pfcp_peer: implement the Heartbeat procedure

Change-Id: Ic4682d49f2e1df08d241500b7b4e75edadaeb91a
---
M src/pfcp_peer.erl
1 file changed, 32 insertions(+), 3 deletions(-)

diff --git a/src/pfcp_peer.erl b/src/pfcp_peer.erl
index b190f12..8c29a9f 100644
--- a/src/pfcp_peer.erl
+++ b/src/pfcp_peer.erl
@@ -169,7 +169,8 @@
 %% Handle incoming PFCP PDU(s)
 connecting(info, {udp, Sock, FromIp, FromPort, Data},
            #peer_state{sock = Sock} = S) ->
-    case decode_pdu(Data, {FromIp, FromPort}, S) of
+    PDU = decode_pdu(Data, {FromIp, FromPort}, S),
+    case PDU of
         #pfcp{type = association_setup_response,
               ie = #{pfcp_cause := 'Request accepted',
                      recovery_time_stamp := #recovery_time_stamp{time = RRTS}}} ->
@@ -180,7 +181,13 @@
               ie = #{pfcp_cause := Cause}} ->
             ?LOG_ERROR("Rx Association Setup Response (~p)", [Cause]),
             {stop, {shutdown, assoc_setup_nack}};
-        PDU ->
+        %% 3GPP TS 29.244, 6.2.2.2 Heartbeat Request
+        %% A CP function or UP function shall be prepared to receive a Heartbeat Request
+        %% at any time (even from unknown peers) and it shall reply with a Heartbeat Response.
+        #pfcp{type = heartbeat_request} ->
+            recv_heartbeat_request(PDU, {FromIp, FromPort}, S),
+            {keep_state, S};
+        _ ->
             ?LOG_NOTICE("Rx unexpected PFCP PDU: ~p", [PDU]),
             {keep_state, S}
     end;
@@ -216,7 +223,13 @@
 connected(info, {udp, Sock, FromIp, FromPort, Data},
           #peer_state{sock = Sock} = S) ->
     PDU = decode_pdu(Data, {FromIp, FromPort}, S),
-    route_pdu(PDU, S),
+    case PDU of
+        %% 3GPP TS 29.244, 6.2.2.2 Heartbeat Request
+        #pfcp{type = heartbeat_request} ->
+            recv_heartbeat_request(PDU, {FromIp, FromPort}, S);
+        _ ->
+            route_pdu(PDU, S)
+    end,
     {keep_state, S};
 
 %% Catch-all handler for this state
@@ -409,4 +422,20 @@
 send_session_delete_req(SEID, S) ->
     send_pdu(SEID, {session_deletion_request, []}, S).
 
+
+%% 6.2.2 Heartbeat Procedure
+%% 7.4.2 Heartbeat Messages
+recv_heartbeat_request(#pfcp{type = heartbeat_request,
+                             seq_no = SeqNr,
+                             ie = ReqIEs},
+                       {FromIp, FromPort},
+                       #peer_state{loc_rts = LRTS} = S) ->
+    ?LOG_INFO("Rx Heartbeat Request from ~p:~p: ~p", [FromIp, FromPort, ReqIEs]),
+    RspIEs = #{recovery_time_stamp => #recovery_time_stamp{time = LRTS}},
+    %% Fake #peer_state to force the right destination and SeqNr
+    {Result, _} = send_pdu({heartbeat_response, RspIEs},
+                           S#peer_state{seq_nr = SeqNr,
+                                        rem_addr = FromIp}),
+    Result.
+
 %% vim:set ts=4 sw=4 et:

