, []);
-
-%% ... map ...
-values(Msg, F, _)
-  when is_map(Msg) ->
-    maps:get(F, Msg, []);
+    if is_map(Avps) ->
+            maps:get(F, Avps, []);
+       is_list(Avps) ->
+            proplists:get_value(F, Avps, [])
+    end;
 
 %% ... or record.
 values(Rec, F, Dict) ->
@@ -1906,23 +1890,13 @@ get_avp(Dict, Name, [#diameter_header{} | Avps]) ->
 
 %% Message as name/values list ...
 get_avp(_, Name, [_MsgName | Avps]) ->
-    case lists:keyfind(Name, 1, Avps) of
+    case find(Name, Avps) of
         {_, V} ->
             #diameter_avp{name = Name, value = V};
         _ ->
             undefined
     end;
 
-%% ... map ...
-get_avp(_, Name, Map)
-  when is_map(Map) ->
-    case maps:find(Name, Map) of
-        {ok, V} ->
-            #diameter_avp{name = Name, value = V};
-        error ->
-            undefined
-    end;
-
 %% ... or record (but not necessarily).
 get_avp(Dict, Name, Rec) ->
     try
@@ -1932,6 +1906,16 @@ get_avp(Dict, Name, Rec) ->
             undefined
     end.
 
+%% find/2
+
+find(Key, Map)
+  when is_map(Map) ->
+    maps:find(Key, Map);
+
+find(Key, List)
+  when is_list(List) ->
+    lists:keyfind(Key, 1, List).
+
 %% get_avp_value/3
 
 get_avp_value(Dict, Name, Msg) ->
diff --git a/lib/diameter/test/diameter_traffic_SUITE.erl b/lib/diameter/test/diameter_traffic_SUITE.erl
index 100a4eebc9..fae9f86c38 100644
--- a/lib/diameter/test/diameter_traffic_SUITE.erl
+++ b/lib/diameter/test/diameter_traffic_SUITE.erl
@@ -99,14 +99,14 @@
          stop/1]).
 
 %% diameter callbacks
--export([peer_up/3,
-         peer_down/3,
-         pick_peer/6, pick_peer/7,
-         prepare_request/5, prepare_request/6,
-         prepare_retransmit/5,
-         handle_answer/6, handle_answer/7,
-         handle_error/6,
-         handle_request/3]).
+-export([peer_up/4,
+         peer_down/4,
+         pick_peer/7, pick_peer/8,
+         prepare_request/6, prepare_request/7,
+         prepare_retransmit/6,
+         handle_answer/7, handle_answer/8,
+         handle_error/7,
+         handle_request/4]).
 
 %% diameter_{tcp,sctp} callbacks
 -export([message/3]).
@@ -182,19 +182,17 @@
 
 %% A common match when receiving answers in a client.
 -define(answer_message(SessionId, ResultCode),
-        #{':name' := 'answer-message',
-          'Session-Id' := SessionId,
-          'Origin-Host' := _,
-          'Origin-Realm' := _,
-          'Result-Code' := ResultCode}).
+        ['answer-message' | #{'Session-Id' := SessionId,
+                              'Origin-Host' := _,
+                              'Origin-Realm' := _,
+                              'Result-Code' := ResultCode}]).
 -define(answer_message(ResultCode),
-        #{':name' := 'answer-message',
-          'Origin-Host' := _,
-          'Origin-Realm' := _,
-          'Result-Code' := ResultCode}).
+        ['answer-message' | #{'Origin-Host' := _,
+                              'Origin-Realm' := _,
+                              'Result-Code' := ResultCode}]).
 
