Fix setting of Failed-AVP on {answer_message, 5xxx} from handle_request

RFC 6733 says that certain 5xxx result codes must be accompanied by
Failed-AVP, and decode populates #diameter_packet.errors with
Result-Code/AVP pairs for errors it detects. However, Failed-AVP was not
set in the outgoing answer if the handle_request callback returned
{answer_message, 5xxx}. It is now set with the AVP from the first pair
with the specified Result-Code, if found.

Note that {answer_message, 5xxx} doesn't handle all cases in which a
5xxx answer is required, only that in which the setting above is
appropriate. If it isn't then handle_request should construct its answer
and return {reply, Ans}.

1 files changed, 16 insertions, 6 deletions

diff --git a/lib/diameter/src/base/diameter_traffic.erl b/lib/diameter/src/base/diameter_traffic.erl
index 820d37535a..0b15e68ec7 100644
--- a/lib/diameter/src/base/diameter_traffic.erl
+++ b/lib/diameter/src/base/diameter_traffic.erl
@@ -479,10 +479,9 @@ answer_message(RC,
                #diameter_caps{origin_host  = {OH,_},
                               origin_realm = {OR,_}},
                Dict0,
-               #diameter_packet{avps = Avps}
-               = Pkt) ->
+               Pkt) ->
     ?LOG({error, RC}, Pkt),
-    {Dict0, answer_message(OH, OR, RC, Dict0, Avps)}.
+    {Dict0, answer_message(OH, OR, RC, Dict0, Pkt)}.
 
 %% resend/7
 
@@ -861,12 +860,14 @@ failed(Rec, FailedAvp, Dict) ->
 
 %% answer_message/5
 
-answer_message(OH, OR, RC, Dict0, Avps) ->
+answer_message(OH, OR, RC, Dict0, #diameter_packet{avps = Avps,
+                                                   errors = Es}) ->
     {Code, _, Vid} = Dict0:avp_header('Session-Id'),
     ['answer-message', {'Origin-Host', OH},
                        {'Origin-Realm', OR},
-                       {'Result-Code', RC}
-                       | session_id(Code, Vid, Dict0, Avps)].
+                       {'Result-Code', RC}]
+        ++ session_id(Code, Vid, Dict0, Avps)
+        ++ failed_avp(RC, Es).
 
 session_id(Code, Vid, Dict0, Avps)
   when is_list(Avps) ->
@@ -878,6 +879,15 @@ session_id(Code, Vid, Dict0, Avps)
             []
     end.
 
+%% Note that this should only match 5xxx result codes currently but
+%% don't bother distinguishing this case.
+failed_avp(RC, [{RC, Avp} | _]) ->
+    [{'Failed-AVP', [{'AVP', [Avp]}]}];
+failed_avp(RC, [_ | Es]) ->
+    failed_avp(RC, Es);
+failed_avp(_, [] = No) ->
+    No.
+
 %% find_avp/3
 
 find_avp(Code, Vid, Avps)