Answer 5xxx errors with application_opt() request_errors = answer

RFC 3588 allowed only 3xxx result codes in an answer-message (that is,
an answer that sets the E-bit) while RFC 6733 also allows 5xxx result
codes. Setting request_errors = answer tells diameter to answer 5xxx
errors itself. Returning {answer_message, integer()} from a
handle_request callback allows both 3xxx and 5xxx result codes to be
set. {protocol_error, integer()} is retained for 3xxx result codes.

6 files changed, 144 insertions, 95 deletions

diff --git a/lib/diameter/doc/src/diameter.xml b/lib/diameter/doc/src/diameter.xml
index accf21cf98..379e9f0738 100644
--- a/lib/diameter/doc/src/diameter.xml
+++ b/lib/diameter/doc/src/diameter.xml
@@ -188,7 +188,7 @@ Defaults to the value of the <c>alias</c> option if unspecified.</p>
 <item>
 <p>
 Specifies whether or not the &app_pick_peer;
-application callback can modify the application state,
+application callback can modify the application state.
 Defaults to <c>false</c> if unspecified.</p>
 
 <note>
@@ -226,22 +226,37 @@ question is as if a callback had taken place and returned
 Defaults to <c>report</c> if unspecified.</p>
 </item>
 
-<tag><c>{request_errors, answer_3xxx|callback}</c></tag>
+<tag><c>{request_errors, answer_3xxx|answer|callback}</c></tag>
 <item>
 <p>
 Determines the manner in which incoming requests are handled when an
-error other than 3007, DIAMETER_APPLICATION_UNSUPPORTED. (With which no
-application callback module can be associated.)</p>
+error other than 3007, DIAMETER_APPLICATION_UNSUPPORTED (which cannot
+be associated with an application callback module), is detected.</p>
 
 <p>
-If <c>answer_3xxx</c> then the request is answered by diameter
-without a &app_handle_request; callback taking place if a 3xxx series
-error (protocol errors) is detected.
-If <c>callback</c> then even 3xxx errors result in an application
-&app_handle_request; callback.</p>
+If <c>answer_3xxx</c> then requests are answered without a
+&app_handle_request; callback taking place.
+If <c>answer</c> then even 5xxx errors are answered without a
+callback unless the connection in question has configured the RFC 3588
+common dictionary as noted below.
+If <c>callback</c> then a &app_handle_request; callback always takes
+place and the return value determines the answer sent to the peer.</p>
 
 <p>
 Defaults to <c>answer_3xxx</c> if unspecified.</p>
+
+<note>
+<p>
+Answers sent by diameter set the E-bit in the Diameter Header.
+Since RFC 3588 allowed only 3xxx result codes in an
+<c>answer-message</c>, <c>answer</c> has the same semantics as
+<c>answer_3xxx</c> if the peer connection in question has configured
+the RFC 3588 common dictionary, <c>diameter_gen_base_rfc3588</c>.
+RFC 6733 allows both 3xxx and 5xxx result codes in an
+<c>answer-message</c> so a connection configured with the RFC 6733
+common dictionary, <c>diameter_gen_base_rfc6733</c>, does
+distinguish between <c>answer_3xxx</c> and <c>answer</c>.</p>
+</note>
 </item>
 
 </taglist>
diff --git a/lib/diameter/doc/src/diameter_app.xml b/lib/diameter/doc/src/diameter_app.xml
index 5c23c9d683..d0f1b22ebd 100644
--- a/lib/diameter/doc/src/diameter_app.xml
+++ b/lib/diameter/doc/src/diameter_app.xml
@@ -475,6 +475,7 @@ not selected.</p>
            | discard
            | {eval|eval_packet, Action, PostF}</v>
 <v>Reply   = {reply, &packet; | &message;}
+           | {answer_message, 3000..3999|5000..5999}
            | {protocol_error, 3000..3999}</v>
 <v>Opt     = &mod_call_opt;</v>
 <v>PostF   = &mod_evaluable;</v>
@@ -545,22 +546,25 @@ preserved in the outgoing answer, appropriate values otherwise
 being set by diameter.</p>
 </item>
 