 %% Config for diameter:start_service/2.
--define(SERVICE(Name, Decode),
+-define(SERVICE(Name, Grp),
         [{'Origin-Host', Name ++ "." ++ ?REALM},
          {'Origin-Realm', ?REALM},
          {'Host-IP-Address', [?ADDR]},
@@ -203,10 +201,10 @@
          {'Auth-Application-Id', [0]},  %% common messages
          {'Acct-Application-Id', [3]},  %% base accounting
          {restrict_connections, false},
-         {string_decode, Decode},
+         {string_decode, Grp#group.strings},
          {incoming_maxlen, 1 bsl 21}
          | [{application, [{dictionary, D},
-                           {module, ?MODULE},
+                           {module, [?MODULE, Grp]},
                            {answer_errors, callback}]}
             || D <- [diameter_gen_base_rfc3588,
                      diameter_gen_base_accounting,
@@ -446,15 +444,15 @@ start(_Config) ->
     ok = diameter:start().
 
 start_services(Config) ->
-    #group{strings = S,
-           client_service = CN,
+    #group{client_service = CN,
            server_service = SN,
            server_decoding = SD}
+        = Grp
         = group(Config),
     ok = diameter:start_service(SN, [{decode_format, SD}
-                                     | ?SERVICE(SN, S)]),
+                                     | ?SERVICE(SN, Grp)]),
     ok = diameter:start_service(CN, [{sequence, ?CLIENT_MASK}
-                                     | ?SERVICE(CN, S)]).
+                                     | ?SERVICE(CN, Grp)]).
 
 add_transports(Config) ->
     #group{transport = T,
@@ -484,8 +482,6 @@ add_transports(Config) ->
              R <- ?RFCS,
              R /= rfc4005 orelse have_nas(),
              Id <- [{D,E}]],
-    %% The server uses the client's Origin-State-Id to decide how to
-    %% answer.
     ?util:write_priv(Config, "transport", [LRef | Cs]).
 
 server_apps() ->
@@ -567,9 +563,8 @@ send_ok(Config) ->
     Req = ['ACR', {'Accounting-Record-Type', ?EVENT_RECORD},
                   {'Accounting-Record-Number', 1}],
 
-    #{':name' := 'ACA',
-      'Result-Code' := ?SUCCESS,
-      'Session-Id' := _}
+    ['ACA' | #{'Result-Code' := ?SUCCESS,
+               'Session-Id' := _}]
         = call(Config, Req).
 
 %% Send an accounting ACR that the server answers badly to.
@@ -585,9 +580,8 @@ send_eval(Config) ->
     Req = ['ACR', {'Accounting-Record-Type', ?EVENT_RECORD},
                   {'Accounting-Record-Number', 3}],
 
-    #{':name' := 'ACA',
-      'Result-Code' := ?SUCCESS,
-      'Session-Id' := _}
+    ['ACA' | #{'Result-Code' := ?SUCCESS,
+               'Session-Id' := _}]
         = call(Config, Req).
 
 %% Send an accounting ACR that the server tries to answer with an
@@ -613,8 +607,7 @@ send_protocol_error(Config) ->
 send_experimental_result(Config) ->
     Req = ['ACR', {'Accounting-Record-Type', ?EVENT_RECORD},
                   {'Accounting-Record-Number', 5}],
-    #{':name' := 'ACA',
-      'Session-Id' := _}
+    ['ACA' | #{'Session-Id' := _}]
         = call(Config, Req).
 
 %% Send an ASR with an arbitrary non-mandatory AVP and expect success
@@ -622,11 +615,10 @@ send_experimental_result(Config) ->
 send_arbitrary(Config) ->
     Req = ['ASR', {'AVP', [#diameter_avp{name = 'Product-Name',
                                          value = "XXX"}]}],
-    #{':name' := 'ASA',
-      'Session-Id' := _,
-      'Result-Code' := ?SUCCESS,
-      'AVP' := [#diameter_avp{name = 'Product-Name',
-                              value = V}]}
+    ['ASA' | #{'Session-Id' := _,
+               'Result-Code' := ?SUCCESS,
+               'AVP' := [#diameter_avp{name = 'Product-Name',
+                                       value = V}]}]
         = call(Config, Req),
     "XXX" = string(V, Config).
 
@@ -635,12 +627,11 @@ send_unknown(Config) ->
     Req = ['ASR', {'AVP', [#diameter_avp{code = 999,
                                          is_mandatory = false,
                                          data = <<17>>}]}],
-    #{':name' := 'ASA',
-      'Session-Id' := _,
-      'Result-Code' := ?SUCCESS,
-      'AVP' := [#diameter_avp{code = 999,
-                              is_mandatory = false,
-                              data = <<17>>}]}
+    ['ASA' | #{'Session-Id' := _,
+               'Result-Code' := ?SUCCESS,
+               'AVP' := [#diameter_avp{code = 999,
+                                       is_mandatory = false,
+                                       data = <<17>>}]}]
         = call(Config, Req).
 
