Close listening sockets at transport removal

The transport interface documented in diameter_transport(3) is used to
start/stop accepting/connecting transport processes: they're started
with a function call, and told to die with their parent process. In the
accepting case, both diameter_tcp and diameter_sctp start a listening
process when the first accepting transport is started. However, there's
no way for a listening process to find out that that it should stop
listening when transport configuration is removed.

Both diameter_tcp and diameter_sctp have used a timer to terminate the
listening process after all existing accepting processes have died as a
consequence of transport removal. The problem with this is that nothing
stops a new client from connecting before this, and also that no new
transport can succeed in opening the same listening port (eg.
reconfiguration) until the old listener dies.

This commit solves the problem by adding diameter_reg:subscribe/2, to
allow callers to subscribe to messages about added/removed associations.
A call to diameter:add_transport/2 results in a new child process that
registers a term that a listening process subscribes to. Transport
removal results in the death of the child, and the resulting
notification to the listener causes the latter to close its socket and
terminate.

This is still an internal interface, but the subscription mechanism
should probably be made external  (eg. a diameter:subscribe/1 that can
be used to subscribe to specified messages), so that transport modules
other than diameter's own can make use of it. There is no support for
soft upgrade.

2 files changed, 24 insertions, 44 deletions

diff --git a/lib/diameter/src/transport/diameter_sctp.erl b/lib/diameter/src/transport/diameter_sctp.erl
index 8a80ce630a..4a005b853d 100644
--- a/lib/diameter/src/transport/diameter_sctp.erl
+++ b/lib/diameter/src/transport/diameter_sctp.erl
@@ -1,7 +1,7 @@
 %%
 %% %CopyrightBegin%
 %%
-%% Copyright Ericsson AB 2010-2015. All Rights Reserved.
+%% Copyright Ericsson AB 2010-2016. All Rights Reserved.
 %%
 %% Licensed under the Apache License, Version 2.0 (the "License");
 %% you may not use this file except in compliance with the License.
@@ -61,10 +61,6 @@
 %% Remote addresses to accept connections from.
 -define(DEFAULT_ACCEPT, []).  %% any
 
-%% How long a listener with no associations lives before offing
-%% itself.
--define(LISTENER_TIMEOUT, 30000).
-
 %% How long to wait for a transport process to attach after
 %% association establishment.
 -define(ACCEPT_TIMEOUT, 5000).
@@ -104,7 +100,6 @@
          socket    :: gen_sctp:sctp_socket(),
          count = 0 :: uint(),  %% attached transport processes
          pending = {0, queue:new()},
-         tref      :: reference() | undefined,
          accept    :: [match()]}).
 %% Field pending implements two queues: the first of transport-to-be
 %% processes to which an association has been assigned but for which
@@ -216,14 +211,15 @@ init(T) ->
 
 %% A process owning a listening socket.
 i({listen, Ref, {Opts, Addrs}}) ->
+    [_] = diameter_config:subscribe(Ref, transport), %% assert existence
     {[Matches], Rest} = proplists:split(Opts, [accept]),
     {LAs, Sock} = AS = open(Addrs, Rest, ?DEFAULT_PORT),
     ok = gen_sctp:listen(Sock, true),
     true = diameter_reg:add_new({?MODULE, listener, {Ref, AS}}),
     proc_lib:init_ack({ok, self(), LAs}),
-    start_timer(#listener{ref = Ref,
-                          socket = Sock,
-                          accept = [[M] || {accept, M} <- Matches]});
+    #listener{ref = Ref,
+              socket = Sock,
+              accept = [[M] || {accept, M} <- Matches]};
 
 %% A connecting transport.
 i({connect, Pid, Opts, Addrs, Ref}) ->
@@ -431,13 +427,6 @@ putr(Key, Val) ->
 getr(Key) ->
     get({?MODULE, Key}).
 
-%% start_timer/1
-
-start_timer(#listener{count = 0} = S) ->
-    S#listener{tref = erlang:start_timer(?LISTENER_TIMEOUT, self(), close)};
-start_timer(S) ->
-    S.
-
 %% l/2
 %%
 %% Transition listener state.
@@ -455,12 +444,10 @@ l({sctp, Sock, _RA, _RP, Data} = T, #listener{socket = Sock,
 l({'DOWN', _MRef, process, TPid, _}, #listener{pending = {_,Q}} = S) ->
     down(queue:member(TPid, Q), TPid, S);
 
-%% Timeout after the last accepting process has died.
-l({timeout, TRef, close = T}, #listener{tref = TRef,
-                                        count = 0}) ->
-    x(T);
-l({timeout, _, close}, #listener{} = S) ->
-    S.
+%% Transport has been removed.
+l({transport, remove, _} = T, #listener{socket = Sock}) ->
+    gen_sctp:close(Sock),
+    x(T).
 