-<tag><c>{protocol_error, 3000..3999}</c></tag>
+<tag><c>{answer_message, 3000..3999|5000..5999}</c></tag>
 <item>
 <p>
 Send an answer message to the peer containing the specified
-protocol error.
+Result-Code.
 Equivalent to</p>
 <pre>
 {reply, ['answer-message' | Avps]
 </pre>
 <p>
 where <c>Avps</c> sets the Origin-Host, Origin-Realm, the specified
-Result-Code and (if the request sent one) Session-Id AVP's.</p>
+Result-Code and (if the request contained one) Session-Id AVP's.</p>
 
 <p>
-Returning a non-3xxx value in a <c>protocol_error</c> tuple
-will cause the request process in question to fail.</p>
+Returning a value other than 3xxx or 5xxx will cause the request
+process in question to fail, as will returning a 5xxx value if the
+peer connection in question has been configured with the RFC 3588
+common dictionary <c>diameter_gen_base_rfc3588</c>.
+(Since RFC 3588 only allows 3xxx values in an answer-message.)</p>
 </item>
 
 <tag><c>{relay, Opts}</c></tag>
@@ -613,11 +617,20 @@ containing the encoded binary.
 The return value is ignored.</p>
 </item>
 
+<tag><c>{protocol_error, 3000..3999}</c></tag>
+<item>
+<p>
+Equivalent to <c>{answer_message, 3000..3999}</c>.</p>
+</item>
+
 </taglist>
 
+<note>
 <p>
-Note that protocol errors detected by diameter will result in an
-answer message without <c>handle_request/3</c> being invoked.</p>
+Requests containing errors may be answered by diameter, without a
+callback taking place, depending on the value of the
+&mod_application_opt; <c>request_errors</c>.</p>
+</note>
 
 </desc>
 </func>
diff --git a/lib/diameter/include/diameter.hrl b/lib/diameter/include/diameter.hrl
index 513665cec1..79c4dce541 100644
--- a/lib/diameter/include/diameter.hrl
+++ b/lib/diameter/include/diameter.hrl
@@ -144,5 +144,5 @@
          id,         %% 32-bit unsigned application identifier = Dict:id()
          mutable = false, %% boolean(), do traffic callbacks modify state?
          options = [{answer_errors, report},      %% | callback | discard
-                    {request_errors, answer_3xxx}]}). %% | callback
+                    {request_errors, answer_3xxx}]}). %% | callback | answer
 -endif. %% -ifdef(diameter_hrl).
diff --git a/lib/diameter/src/base/diameter.erl b/lib/diameter/src/base/diameter.erl
index 7359688404..c67fba5f89 100644
--- a/lib/diameter/src/base/diameter.erl
+++ b/lib/diameter/src/base/diameter.erl
@@ -307,7 +307,7 @@ call(SvcName, App, Message) ->
     | {state, any()}
     | {call_mutates_state, boolean()}
     | {answer_errors, callback|report|discard}
-    | {request_errors, callback|answer_3xxx}.
+    | {request_errors, answer_3xxx|answer|callback}.
 
 -type app_alias()
    :: any().
diff --git a/lib/diameter/src/base/diameter_config.erl b/lib/diameter/src/base/diameter_config.erl
index 889c75e3da..9f73815756 100644
--- a/lib/diameter/src/base/diameter_config.erl
+++ b/lib/diameter/src/base/diameter_config.erl
@@ -670,17 +670,17 @@ app_acc({application, Opts}, Acc) ->
     [Dict, Mod] = get_opt([dictionary, module], Opts),
     Alias = get_opt(alias, Opts, Dict),
     ModS  = get_opt(state, Opts, Alias),
-    M = get_opt(call_mutates_state, Opts, false),
-    A = get_opt(answer_errors, Opts, report),
-    R = get_opt(request_errors, Opts, answer_3xxx),
+    M = get_opt(call_mutates_state, Opts, false, [true]),
+    A = get_opt(answer_errors, Opts, report, [callback, discard]),
+    P = get_opt(request_errors, Opts, answer_3xxx, [answer, callback]),
     [#diameter_app{alias = Alias,
                    dictionary = Dict,
                    id = cb(Dict, id),
                    module = init_mod(Mod),
                    init_state = ModS,
-                   mutable = init_mutable(M),
-                   options = [{answer_errors, init_answers(A)},
-                              {request_errors, init_request_errors(R)}]}
+                   mutable = M,
+                   options = [{answer_errors, A},
+                              {request_errors, P}]}
      | Acc];
 app_acc(_, Acc) ->
     Acc.
@@ -709,27 +709,16 @@ init_cb(List) ->
                    V <- [proplists:get_value(F, List, D)]],
     #diameter_callback{} = list_to_tuple([diameter_callback | Values]).
 