 %% Ditto, and point the AVP length past the end of the message. Expect
@@ -652,10 +643,9 @@ send_unknown_short(Config, M, RC) ->
     Req = ['ASR', {'AVP', [#diameter_avp{code = 999,
                                          is_mandatory = M,
                                          data = <<17>>}]}],
-    #{':name' := 'ASA',
-      'Session-Id' := _,
-      'Result-Code' := RC,
-      'Failed-AVP' := Avps}
+    ['ASA' | #{'Session-Id' := _,
+               'Result-Code' := RC,
+               'Failed-AVP' := Avps}]
         = call(Config, Req),
     [[#diameter_avp{code = 999,
                     is_mandatory = M,
@@ -667,10 +657,9 @@ send_unknown_mandatory(Config) ->
     Req = ['ASR', {'AVP', [#diameter_avp{code = 999,
                                          is_mandatory = true,
                                          data = <<17>>}]}],
-    #{':name' := 'ASA',
-      'Session-Id' := _,
-      'Result-Code' := ?AVP_UNSUPPORTED,
-      'Failed-AVP' := Avps}
+    ['ASA' | #{'Session-Id' := _,
+               'Result-Code' := ?AVP_UNSUPPORTED,
+               'Failed-AVP' := Avps}]
         = call(Config, Req),
     [[#diameter_avp{code = 999,
                     is_mandatory = true,
@@ -688,10 +677,9 @@ send_unexpected_mandatory_decode(Config) ->
     Req = ['ASR', {'AVP', [#diameter_avp{code = 27,  %% Session-Timeout
                                          is_mandatory = true,
                                          data = <<12:32>>}]}],
-    #{':name' := 'ASA',
-      'Session-Id' := _,
-      'Result-Code' := ?AVP_UNSUPPORTED,
-      'Failed-AVP' := Avps}
+    ['ASA' | #{'Session-Id' := _,
+               'Result-Code' := ?AVP_UNSUPPORTED,
+               'Failed-AVP' := Avps}]
         = call(Config, Req),
     [[#diameter_avp{code = 27,
                     is_mandatory = true,
@@ -707,10 +695,9 @@ send_unexpected_mandatory_decode(Config) ->
 send_grouped_error(Config) ->
     Req = ['ASR', {'Proxy-Info', [[{'Proxy-Host', "abcd"},
                                    {'Proxy-State', ""}]]}],
-    #{':name' := 'ASA',
-      'Session-Id' := _,
-      'Result-Code' := ?INVALID_AVP_LENGTH,
-      'Failed-AVP' := Avps}
+    ['ASA' | #{'Session-Id' := _,
+               'Result-Code' := ?INVALID_AVP_LENGTH,
+               'Failed-AVP' := Avps}]
         = call(Config, Req),
     [[#diameter_avp{name = 'Proxy-Info', value = V}]]
         = failed_avps(Avps, Config),
@@ -743,9 +730,8 @@ send_error_bit(Config) ->
 %% Send a bad version and check that we get 5011.
 send_unsupported_version(Config) ->
     Req = ['STR', {'Termination-Cause', ?LOGOUT}],
-    #{':name' := 'STA',
-      'Session-Id' := _,
-      'Result-Code' := ?UNSUPPORTED_VERSION}
+    ['STA' | #{'Session-Id' := _,
+               'Result-Code' := ?UNSUPPORTED_VERSION}]
         = call(Config, Req).
 
 %% Send a request containing an AVP length > data size.
@@ -765,12 +751,11 @@ send_zero_avp_length(Config) ->
 send_invalid_avp_length(Config) ->
     Req = ['STR', {'Termination-Cause', ?LOGOUT}],
 
-    #{':name' := 'STA',
-      'Session-Id' := _,
-      'Result-Code' := ?INVALID_AVP_LENGTH,
-      'Origin-Host' := _,
-      'Origin-Realm' := _,
-      'Failed-AVP' := Avps}
+    ['STA' | #{'Session-Id' := _,
+               'Result-Code' := ?INVALID_AVP_LENGTH,
+               'Origin-Host' := _,
+               'Origin-Realm' := _,
+               'Failed-AVP' := Avps}]
         = call(Config, Req),
     [[_]] = failed_avps(Avps, Config).
 
