Add the option { hibernate_after, int() } to ssl:connect and ssl:listen

When making an SSL connection (either as client or as server), the
process implementing the connection may use as much as hundreds of
kilobytes of memory, even when idle. This is problematic for any
application maintaining more than just a few SSL connections.

This patch introduces the option { hibernate_after, int() } to the
ssl:connect and ssl:listen functions, making the SSL connection
process go into hibernation after the specified number of milliseconds
of inactivity. This will reduce the memory used by the process to
just a few hundred bytes, making applications with thousands or
more SSL connections feasible, as long as most of the connections
are idle for most of the time (which is typically the case).

The approach of making the process go into hibernation only after
some time of inactivity was chosen because hibernation incurs some
CPU usage, and it is therefore not desirable for a process to
hibernate after each call.

3 files changed, 70 insertions, 35 deletions

diff --git a/lib/ssl/src/ssl.erl b/lib/ssl/src/ssl.erl
index b85188b878..3512e194bc 100644
--- a/lib/ssl/src/ssl.erl
+++ b/lib/ssl/src/ssl.erl
@@ -60,7 +60,7 @@
                         {keyfile, path()} | {password, string()} | {cacerts, [der_encoded()]} |
                         {cacertfile, path()} | {dh, der_encoded()} | {dhfile, path()} |
                         {ciphers, ciphers()} | {ssl_imp, ssl_imp()} | {reuse_sessions, boolean()} |
-                        {reuse_session, fun()}.
+                        {reuse_session, fun()} | {hibernate_after, integer()|undefined}.
 
 -type verify_type()  :: verify_none | verify_peer.
 -type path()         :: string().
@@ -711,7 +711,8 @@ handle_options(Opts0, _Role) ->
       reuse_sessions = handle_option(reuse_sessions, Opts, true),
       secure_renegotiate = handle_option(secure_renegotiate, Opts, false),
       renegotiate_at = handle_option(renegotiate_at, Opts, ?DEFAULT_RENEGOTIATE_AT),
-      debug      = handle_option(debug, Opts, [])
+      debug      = handle_option(debug, Opts, []),
+      hibernate_after = handle_option(hibernate_after, Opts, undefined)
      },
 
     CbInfo  = proplists:get_value(cb_info, Opts, {gen_tcp, tcp, tcp_closed, tcp_error}),    
@@ -720,7 +721,7 @@ handle_options(Opts0, _Role) ->
 		  depth, cert, certfile, key, keyfile,
 		  password, cacerts, cacertfile, dh, dhfile, ciphers,
 		  debug, reuse_session, reuse_sessions, ssl_imp,
-		  cb_info, renegotiate_at, secure_renegotiate],
+		  cb_info, renegotiate_at, secure_renegotiate, hibernate_after],
     
     SockOpts = lists:foldl(fun(Key, PropList) -> 
 				   proplists:delete(Key, PropList)
@@ -827,6 +828,10 @@ validate_option(renegotiate_at, Value) when is_integer(Value) ->
 
 validate_option(debug, Value) when is_list(Value); Value == true ->
     Value;
+validate_option(hibernate_after, undefined) ->
+    undefined;
+validate_option(hibernate_after, Value) when is_integer(Value), Value >= 0 ->
+    Value;
 validate_option(Opt, Value) ->
     throw({error, {eoptions, {Opt, Value}}}).
     
diff --git a/lib/ssl/src/ssl_connection.erl b/lib/ssl/src/ssl_connection.erl
index 85245f4342..574e1e9468 100644
--- a/lib/ssl/src/ssl_connection.erl
+++ b/lib/ssl/src/ssl_connection.erl
@@ -289,9 +289,9 @@ start_link(Role, Host, Port, Socket, Options, User, CbInfo) ->
 %% gen_fsm callbacks
 %%====================================================================
 %%--------------------------------------------------------------------
--spec init(list()) -> {ok, state_name(), #state{}} | {stop, term()}.                   
+-spec init(list()) -> {ok, state_name(), #state{}, timeout()} | {stop, term()}.
 %% Possible return values not used now.
-%%			  | {ok, state_name(), #state{}, timeout()} |
+%%			  | {ok, state_name(), #state{}} |
 %%			  ignore  
 %% Description:Whenever a gen_fsm is started using gen_fsm:start/[3,4] or
 %% gen_fsm:start_link/3,4, this function is called by the new process to 
@@ -311,7 +311,7 @@ init([Role, Host, Port, Socket, {SSLOpts0, _} = Options,
 				 session_cache = CacheRef,
 				 private_key = Key,
 				 diffie_hellman_params = DHParams},
-	    {ok, hello, State}
+	    {ok, hello, State, get_timeout(State)}
     catch   
 	throw:Error ->
 	    {stop, Error}
@@ -412,6 +412,9 @@ hello(Hello = #client_hello{client_version = ClientVersion},
             {stop, normal, State}
     end;
 
