Fix relay encode of decoded diameter_avp lists

Commit c74b593a fixed the problem that a decoded deep diameter_avp list
couldn't be encoded, but did so in the wrong way: there's no need to
reencode component AVPs since the Grouped AVP itself already contains
the encoded binary. The blunder caused diameter_codec:pack_avp/1 to fail
if the first element of the AVP list to be encoded was itself a list.

Thanks to Andrzej Trawiński for reporting the problem.

1 files changed, 14 insertions, 7 deletions

diff --git a/lib/diameter/src/base/diameter_codec.erl b/lib/diameter/src/base/diameter_codec.erl
index bf2fe8e7ca..2ad971a422 100644
--- a/lib/diameter/src/base/diameter_codec.erl
+++ b/lib/diameter/src/base/diameter_codec.erl
@@ -655,16 +655,23 @@ split_data(Bin, Len) ->
 
 %% The normal case here is data as an #diameter_avp{} list or an
 %% iolist, which are the cases that generated codec modules use. The
-%% other case is as a convenience in the relay case in which the
+%% other cases are a convenience in the relay case in which the
 %% dictionary doesn't know about specific AVP's.
 
-%% Grouped AVP whose components need packing ...
-pack_avp([#diameter_avp{} = A | Avps]) ->
-    pack_avp(A#diameter_avp{data = Avps});
-pack_avp(#diameter_avp{data = [#diameter_avp{} | _] = Avps} = A) ->
-    pack_avp(A#diameter_avp{data = encode_avps(Avps)});
+%% Decoded Grouped AVP with decoded components: ignore components
+%% since they're already encoded in the Grouped AVP.
+pack_avp([#diameter_avp{} = Grouped | _Components]) ->
+    pack_avp(Grouped);
 
-%% ... data as a type/value tuple ...
+%% Grouped AVP whose components need packing. It's intentional that
+%% this isn't equivalent to [Grouped | Components]: here the
+%% components need to be encoded before wrapping with the Grouped AVP,
+%% and the list is flat, nesting being accomplished in the data
+%% fields.
+pack_avp(#diameter_avp{data = [#diameter_avp{} | _] = Components} = Grouped) ->
+    pack_avp(Grouped#diameter_avp{data = encode_avps(Components)});
+
+%% Data as a type/value tuple ...
 pack_avp(#diameter_avp{data = {Type, Value}} = A)
   when is_atom(Type) ->
     pack_avp(A#diameter_avp{data = diameter_types:Type(encode, Value)});