@@ -787,18 +772,16 @@ send_invalid_reject(Config) ->
 send_unexpected_mandatory(Config) ->
     Req = ['STR', {'Termination-Cause', ?LOGOUT}],
 
-    #{':name' := 'STA',
-      'Session-Id' := _,
-      'Result-Code' := ?AVP_UNSUPPORTED}
+    ['STA' | #{'Session-Id' := _,
+               'Result-Code' := ?AVP_UNSUPPORTED}]
         = call(Config, Req).
 
 %% Send something long that will be fragmented by TCP.
 send_long(Config) ->
     Req = ['STR', {'Termination-Cause', ?LOGOUT},
                   {'User-Name', [binary:copy(<<$X>>, 1 bsl 20)]}],
-    #{':name' := 'STA',
-      'Session-Id' := _,
-      'Result-Code' := ?SUCCESS}
+    ['STA' | #{'Session-Id' := _,
+               'Result-Code' := ?SUCCESS}]
         = call(Config, Req).
 
 %% Send something longer than the configure incoming_maxlen.
@@ -841,9 +824,8 @@ send_any_2(Config) ->
 send_all_1(Config) ->
     Req = ['STR', {'Termination-Cause', ?LOGOUT}],
     Realm = lists:foldr(fun(C,A) -> [C,A] end, [], ?REALM),
-    #{':name' := 'STA',
-      'Session-Id' := _,
-      'Result-Code' := ?SUCCESS}
+    ['STA' | #{'Session-Id' := _,
+               'Result-Code' := ?SUCCESS}]
         = call(Config, Req, [{filter, {all, [{host, any},
                                              {realm, Realm}]}}]).
 send_all_2(Config) ->
@@ -872,9 +854,8 @@ send_detach(Config) ->
     Req = ['STR', {'Termination-Cause', ?LOGOUT}],
     Ref = make_ref(),
     ok = call(Config, Req, [{extra, [{self(), Ref}]}, detach]),
-    #{':name' := 'STA',
-      'Session-Id' := _,
-      'Result-Code' := ?SUCCESS}
+    ['STA' | #{'Session-Id' := _,
+               'Result-Code' := ?SUCCESS}]
         = receive {Ref, T} -> T end.
 
 %% Send a request which can't be encoded and expect {error, encode}.
@@ -887,15 +868,13 @@ send_destination_1(Config) ->
         = group(Config),
     Req = ['STR', {'Termination-Cause', ?LOGOUT},
                   {'Destination-Host', [?HOST(SN, ?REALM)]}],
-    #{':name' := 'STA',
-      'Session-Id' := _,
-      'Result-Code' := ?SUCCESS}
+    ['STA' | #{'Session-Id' := _,
+               'Result-Code' := ?SUCCESS}]
         = call(Config, Req, [{filter, {all, [host, realm]}}]).
 send_destination_2(Config) ->
     Req = ['STR', {'Termination-Cause', ?LOGOUT}],
-    #{':name' := 'STA',
-      'Session-Id' := _,
-      'Result-Code' := ?SUCCESS}
+    ['STA' | #{'Session-Id' := _,
+               'Result-Code' := ?SUCCESS}]
         = call(Config, Req, [{filter, {all, [host, realm]}}]).
 
 %% Send with filtering on and expect failure when specifying an
@@ -959,9 +938,8 @@ send_bad_filter(Config, F) ->
 %% Specify multiple filter options and expect them be conjunctive.
 send_multiple_filters_1(Config) ->
     Fun = fun(#diameter_caps{}) -> true end,
-    #{':name' := 'STA',
-      'Session-Id' := _,
-      'Result-Code' := ?SUCCESS}
+    ['STA' | #{'Session-Id' := _,
+               'Result-Code' := ?SUCCESS}]
         = send_multiple_filters(Config, [host, {eval, Fun}]).
 send_multiple_filters_2(Config) ->
     E = {erlang, is_tuple, []},
@@ -972,9 +950,8 @@ send_multiple_filters_3(Config) ->
     E2 = {erlang, is_tuple, []},
     E3 = {erlang, is_record, [diameter_caps]},
     E4 = [{erlang, is_record, []}, diameter_caps],
-    #{':name' := 'STA',
-      'Session-Id' := _,
-      'Result-Code' := ?SUCCESS}
+    ['STA' | #{'Session-Id' := _,
+               'Result-Code' := ?SUCCESS}]
         = send_multiple_filters(Config, [{eval, E} || E <- [E1,E2,E3,E4]]).
 