-init_mutable(M)
-  when M == true;
-       M == false ->
-    M;
-init_mutable(M) ->
-    ?THROW({call_mutates_state, M}).
-
-init_answers(A)
-  when callback == A;
-       report == A;
-       discard == A ->
-    A;
-init_answers(A) ->
-    ?THROW({answer_errors, A}).
-
-init_request_errors(P)
-  when callback == P;
-       answer_3xxx == P ->
-    P;
-init_request_errors(P) ->
-    ?THROW({request_errors, P}).
+%% Retreive and validate.
+get_opt(Key, List, Def, Other) ->
+    init_opt(Key, get_opt(Key, List, Def), [Def|Other]).
+
+init_opt(_, V, [V|_]) ->
+    V;
+init_opt(Name, V, [_|Vals]) ->
+    init_opt(Name, V, Vals);
+init_opt(Name, V, []) ->
+    ?THROW({Name, V}).
 
 %% Get a single value at the specified key.
 get_opt(Keys, List)
diff --git a/lib/diameter/src/base/diameter_traffic.erl b/lib/diameter/src/base/diameter_traffic.erl
index c70fad8f83..f527f7c754 100644
--- a/lib/diameter/src/base/diameter_traffic.erl
+++ b/lib/diameter/src/base/diameter_traffic.erl
@@ -190,19 +190,21 @@ recv_request(TPid,
     send_A(recv_R(diameter_service:find_incoming_app(PeerT, TPid, Id, Apps),
                   TPid,
                   Pkt,
+                  Dict0,
                   RecvData),
            TPid,
            Dict0,
            RecvData).
 
-%% recv_R/4
+%% recv_R/5
 
 recv_R({#diameter_app{id = Id, dictionary = Dict} = App, Caps},
        TPid,
        Pkt0,
+       Dict0,
        RecvData) ->
     Pkt = errors(Id, diameter_codec:decode(Id, Dict, Pkt0)),
-    {Caps, Pkt, App, recv_R(App, TPid, Caps, RecvData, Pkt)};
+    {Caps, Pkt, App, recv_R(App, TPid, Dict0, Caps, RecvData, Pkt)};
 %% Note that the decode is different depending on whether or not Id is
 %% ?APP_ID_RELAY.
 
@@ -214,11 +216,12 @@ recv_R(#diameter_caps{}
        _TPid,
        #diameter_packet{errors = Es}
        = Pkt,
+       _Dict0,
        _RecvData) ->
     {Caps, Pkt#diameter_packet{avps = collect_avps(Pkt),
                                errors = [3007 | Es]}};
 
-recv_R(false = No, _, _, _) ->  %% transport has gone down
+recv_R(false = No, _, _, _, _) ->  %% transport has gone down
     No.
 
 collect_avps(Pkt) ->
@@ -229,21 +232,24 @@ collect_avps(Pkt) ->
             As
     end.
 
-%% recv_R/5
+%% recv_R/6
 
-%% Answer 3xxx errors ourselves ...
-recv_R(#diameter_app{options = [_, {request_errors, answer_3xxx} | _]},
+%% Answer errors ourselves ...
+recv_R(#diameter_app{options = [_, {request_errors, E} | _]},
        _TPid,
+       Dict0,
        _Caps,
        _RecvData,
        #diameter_packet{errors = [RC|_]})  %% a detected 3xxx is hd
-  when 3 == RC div 1000 ->
-    {{protocol_error, RC}, [], []};
+  when E == answer, (Dict0 /= ?BASE orelse 3 == RC div 1000);
+       E == answer_3xxx, 3 == RC div 1000 ->
+    {{answer_message, rc(RC)}, [], []};
 
 %% ... or make a handle_request callback. Note that
 %% Pkt#diameter_packet.msg = undefined in the 3001 case.
 recv_R(App,
        TPid,
+       _Dict0,
        Caps,
        #recvdata{service_name = SvcName},
        Pkt) ->
@@ -252,6 +258,11 @@ recv_R(App,
                [],
                []).
 