+hello(timeout, State) ->
+    { next_state, hello, State, hibernate };
+
 hello(Msg, State) ->
     handle_unexpected_message(Msg, hello, State).
 %%--------------------------------------------------------------------
@@ -460,6 +463,9 @@ abbreviated(#finished{verify_data = Data} = Finished,
             {stop, normal, State} 
     end;
 
+abbreviated(timeout, State) ->
+    { next_state, abbreviated, State, hibernate };
+
 abbreviated(Msg, State) ->
     handle_unexpected_message(Msg, abbreviated, State).
 
@@ -582,6 +588,9 @@ certify(#client_key_exchange{exchange_keys = Keys},
 	    {stop, normal, State}
     end;
 
+certify(timeout, State) ->
+    { next_state, certify, State, hibernate };
+
 certify(Msg, State) ->
     handle_unexpected_message(Msg, certify, State).
 
@@ -664,6 +673,9 @@ cipher(#finished{verify_data = Data} = Finished,
             {stop, normal, State} 
     end;
 
+cipher(timeout, State) ->
+    { next_state, cipher, State, hibernate };
+
 cipher(Msg, State) ->
     handle_unexpected_message(Msg, cipher, State).
 
@@ -693,6 +705,9 @@ connection(#hello_request{}, #state{host = Host, port = Port,
 connection(#client_hello{} = Hello, #state{role = server} = State) ->
     hello(Hello, State);
 
+connection(timeout, State) ->
+    {next_state, connection, State, hibernate};
+
 connection(Msg, State) ->
     handle_unexpected_message(Msg, connection, State).
 %%--------------------------------------------------------------------
@@ -705,7 +720,7 @@ connection(Msg, State) ->
 %% the event. Not currently used!
 %%--------------------------------------------------------------------
 handle_event(_Event, StateName, State) ->
-    {next_state, StateName, State}.
+    {next_state, StateName, State, get_timeout(State)}.
 
 %%--------------------------------------------------------------------
 -spec handle_sync_event(term(), from(), state_name(), #state{}) -> 
@@ -736,7 +751,8 @@ handle_sync_event({application_data, Data0}, From, connection,
 	    {Msgs, [], ConnectionStates} ->
 		Result = Transport:send(Socket, Msgs),
 		{reply, Result,
-		 connection, State#state{connection_states = ConnectionStates}};
+		 connection, State#state{connection_states = ConnectionStates},
+                 get_timeout(State)};
 	    {Msgs, RestData, ConnectionStates} ->
 		if 
 		    Msgs =/= [] ->
@@ -749,12 +765,14 @@ handle_sync_event({application_data, Data0}, From, connection,
 					renegotiation = {true, internal}})
 	end
     catch throw:Error ->
-	    {reply, Error, connection, State}
+	    {reply, Error, connection, State, get_timeout(State)}
     end;
 handle_sync_event({application_data, Data}, From, StateName, 
 		  #state{send_queue = Queue} = State) ->
     %% In renegotiation priorities handshake, send data when handshake is finished
-    {next_state, StateName, State#state{send_queue = queue:in({From, Data}, Queue)}};
+    {next_state, StateName,
+     State#state{send_queue = queue:in({From, Data}, Queue)},
+     get_timeout(State)};
 
 handle_sync_event(start, From, hello, State) ->
     hello(start, State#state{from = From});
@@ -768,9 +786,9 @@ handle_sync_event(start, From, hello, State) ->
 %% here to make sure it is the users problem and not owers if
 %% they upgrade a active socket. 
 handle_sync_event(start, _, connection, State) ->
-    {reply, connected, connection, State};
+    {reply, connected, connection, State, get_timeout(State)};
 handle_sync_event(start, From, StateName, State) ->
-    {next_state, StateName, State#state{from = From}};
+    {next_state, StateName, State#state{from = From}, get_timeout(State)};
 
 handle_sync_event(close, _, StateName, State) ->
     %% Run terminate before returning
@@ -796,7 +814,7 @@ handle_sync_event({shutdown, How0}, _, StateName,
     