 %% down/3
 %%
@@ -472,15 +459,15 @@ down(true, TPid, #listener{pending = {N,Q},
                  = S) ->
     NQ = queue:filter(fun(P) -> P /= TPid end, Q),
     if N < 0 ->  %% awaiting an association ...
-            start_timer(S#listener{count = K-1,
-                                   pending = {N+1, NQ}});
+            S#listener{count = K-1,
+                       pending = {N+1, NQ}};
        true ->   %% ... or one has been assigned
             S#listener{pending = {N-1, NQ}}
     end;
 
 %% ... or one that's already attached.
 down(false, _TPid, #listener{count = K} = S) ->
-    start_timer(S#listener{count = K-1}).
+    S#listener{count = K-1}.
 
 %% t/2
 %%
diff --git a/lib/diameter/src/transport/diameter_tcp.erl b/lib/diameter/src/transport/diameter_tcp.erl
index 6a5e5fe89d..546c2cfa5e 100644
--- a/lib/diameter/src/transport/diameter_tcp.erl
+++ b/lib/diameter/src/transport/diameter_tcp.erl
@@ -57,7 +57,6 @@
 -define(ERROR(T), erlang:error({T, ?MODULE, ?LINE})).
 
 -define(DEFAULT_PORT, 3868).  %% RFC 3588, ch 2.1
--define(LISTENER_TIMEOUT, 30000).
 -define(DEFAULT_FRAGMENT_TIMEOUT, 1000).
 
 -define(IS_UINT32(N), (is_integer(N) andalso 0 =< N andalso 0 == N bsr 32)).
@@ -73,8 +72,10 @@
 
 %% Listener process state.
 -record(listener, {socket    :: inet:socket(),
-                   count = 1 :: non_neg_integer(),
-                   tref      :: reference() | undefined}).
+                   count = 1 :: non_neg_integer()}).  %% accepting processes
+%% The count of accepting processes was previously used to terminate
+%% the listening process, but diameter_reg:subscribe/2 is now used for
+%% this. Leave the the count for trace purposes.
 
 %% Monitor process state.
 -record(monitor,
@@ -240,6 +241,7 @@ i(#monitor{parent = Pid, transport = TPid} = S) ->
 %% gen_tcp seems to so. Links should be left to supervisors.
 
 i({listen, LRef, APid, {Mod, Opts, Addrs}}) ->
+    [_] = diameter_config:subscribe(LRef, transport), %% assert existence
     {[LA, LP], Rest} = proplists:split(Opts, [ip, port]),
     LAddrOpt = get_addr(LA, Addrs),
     LPort = get_port(LP),
@@ -248,7 +250,7 @@ i({listen, LRef, APid, {Mod, Opts, Addrs}}) ->
     true = diameter_reg:add_new({?MODULE, listener, {LRef, {LAddr, LSock}}}),
     proc_lib:init_ack({ok, self(), {LAddr, LSock}}),
     monitor(process, APid),
-    start_timer(#listener{socket = LSock}).
+    #listener{socket = LSock}.
 
 laddr([], Mod, Sock) ->
     {ok, {Addr, _Port}} = sockname(Mod, Sock),
@@ -484,13 +486,6 @@ putr(Key, Val) ->
 getr(Key) ->
     get({?MODULE, Key}).
 
-%% start_timer/1
-
-start_timer(#listener{count = 0} = S) ->
-    S#listener{tref = erlang:start_timer(?LISTENER_TIMEOUT, self(), close)};
-start_timer(S) ->
-    S.
-
 %% m/2
 %%
 %% Transition monitor state.
@@ -512,21 +507,19 @@ m({'DOWN', _, process, Pid, _}, #monitor{parent = Pid,
 %%
 %% Transition listener state.
 
-%% Another accept transport is attaching.
+%% An accepting transport is attaching.
 l({accept, TPid}, #listener{count = N} = S) ->
     monitor(process, TPid),
     S#listener{count = N+1};
 
 %% Accepting process has died.
 l({'DOWN', _, process, _, _}, #listener{count = N} = S) ->
-    start_timer(S#listener{count = N-1});
+    S#listener{count = N-1};
 
-%% Timeout after the last accepting process has died.
-l({timeout, TRef, close = T}, #listener{tref = TRef,
-                                        count = 0}) ->
-    x(T);
-l({timeout, _, close}, #listener{} = S) ->
-    S.
+%% Transport has been removed.
+l({transport, remove, _} = T, #listener{socket = Sock}) ->
+    gen_tcp:close(Sock),
+    x(T).
 
 %% t/2
 %%