+rc({N,_}) ->
+    N;
+rc(N) ->
+    N.
+
 %% errors/1
 %%
 %% Look for additional errors in a decoded message, prepending the
@@ -331,8 +342,13 @@ request_cb({reply, _Ans} = T, _App, EvalPktFs, EvalFs) ->
     {T, EvalPktFs, EvalFs};
 
 %% An 3xxx result code, for which the E-bit is set in the header.
-request_cb({protocol_error, RC} = T, _App, EvalPktFs, EvalFs)
+request_cb({protocol_error, RC}, _App, EvalPktFs, EvalFs)
   when 3 == RC div 1000 ->
+    {{answer_message, RC}, EvalPktFs, EvalFs};
+
+request_cb({answer_message, RC} = T, _App, EvalPktFs, EvalFs)
+  when 3 == RC div 1000;
+       5 == RC div 1000 ->
     {T, EvalPktFs, EvalFs};
 
 %% RFC 3588 says we must reply 3001 to anything unrecognized or
@@ -340,7 +356,7 @@ request_cb({protocol_error, RC} = T, _App, EvalPktFs, EvalFs)
 %% backwards compatibility for this, protocol_error the documented
 %% alternative.
 request_cb(noreply, _App, EvalPktFs, EvalFs) ->
-    {{protocol_error, 3001}, EvalPktFs, EvalFs};
+    {{answer_message, 3001}, EvalPktFs, EvalFs};
 
 %% Relay a request to another peer. This is equivalent to doing an
 %% explicit call/4 with the message in question except that (1) a loop
@@ -372,15 +388,16 @@ request_cb({eval_packet, RC, F}, App, Fs, EvalFs) ->
 request_cb({eval, RC, F}, App, EvalPktFs, Fs) ->
     request_cb(RC, App, EvalPktFs, [F|Fs]);
 
-request_cb(T, #diameter_app{module = ModX}, _, _) ->
-    ?ERROR({invalid_return, T, {ModX, handle_request}}).
+request_cb(T, App, _, _) ->
+    ?ERROR({invalid_return, T, handle_request, App}).
 
 %% send_A/4
 
 send_A({Caps, Pkt}, TPid, Dict0, _RecvData) ->  %% unsupported application
     #diameter_packet{errors = [RC|_]} = Pkt,
-    send_A(protocol_error(RC, Caps, Dict0, Pkt),
+    send_A(answer_message(RC, Caps, Dict0, Pkt),
            TPid,
+           Dict0,
            Pkt,
            [],
            []);
@@ -388,6 +405,7 @@ send_A({Caps, Pkt}, TPid, Dict0, _RecvData) ->  %% unsupported application
 send_A({Caps, Pkt, App, {T, EvalPktFs, EvalFs}}, TPid, Dict0, RecvData) ->
     send_A(answer(T, Caps, Pkt, App, Dict0, RecvData),
            TPid,
+           Dict0,
            Pkt,
            EvalPktFs,
            EvalFs);
@@ -395,10 +413,10 @@ send_A({Caps, Pkt, App, {T, EvalPktFs, EvalFs}}, TPid, Dict0, RecvData) ->
 send_A(_, _, _, _) ->
     ok.
 
-%% send_A/5
+%% send_A/6
 
-send_A(T, TPid, ReqPkt, EvalPktFs, EvalFs) ->
-    reply(T, TPid, EvalPktFs, ReqPkt),
+send_A(T, TPid, Dict0, ReqPkt, EvalPktFs, EvalFs) ->
+    reply(T, TPid, Dict0, EvalPktFs, ReqPkt),
     lists:foreach(fun diameter_lib:eval/1, EvalFs).
 
 %% answer/6
@@ -420,8 +438,12 @@ answer({call, Opts}, Caps, Pkt, App, Dict0, RecvData) ->
            Dict0,
            RecvData);
 
-answer({protocol_error, RC}, Caps, Pkt, _App, Dict0, _RecvData) ->
-    protocol_error(RC, Caps, Dict0, Pkt).
+%% RFC 3588 only allows 3xxx errors in an answer-message. RFC 6733
+%% added the possibility of setting 5xxx.
+answer({answer_message, RC} = T, Caps, Pkt, App, Dict0, _RecvData)  ->
+    Dict0 /= ?BASE orelse 3 == RC div 1000
+        orelse ?ERROR({invalid_return, T, handle_request, App}),
+    answer_message(RC, Caps, Dict0, Pkt).
 