     case Transport:shutdown(Socket, How0) of
 	ok ->
-	    {reply, ok, StateName, State};
+	    {reply, ok, StateName, State, get_timeout(State)};
 	Error ->
 	    {stop, normal, Error, State}
     end;
@@ -807,30 +825,33 @@ handle_sync_event({recv, N}, From, connection = StateName, State0) ->
 %% Doing renegotiate wait with handling request until renegotiate is
 %% finished. Will be handled by next_state_connection/2.
 handle_sync_event({recv, N}, From, StateName, State) ->
-    {next_state, StateName, State#state{bytes_to_read = N, from = From,
-				       recv_during_renegotiation = true}};
+    {next_state, StateName,
+     State#state{bytes_to_read = N, from = From,
+                 recv_during_renegotiation = true},
+     get_timeout(State)};
 
 handle_sync_event({new_user, User}, _From, StateName, 
 		  State =#state{user_application = {OldMon, _}}) ->
     NewMon = erlang:monitor(process, User),
     erlang:demonitor(OldMon, [flush]),
-    {reply, ok, StateName, State#state{user_application = {NewMon,User}}};
+    {reply, ok, StateName, State#state{user_application = {NewMon,User}},
+     get_timeout(State)};
 
 handle_sync_event({get_opts, OptTags}, _From, StateName,
 		  #state{socket = Socket,
 			 socket_options = SockOpts} = State) ->
     OptsReply = get_socket_opts(Socket, OptTags, SockOpts, []),
-    {reply, OptsReply, StateName, State};
+    {reply, OptsReply, StateName, State, get_timeout(State)};
 
 handle_sync_event(sockname, _From, StateName,
 		  #state{socket = Socket} = State) ->
     SockNameReply = inet:sockname(Socket),
-    {reply, SockNameReply, StateName, State};
+    {reply, SockNameReply, StateName, State, get_timeout(State)};
 
 handle_sync_event(peername, _From, StateName,
 		  #state{socket = Socket} = State) ->
     PeerNameReply = inet:peername(Socket),
-    {reply, PeerNameReply, StateName, State};
+    {reply, PeerNameReply, StateName, State, get_timeout(State)};
 
 handle_sync_event({set_opts, Opts0}, _From, StateName, 
 		  #state{socket_options = Opts1, 
@@ -840,27 +861,27 @@ handle_sync_event({set_opts, Opts0}, _From, StateName,
     State1 = State0#state{socket_options = Opts},
     if 
 	Opts#socket_options.active =:= false ->
-	    {reply, ok, StateName, State1};
+	    {reply, ok, StateName, State1, get_timeout(State1)};
 	Buffer =:= <<>>, Opts1#socket_options.active =:= false ->
             %% Need data, set active once
 	    {Record, State2} = next_record_if_active(State1),
 	    case next_state(StateName, Record, State2) of
-		{next_state, StateName, State} ->
-		    {reply, ok, StateName, State};
+		{next_state, StateName, State, Timeout} ->
+		    {reply, ok, StateName, State, Timeout};
 		{stop, Reason, State} ->
 		    {stop, Reason, State}
 	    end;
 	Buffer =:= <<>> ->
             %% Active once already set 
-	    {reply, ok, StateName, State1};
+	    {reply, ok, StateName, State1, get_timeout(State1)};
 	true ->
 	    case application_data(<<>>, State1) of
 		Stop = {stop,_,_} ->
 		    Stop;
 		{Record, State2} ->
 		    case next_state(StateName, Record, State2) of
-			{next_state, StateName, State} ->
-			    {reply, ok, StateName, State};
+			{next_state, StateName, State, Timeout} ->
+			    {reply, ok, StateName, State, Timeout};
 			{stop, Reason, State} ->
 			    {stop, Reason, State}
 		    end
@@ -871,7 +892,7 @@ handle_sync_event(renegotiate, From, connection, State) ->
     renegotiate(State#state{renegotiation = {true, From}});
 
 handle_sync_event(renegotiate, _, StateName, State) ->
-    {reply, {error, already_renegotiating}, StateName, State};
+    {reply, {error, already_renegotiating}, StateName, State, get_timeout(State)};
 
 handle_sync_event(info, _, StateName, 
 		  #state{negotiated_version = Version,
@@ -879,19 +900,19 @@ handle_sync_event(info, _, StateName,
     
     AtomVersion = ssl_record:protocol_version(Version),
     {reply, {ok, {AtomVersion, ssl_cipher:suite_definition(Suite)}}, 
-     StateName, State};
+     StateName, State, get_timeout(State)};
 
 handle_sync_event(session_info, _, StateName, 
 		  #state{session = #session{session_id = Id,
 					    cipher_suite = Suite}} = State) ->
     {reply, [{session_id, Id}, 
 	     {cipher_suite, ssl_cipher:suite_definition(Suite)}], 
-     StateName, State};
+     StateName, State, get_timeout(State)};
 
 handle_sync_event(peer_certificate, _, StateName, 
 		  #state{session = #session{peer_certificate = Cert}} 
 		  = State) ->
-    {reply, {ok, Cert}, StateName, State}.
+    {reply, {ok, Cert}, StateName, State, get_timeout(State)}.
 
 %%--------------------------------------------------------------------
 -spec handle_info(msg(),state_name(), #state{}) -> 
@@ -955,7 +976,7 @@ handle_info({'DOWN', MonitorRef, _, _, _}, _,
 handle_info(Msg, StateName, State) ->
     Report = io_lib:format("SSL: Got unexpected info: ~p ~n", [Msg]),
     error_logger:info_report(Report),
-    {next_state, StateName, State}.
+    {next_state, StateName, State, get_timeout(State)}.
 
 %%--------------------------------------------------------------------
 -spec terminate(reason(), state_name(), #state{}) -> term().
@@ -1778,7 +1799,7 @@ handle_tls_handshake(Handle, StateName, #state{tls_packets = [Packet]} = State)
 handle_tls_handshake(Handle, StateName, #state{tls_packets = [Packet | Packets]} = State0) ->
     FsmReturn = {next_state, StateName, State0#state{tls_packets = Packets}},
     case Handle(Packet, FsmReturn) of
-	{next_state, NextStateName, State} ->
+	{next_state, NextStateName, State, _Timeout} ->
 	    handle_tls_handshake(Handle, NextStateName, State);
 	{stop, _,_} = Stop ->
 	    Stop
@@ -1789,11 +1810,11 @@ next_state(_, #alert{} = Alert, #state{negotiated_version = Version} = State) ->
     {stop, normal, State};
 
 next_state(Next, no_record, State) ->
-    {next_state, Next, State};
+    {next_state, Next, State, get_timeout(State)};
 
 next_state(Next, #ssl_tls{type = ?ALERT, fragment = EncAlerts}, State) ->
     Alerts = decode_alerts(EncAlerts),
-    handle_alerts(Alerts,  {next_state, Next, State});
+    handle_alerts(Alerts,  {next_state, Next, State, get_timeout(State)});
 
 next_state(StateName, #ssl_tls{type = ?HANDSHAKE, fragment = Data},
 	   State0 = #state{tls_handshake_buffer = Buf0, negotiated_version = Version}) ->
@@ -2044,7 +2065,7 @@ handle_alerts([], Result) ->
 handle_alerts(_, {stop, _, _} = Stop) ->
     %% If it is a fatal alert immediately close 
     Stop;
-handle_alerts([Alert | Alerts], {next_state, StateName, State}) ->
+handle_alerts([Alert | Alerts], {next_state, StateName, State, _Timeout}) ->
     handle_alerts(Alerts, handle_alert(Alert, StateName, State)).
 
 handle_alert(#alert{level = ?FATAL} = Alert, StateName,
@@ -2225,3 +2246,8 @@ linux_workaround_transport_delivery_problems(#alert{level = ?FATAL}, Socket) ->
     end;
 linux_workaround_transport_delivery_problems(_, _) ->
     ok.
+
+get_timeout(#state{ssl_options=#ssl_options{hibernate_after=undefined}}) ->
+    infinity;
+get_timeout(#state{ssl_options=#ssl_options{hibernate_after=HibernateAfter}}) ->
+    HibernateAfter.
diff --git a/lib/ssl/src/ssl_internal.hrl b/lib/ssl/src/ssl_internal.hrl
index 715941e3ad..c28daa271e 100644
--- a/lib/ssl/src/ssl_internal.hrl
+++ b/lib/ssl/src/ssl_internal.hrl
@@ -98,7 +98,11 @@
 	  reuse_sessions, % boolean()
 	  renegotiate_at,
 	  secure_renegotiate,
-	  debug           %
+	  debug,
+	  hibernate_after % undefined if not hibernating,
+                          % or number of ms of inactivity
+			  % after which ssl_connection will
+                          % go into hibernation
 	  }).
 
 -record(socket_options,