Allow encode of decoded diameter_avp list

The decode of an incoming request in a non-relay application results in
a deep list of diameter_avp records. Encoding such a list resulted in a
function_clause error in diameter_codec:pack_avp/1, which expected a
flat list. The list is only flat in the relay case, or in the absence of
AVPs of type Grouped.

This is also related to code that exists but isn't documented. It's
documented that a diameter_app(3) handle_request callback can return
{relay, Opts} to relay a request received in the relay application.
What's not documented is that it can also return {proxy|resend, Opts} in
a non-relay application, but this leads to encode failure when there are
Grouped AVPs. This shouldn't be interpreted as meaning that proxy|resend
are now supported: they aren't. The two extra terms are a historical
relic that should probably be removed. Neither are generally usable
since, for example, a proxy agent may want to modify a request before
resending it. A specific handle_request return is not needed to
implement a proxy agent. Even {relay, Opts} isn't strictly necessary.

1 files changed, 2 insertions, 0 deletions

diff --git a/lib/diameter/src/base/diameter_codec.erl b/lib/diameter/src/base/diameter_codec.erl
index dd9039d7dc..9bc8178230 100644
--- a/lib/diameter/src/base/diameter_codec.erl
+++ b/lib/diameter/src/base/diameter_codec.erl
@@ -582,6 +582,8 @@ split_data(Bin, Len) ->
 %% 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)});