 %% dict/3
 
@@ -451,9 +473,9 @@ is_answer_message(Rec, Dict) ->
         error:_ -> false
     end.
 
-%% protocol_error/4
+%% answer_message/4
 
-protocol_error(RC,
+answer_message(RC,
                #diameter_caps{origin_host  = {OH,_},
                               origin_realm = {OR,_}},
                Dict0,
@@ -471,7 +493,7 @@ protocol_error(RC,
 %%      identified a configuration problem.
 
 resend(true, _Opts, Caps, Pkt, _App, Dict0, _RecvData) ->
-    protocol_error(3005, Caps, Dict0, Pkt);
+    answer_message(3005, Caps, Dict0, Pkt);
 
 %% 6.1.8.  Relaying and Proxying Requests
 %%
@@ -528,7 +550,7 @@ resend(#diameter_packet{bin = B}
 
 %% Or not: DIAMETER_UNABLE_TO_DELIVER.
 resend(_, Caps, Dict0, Pkt) ->
-    protocol_error(3002, Caps, Dict0, Pkt).
+    answer_message(3002, Caps, Dict0, Pkt).
 
 %% is_loop/5
 %%
@@ -551,32 +573,32 @@ is_loop(Code, Vid, OH, Dict0, [_ | Avps])
 is_loop(Code, Vid, OH, Dict0, Avps) ->
     is_loop(Code, Vid, Dict0:avp(encode, OH, 'Route-Record'), Dict0, Avps).
 
-%% reply/4
+%% reply/5
 
 %% Local answer ...
-reply({Dict, Ans}, TPid, Fs, ReqPkt) ->
-    reply(Ans, Dict, TPid, Fs, ReqPkt);
+reply({Dict, Ans}, TPid, Dict0, Fs, ReqPkt) ->
+    reply(Ans, Dict, TPid, Dict0, Fs, ReqPkt);
 
 %% ... or relayed.
-reply(#diameter_packet{} = Pkt, TPid, Fs, _ReqPkt) ->
+reply(#diameter_packet{} = Pkt, TPid, _Dict0, Fs, _ReqPkt) ->
     eval_packet(Pkt, Fs),
     send(TPid, Pkt).
 
-%% reply/5
+%% reply/6
 %%
 %% Send a locally originating reply.
 
 %% Skip the setting of Result-Code and Failed-AVP's below. This is
 %% undocumented and shouldn't be relied on.
-reply([Msg], Dict, TPid, Fs, ReqPkt)
+reply([Msg], Dict, TPid, Dict0, Fs, ReqPkt)
   when is_list(Msg);
        is_tuple(Msg) ->
-    reply(Msg, Dict, TPid, Fs, ReqPkt#diameter_packet{errors = []});
+    reply(Msg, Dict, TPid, Dict0, Fs, ReqPkt#diameter_packet{errors = []});
 
 %% No errors or a diameter_header/avp list.
-reply(Msg, Dict, TPid, Fs, ReqPkt) ->
+reply(Msg, Dict, TPid, Dict0, Fs, ReqPkt) ->
     Pkt = encode(Dict, reset(make_answer_packet(Msg, ReqPkt), Dict), Fs),
-    incr(send, Pkt, Dict, TPid),  %% count result codes in sent answers
+    incr(send, Pkt, Dict, TPid, Dict0),  %% count outgoing result codes
     send(TPid, Pkt).
 
