Count discarded incoming messages

An incoming Diameter message is either a request, an answer to an
outstanding request, or an unexpected answer. The latter weren't
counted, but are now counted on keys of this form:

  {pid(), {{unknown, 0}, recv, discarded}}

The form of the second element is similar to those of other counters,
like:

  {{relay, 0|1}, send|recv, invalid_error_bit}

Compare this to the key used when counting known answers:

  {{ApplicationId, CommandCode, 0}, recv}

The application id and command code aren't included so as not to count
on arbitrary keys, a topic last visited in commit 49e8b11c.

2 files changed, 3 insertions, 1 deletions

diff --git a/lib/diameter/src/base/diameter_traffic.erl b/lib/diameter/src/base/diameter_traffic.erl
index 517daf6678..ad63e5b150 100644
--- a/lib/diameter/src/base/diameter_traffic.erl
+++ b/lib/diameter/src/base/diameter_traffic.erl
@@ -259,7 +259,8 @@ recv(false, #request{ref = Ref, handler = Pid} = Req, _, Pkt, Dict0, _) ->
 %% any others are discarded.
 
 %% ... or not.
-recv(false, false, _, _, _, _) ->
+recv(false, false, TPid, _, _, _) ->
+    incr(TPid, {{unknown, 0}, recv, discarded}),
     ok.
 
 %% spawn_request/4
diff --git a/lib/diameter/test/diameter_relay_SUITE.erl b/lib/diameter/test/diameter_relay_SUITE.erl
index 5acea3cdb6..7142239bbb 100644
--- a/lib/diameter/test/diameter_relay_SUITE.erl
+++ b/lib/diameter/test/diameter_relay_SUITE.erl
@@ -259,6 +259,7 @@ stats(?CLIENT, L) ->
      {{{0,274,1},send},1},   %% ASR (send_loop)
      {{{0,275,0},recv},4},   %% STA (send[1-4])
      {{{0,275,1},send},4},   %% STR (send[1-4])
+     {{{unknown,0},recv,discarded},1},  %% RAR (send_timeout_2)
      {{{0,257,0},recv,{'Result-Code',2001}},2},  %% CEA
      {{{0,258,0},recv,{'Result-Code',3002}},1},  %% RAA (send_timeout_1)
      {{{0,274,0},recv,{'Result-Code',3005}},1},  %% ASA (send_loop)