 send_multiple_filters(Config, Fs) ->
@@ -985,9 +962,8 @@ send_multiple_filters(Config, Fs) ->
 %% only the return value from the prepare_request callback being
 %% significant.
 send_anything(Config) ->
-    #{':name' := 'STA',
-      'Session-Id' := _,
-      'Result-Code' := ?SUCCESS}
+    ['STA' | #{'Session-Id' := _,
+               'Result-Code' := ?SUCCESS}]
         = call(Config, anything).
 
 %% ===========================================================================
@@ -1037,12 +1013,11 @@ call(Config, Req, Opts) ->
     #group{encoding = Enc,
            client_service = CN,
            client_dict = Dict0}
-        = Group
         = group(Config),
     diameter:call(CN,
                   dict(Req, Dict0),
                   msg(Req, Enc, Dict0),
-                  [{extra, [{Name, Group}, diameter_lib:now()]} | Opts]).
+                  [{extra, [Name, diameter_lib:now()]} | Opts]).
 
 origin({D,E}) ->
     4*decode(D) + encode(E);
@@ -1082,32 +1057,37 @@ msg([H|_] = Msg, record = E, diameter_gen_base_rfc6733)
 msg([H|T], record, Dict) ->
     Dict:'#new-'(Dict:msg2rec(H), T);
 
-msg([H|T], map, _) ->
-    Map = maps:from_list(T),
-    Map#{':name' => H};
+msg([H|As], map, _)
+  when is_list(As) ->
+    [H | maps:from_list(As)];
 
 msg(Msg, _, _) ->
     Msg.
 
-to_map(map, #diameter_packet{msg = Msg})
-  when is_map(Msg) ->
+to_map(#diameter_packet{msg = [_MsgName | Avps] = Msg},
+       #group{server_decoding = map})
+  when is_map(Avps) ->
     Msg;
 
-to_map(list, #diameter_packet{msg = [MsgName | Avps]}) ->
-    maps:put(':name', MsgName, maps:from_list(Avps));
+to_map(#diameter_packet{msg = [MsgName | Avps]},
+       #group{server_decoding = list}) ->
+    [MsgName | maps:from_list(Avps)];
 
-to_map(record, #diameter_packet{header = H, msg = Rec}) ->
+to_map(#diameter_packet{header = H, msg = Rec},
+       #group{server_decoding = record}) ->
     rec_to_map(Rec, dict(H));
 
 %% No record decode: do it ourselves.
-to_map(false, #diameter_packet{header = H,
-                               msg = false,
-                               bin = Bin}) ->
+to_map(#diameter_packet{header = H,
+                        msg = false,
+                        bin = Bin},
+      #group{server_decoding = false,
+             strings = B}) ->
     Opts = #{decode_format => map,
-             string_decode => false,
+             string_decode => B,
              strict_mbit => true,
              rfc => 6733},
-    #diameter_packet{msg = Msg}
+    #diameter_packet{msg = [_MsgName | _Map] = Msg}
         = diameter_codec:decode(dict(H), Opts, Bin),
     Msg.
 
@@ -1123,11 +1103,9 @@ dict(#diameter_header{application_id = Id,
 
 rec_to_map(Rec, Dict) ->
     [R | Vs] = Dict:'#get-'(Rec),
-    maps:put(':name',
-             Dict:rec2msg(R),
-             maps:from_list([T || {_,V} = T <- Vs,
-                                  V /= undefined,
-                                  V /= []])).
+    [Dict:rec2msg(R) | maps:from_list([T || {_,V} = T <- Vs,
+                                            V /= undefined,
+                                            V /= []])].
 
 appdict(rfc4005) ->
     nas4005;
@@ -1166,12 +1144,12 @@ acct(diameter_gen_base_rfc6733) ->
 
 %% Set only values that aren't already.
 