 %% reset/2
@@ -915,31 +937,43 @@ find(Pred, [H|T]) ->
 
 %% Outgoing message as binary: don't count. (Sending binaries is only
 %% partially supported.)
-incr(_, #diameter_packet{msg = undefined}, _, _) ->
+incr(_, #diameter_packet{msg = undefined}, _, _, _) ->
     ok;
 
 %% Incoming with decode errors.
-incr(recv = D, #diameter_packet{header = H, errors = [_|_]}, _, TPid) ->
+incr(recv = D, #diameter_packet{header = H, errors = [_|_]}, _, TPid, _) ->
     incr(TPid, {diameter_codec:msg_id(H), D, error});
 
 %% Incoming without errors or outgoing. Outgoing with encode errors
 %% never gets here since encode fails.
-incr(Dir, Pkt, Dict, TPid) ->
+incr(Dir, Pkt, Dict, TPid, Dict0) ->
     #diameter_packet{header = #diameter_header{is_error = E}
                             = Hdr,
                      msg = Rec}
         = Pkt,
 
     RC = int(get_avp_value(Dict, 'Result-Code', Rec)),
-    PE = is_protocol_error(RC),
 
-    %% Check that Result-Code matches E-bit.
-    (not (E orelse PE))        %% non-3xxx answer without E-bit
-        orelse (E andalso PE)  %% 3xxx answer with E-bit
+    %% Exit on an improper Result-Code.
+    is_result(RC, E, Dict0)
         orelse x({invalid_error_bit, RC}, answer, [Dir, Pkt]),
 
     irc(TPid, Hdr, Dir, rc_counter(Dict, Rec, RC)).
 
+%% No E-bit: can't be 3xxx.
+is_result(RC, false, _Dict0) ->
+    RC < 3000 orelse 4000 =< RC;
+
+%% E-bit in RFC 3588: only 3xxx.
+is_result(RC, true, ?BASE) ->
+    3000 =< RC andalso RC < 4000;
+
+%% E-bit in RFC 6733: 3xxx or 5xxx.
+is_result(RC, true, _) ->
+    3000 =< RC andalso RC < 4000
+        orelse
+        5000 =< RC andalso RC < 6000.
+
 irc(_, _, _, undefined) ->
     false;
 
@@ -991,9 +1025,6 @@ int(N)
 int(_) ->
     undefined.
 
-is_protocol_error(RC) ->
-    3000 =< RC andalso RC < 4000.
-
 -spec x(any(), atom(), list()) -> no_return().
 
 %% Warn and exit request process on errors in an incoming answer.
@@ -1143,7 +1174,7 @@ send_R({eval_packet, RC, F}, Pkt, T, Opts, Caller, SvcName, Fs) ->
     send_R(RC, Pkt, T, Opts, Caller, SvcName, [F|Fs]);
 
 send_R(E, _, {_, _, App}, _, _, _, _) ->
-    ?ERROR({invalid_return, prepare_request, App, E}).
+    ?ERROR({invalid_return, E, prepare_request, App}).
 
 %% make_prepare_packet/2
 %%
@@ -1295,19 +1326,20 @@ handle_answer(SvcName,
               = App,
               {answer, Req, Dict0, Pkt}) ->
     Mod = dict(Dict, Dict0, Pkt),
-    answer(errors(Id, diameter_codec:decode(Mod, Pkt)),
-           SvcName,
-           Mod,
-           App,
-           Req).
+    handle_A(errors(Id, diameter_codec:decode(Mod, Pkt)),
+             SvcName,
+             Mod,
+             Dict0,
+             App,
+             Req).
 
 %% We don't really need to do a full decode if we're a relay and will
 %% just resend with a new hop by hop identifier, but might a proxy
 %% want to examine the answer?
 
-answer(Pkt, SvcName, Dict, App, #request{transport = TPid} = Req) ->
+handle_A(Pkt, SvcName, Dict, Dict0, App, #request{transport = TPid} = Req) ->
     try
-        incr(recv, Pkt, Dict, TPid) %% count result codes in received answers
+        incr(recv, Pkt, Dict, TPid, Dict0) %% count incoming result codes
     of
         _ -> answer(Pkt, SvcName, App, Req)
     catch
@@ -1505,7 +1537,7 @@ retransmit({eval_packet, RC, F}, Transport, Req, SvcName, Timeout, Fs) ->
     retransmit(RC, Transport, Req, SvcName, Timeout, [F|Fs]);
 
 retransmit(T, {_, _, App}, _, _, _, _) ->
-    ?ERROR({invalid_return, prepare_retransmit, App, T}).
+    ?ERROR({invalid_return, T, prepare_retransmit, App}).
 
 resend_request(Pkt0,
                {TPid, Caps, #diameter_app{dictionary = Dict}},