pfcp_peer: do not assign SEID=0, increment properly

Change-Id: I76b921047784e727d67cd6c6a5aeb6d827b65e56
---
M src/pfcp_peer.erl
1 file changed, 9 insertions(+), 3 deletions(-)

diff --git a/src/pfcp_peer.erl b/src/pfcp_peer.erl
index f379e69..aa33e3a 100644
--- a/src/pfcp_peer.erl
+++ b/src/pfcp_peer.erl
@@ -54,11 +54,13 @@
 %% 3GPP TS 29.244, section 4.2 "UDP Header and Port Numbers"
 -define(PFCP_PORT, 8805).
 
+-define(PFCP_SEID_MAX, 16#ffffffffffffffff).
+
 -type pfcp_session_rsp() :: ok | {error, term()}.
 
 -type pfcp_msg_type() :: atom().
 -type pfcp_seq_nr() :: 0..16#ffffff.
--type pfcp_seid() :: 0..16#ffffffffffffffff.
+-type pfcp_seid() :: 0..?PFCP_SEID_MAX.
 -type pfcp_f_seid() :: #f_seid{}.
 -type pfcp_ies() :: [term()] | map() | binary().
 -type pfcp_msg() :: {pfcp_msg_type(), pfcp_ies()}.
@@ -139,7 +141,7 @@
                                            {reuseaddr, true},
                                            {active, true}]),
     ?LOG_INFO("PFCP peer @ ~p will talk to UPF @ ~p", [LocAddr, RemAddr]),
-    {ok, connecting, #peer_state{seid = 0,
+    {ok, connecting, #peer_state{seid = 1, %% SEID=0 is special, see 7.2.2.4.2
                                  sock = Sock,
                                  loc_addr = LocAddr,
                                  rem_addr = RemAddr,
@@ -288,8 +290,12 @@
     Ref = erlang:monitor(process, Pid),
     NReg = dict:store(SEID, {Pid, Ref}, Reg),
     ?LOG_DEBUG("Allocated SEID ~p to process ~p", [SEID, Pid]),
+    NSEID = case SEID of
+        ?PFCP_SEID_MAX -> 1;
+        _ -> SEID + 1
+    end,
     S#peer_state{registry = NReg,
-                 seid = SEID + 1}.
+                 seid = NSEID}.
 
 
 -spec registry_del({pid(), reference()}, peer_state()) -> peer_state().