-set(_, [H|T], Vs) ->
-    [H | Vs ++ T];
-
-set(_, Map, Vs)
-  when is_map(Map) ->
-    maps:merge(maps:from_list(Vs), Map);
+set(_, [N | As], Vs) ->
+    [N | if is_map(As) ->
+                 maps:merge(maps:from_list(Vs), As);
+            is_list(As) ->
+                 Vs ++ As
+         end];
 
 set(#group{client_dict = Dict0} = _Group, Rec, Vs) ->
     Dict = dict(Rec, Dict0),
@@ -1192,26 +1170,26 @@ reset(_, _, _, Rec) ->
 %% ===========================================================================
 %% diameter callbacks
 
-%% peer_up/3
+%% peer_up/4
 
-peer_up(_SvcName, _Peer, State) ->
+peer_up(_SvcName, _Peer, State, _Group) ->
     State.
 
 %% peer_down/3
 
-peer_down(_SvcName, _Peer, State) ->
+peer_down(_SvcName, _Peer, State, _Group) ->
     State.
 
-%% pick_peer/6-7
+%% pick_peer/7-8
 
-pick_peer(Peers, _, [$C|_], _State, {Name, Group}, _)
+pick_peer(Peers, _, [$C|_], _State, Group, Name, _)
   when Name /= send_detach ->
     find(Group, Peers).
 
-pick_peer(_Peers, _, [$C|_], _State, {send_nopeer, _}, _, ?EXTRA) ->
+pick_peer(_Peers, _, [$C|_], _State, _Group, send_nopeer, _, ?EXTRA) ->
     false;
 
-pick_peer(Peers, _, [$C|_], _State, {send_detach, Group}, _, {_,_}) ->
+pick_peer(Peers, _, [$C|_], _State, Group, send_detach, _, {_,_}) ->
     find(Group, Peers).
 
 find(#group{encoding = E,
@@ -1227,15 +1205,15 @@ id(Id, {Pid, _Caps}, SvcName) ->
         = diameter:service_info(SvcName, Pid),
     lists:member({id, Id}, Opts).
 
-%% prepare_request/5-6
+%% prepare_request/6-7
 
-prepare_request(_Pkt, [$C|_], {_Ref, _Caps}, {send_discard, _}, _) ->
+prepare_request(_Pkt, [$C|_], {_Ref, _Caps}, _, send_discard, _) ->
     {discard, unprepared};
 
-prepare_request(Pkt, [$C|_], {_Ref, Caps}, {Name, Group}, _) ->
+prepare_request(Pkt, [$C|_], {_Ref, Caps}, Group, Name, _) ->
     {send, prepare(Pkt, Caps, Name, Group)}.
 
-prepare_request(Pkt, [$C|_], {_Ref, Caps}, {send_detach, Group}, _, _) ->
+prepare_request(Pkt, [$C|_], {_Ref, Caps}, Group, send_detach, _, _) ->
     {eval_packet, {send, prepare(Pkt, Caps, Group)}, [fun log/2, detach]}.
 
 log(#diameter_packet{bin = Bin} = P, T)
@@ -1446,12 +1424,12 @@ set(N, #diameter_packet{msg = Req}, Caps, Group)
 
 %% name/1
 
+name([H|#{}]) ->
+    {map, H};
+
 name([H|_]) ->
     {list, H};
 
-name(#{} = Map) ->
-    {map, maps:get(':name', Map)};
-
 name(Rec) ->
     try
         {record, element(1, Rec)}
@@ -1460,17 +1438,17 @@ name(Rec) ->
             false
     end.
 
-%% prepare_retransmit/5
+%% prepare_retransmit/6
 
-prepare_retransmit(_Pkt, false, _Peer, _Name, _Group) ->
+prepare_retransmit(_Pkt, false, _Peer, _Group, _Name, _) ->
     discard.
 
-%% handle_answer/6-7
+%% handle_answer/7-8
 
-handle_answer(Pkt, Req, [$C|_], Peer, {Name, Group}, _) ->
+handle_answer(Pkt, Req, [$C|_], Peer, Group, Name, _) ->
     answer(Pkt, Req, Peer, Name, Group).
 
-handle_answer(Pkt, Req, [$C|_], Peer, {send_detach = Name, Group}, _, X) ->
+handle_answer(Pkt, Req, [$C|_], Peer, Group, send_detach = Name, _, X) ->
     {Pid, Ref} = X,
     Pid ! {Ref, answer(Pkt, Req, Peer, Name, Group)}.
 
@@ -1503,18 +1481,18 @@ app(Req, _, Dict0) ->
     Dict = dict(Req, Dict0),
     Dict:id().
 
-%% handle_error/6
+%% handle_error/7
 
-handle_error(timeout = Reason, _Req, [$C|_], _Peer, _, Time) ->
+handle_error(timeout = Reason, _Req, [$C|_], _Peer, _, _, Time) ->
     Now = diameter_lib:now(),
     {Reason, {diameter_lib:timestamp(Time),
               diameter_lib:timestamp(Now),
               diameter_lib:micro_diff(Now, Time)}};
 
-handle_error(Reason, _Req, [$C|_], _Peer, _, _Time) ->
+handle_error(Reason, _Req, [$C|_], _Peer, _, _, _Time) ->
     {error, Reason}.
 
-%% handle_request/3
+%% handle_request/4
 
 %% Note that diameter will set Result-Code and Failed-AVPs if
 %% #diameter_packet.errors is non-null.
@@ -1522,7 +1500,10 @@ handle_error(Reason, _Req, [$C|_], _Peer, _, _Time) ->
 handle_request(#diameter_packet{header = H, avps = As}
                = Pkt,
                _,
-               {_Ref, Caps}) ->
+               {_Ref, Caps},
+               #group{encoding = E,
+                      server_decoding = D}
+               = Grp) ->
     #diameter_header{end_to_end_id = EI,
                      hop_by_hop_id = HI}
         = H,
@@ -1530,8 +1511,8 @@ handle_request(#diameter_packet{header = H, avps = As}
     V = EI bsr B,  %% assert
     V = HI bsr B,  %%
     #diameter_caps{origin_state_id = {_,[Id]}} = Caps,
-    {D,_} = T = origin(Id),
-    wrap(T, H, request(to_map(D, Pkt), [H|As], Caps)).
+    {D,E} = T = origin(Id),  %% assert
+    wrap(T, H, request(to_map(Pkt, Grp), [H|As], Caps)).
 
 wrap(Id, H, {Tag, Action, Post}) ->
     {Tag, wrap(Id, H, Action), Post};
@@ -1585,8 +1566,7 @@ base_to_nas(Msg, _) ->
 %% request/3
 
 %% send_experimental_result
-request(#{':name' := 'ACR',
-          'Accounting-Record-Number' := 5},
+request(['ACR' | #{'Accounting-Record-Number' := 5}],
         [Hdr | Avps],
         #diameter_caps{origin_host = {OH, _},
                        origin_realm = {OR, _}}) ->
@@ -1619,16 +1599,14 @@ request(Msg, _Avps, Caps) ->
 %% request/2
 
 %% send_nok
-request(#{':name' := 'ACR',
-          'Accounting-Record-Number' := 0},
+request(['ACR' | #{'Accounting-Record-Number' := 0}],
         _) ->
     {eval_packet, {protocol_error, ?INVALID_AVP_BITS}, [fun log/2, invalid]};
 
 %% send_bad_answer
-request(#{':name' := 'ACR',
-          'Session-Id' := SId,
-          'Accounting-Record-Type' := RT,
-          'Accounting-Record-Number' := 2 = RN},
+request(['ACR' | #{'Session-Id' := SId,
+                   'Accounting-Record-Type' := RT,
+                   'Accounting-Record-Number' := 2 = RN}],
         #diameter_caps{origin_host = {OH, _},
                        origin_realm = {OR, _}}) ->
     Ans = ['ACA', {'Result-Code', ?SUCCESS},
@@ -1642,10 +1620,9 @@ request(#{':name' := 'ACR',
                              msg = Ans}};
 
 %% send_eval
-request(#{':name' := 'ACR',
-          'Session-Id' := SId,
-          'Accounting-Record-Type' := RT,
-          'Accounting-Record-Number' := 3 = RN},
+request(['ACR' | #{'Session-Id' := SId,
+                   'Accounting-Record-Type' := RT,
+                   'Accounting-Record-Number' := 3 = RN}],
         #diameter_caps{origin_host = {OH, _},
                        origin_realm = {OR, _}}) ->
     Ans = ['ACA', {'Result-Code', ?SUCCESS},
@@ -1657,10 +1634,9 @@ request(#{':name' := 'ACR',
     {eval, {reply, Ans}, {erlang, now, []}};
 
 %% send_ok
-request(#{':name' := 'ACR',
-          'Session-Id' := SId,
-          'Accounting-Record-Type' := RT,
-          'Accounting-Record-Number' := 1 = RN},
+request(['ACR' | #{'Session-Id' := SId,
+                   'Accounting-Record-Type' := RT,
+                   'Accounting-Record-Number' := 1 = RN}],
         #diameter_caps{origin_host = {OH, _},
                        origin_realm = {OR, _}}) ->
     {reply, ['ACA', {'Result-Code', ?SUCCESS},
@@ -1671,8 +1647,7 @@ request(#{':name' := 'ACR',
                     {'Accounting-Record-Number', RN}]};
 
 %% send_protocol_error
-request(#{':name' := 'ACR',
-          'Accounting-Record-Number' := 4},
+request(['ACR' | #{'Accounting-Record-Number' := 4}],
         #diameter_caps{origin_host = {OH, _},
                        origin_realm = {OR, _}}) ->
     Ans = ['answer-message', {'Result-Code', ?TOO_BUSY},
@@ -1680,46 +1655,39 @@ request(#{':name' := 'ACR',
                              {'Origin-Realm', OR}],
     {reply, Ans};
 
-request(#{':name' := 'ASR',
-          'Session-Id' := SId}
-        = Req,
+request(['ASR' | #{'Session-Id' := SId} = Avps],
         #diameter_caps{origin_host = {OH, _},
                        origin_realm = {OR, _}}) ->
     {reply, ['ASA', {'Result-Code', ?SUCCESS},
                     {'Session-Id', SId},
                     {'Origin-Host', OH},
                     {'Origin-Realm', OR},
-                    {'AVP', maps:get('AVP', Req, [])}]};
+                    {'AVP', maps:get('AVP', Avps, [])}]};
 
 %% send_invalid_reject
-request(#{':name' := 'STR',
-          'Termination-Cause' := ?USER_MOVED},
+request(['STR' | #{'Termination-Cause' := ?USER_MOVED}],
         _Caps) ->
     {protocol_error, ?TOO_BUSY};
 
 %% send_noreply
-request(#{':name' := 'STR',
-          'Termination-Cause' := T},
+request(['STR' | #{'Termination-Cause' := T}],
         _Caps)
   when T /= ?LOGOUT ->
     discard;
 
 %% send_destination_5
-request(#{':name' := 'STR',
-          'Destination-Realm' := R},
+request(['STR' | #{'Destination-Realm' := R}],
         #diameter_caps{origin_realm = {OR, _}})
   when R /= undefined, R /= OR ->
     {protocol_error, ?REALM_NOT_SERVED};
 
 %% send_destination_6
-request(#{':name' := 'STR',
-          'Destination-Host' := [H]},
+request(['STR' | #{'Destination-Host' := [H]}],
         #diameter_caps{origin_host = {OH, _}})
   when H /= OH ->
     {protocol_error, ?UNABLE_TO_DELIVER};
 
-request(#{':name' := 'STR',
-          'Session-Id' := SId},
+request(['STR' | #{'Session-Id' := SId}],
         #diameter_caps{origin_host  = {OH, _},
                        origin_realm = {OR, _}}) ->
     {reply, ['STA', {'Result-Code', ?SUCCESS},
@@ -1728,7 +1696,7 @@ request(#{':name' := 'STR',
                     {'Origin-Realm', OR}]};
 
 %% send_error/send_timeout
-request(#{':name' := 'RAR'}, _Caps) ->
+request(['RAR' | #{}], _Caps) ->
     receive after 2000 -> {protocol_error, ?TOO_BUSY} end.
 
 %% message/3