aboutsummaryrefslogtreecommitdiffstats
path: root/lib/kernel/src/dist_util.erl
blob: b1d32322e3f6619dd9e9189a2b200b9645183422 (plain) (blame)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
%%
%% %CopyrightBegin%
%%
%% Copyright Ericsson AB 1999-2010. All Rights Reserved.
%%
%% The contents of this file are subject to the Erlang Public License,
%% Version 1.1, (the "License"); you may not use this file except in
%% compliance with the License. You should have received a copy of the
%% Erlang Public License along with this software. If not, it can be
%% retrieved online at http://www.erlang.org/.
%%
%% Software distributed under the License is distributed on an "AS IS"
%% basis, WITHOUT WARRANTY OF ANY KIND, either express or implied. See
%% the License for the specific language governing rights and limitations
%% under the License.
%%
%% %CopyrightEnd%
%%
%%%----------------------------------------------------------------------
%%% Purpose : The handshake of a streamed distribution connection
%%%           in a separate file to make it usable for other
%%%           distribution protocols.
%%%----------------------------------------------------------------------

-module(dist_util).

%%-compile(export_all).
-export([handshake_we_started/1, handshake_other_started/1,
	 start_timer/1, setup_timer/2, 
	 reset_timer/1, cancel_timer/1,
	 shutdown/3, shutdown/4]).

-import(error_logger,[error_msg/2]).

-include("dist_util.hrl").
-include("dist.hrl").

-ifdef(DEBUG).
-define(shutdown_trace(A,B), io:format(A,B)).
-else.
-define(shutdown_trace(A,B), noop).
-endif.

-define(to_port(FSend, Socket, Data),
	case FSend(Socket, Data) of
	    {error, closed} ->
		self() ! {tcp_closed, Socket},
	        {error, closed};
	    R ->
	        R
        end).


-define(int16(X), [((X) bsr 8) band 16#ff, (X) band 16#ff]).

-define(int32(X), 
	[((X) bsr 24) band 16#ff, ((X) bsr 16) band 16#ff,
	 ((X) bsr 8) band 16#ff, (X) band 16#ff]).

-define(i16(X1,X0),
        (?u16(X1,X0) - 
         (if (X1) > 127 -> 16#10000; true -> 0 end))).

-define(u16(X1,X0),
        (((X1) bsl 8) bor (X0))).

-define(u32(X3,X2,X1,X0),
        (((X3) bsl 24) bor ((X2) bsl 16) bor ((X1) bsl 8) bor (X0))).

-record(tick, {read = 0,
	       write = 0,
	       tick = 0,
	       ticked = 0
	       }).

remove_flag(Flag, Flags) ->
    case Flags band Flag of
	0 ->
	    Flags;
	_ ->
	    Flags - Flag
    end.

adjust_flags(ThisFlags, OtherFlags) ->
    case (?DFLAG_PUBLISHED band ThisFlags) band OtherFlags of
	0 ->
	    {remove_flag(?DFLAG_PUBLISHED, ThisFlags),
	     remove_flag(?DFLAG_PUBLISHED, OtherFlags)};
	_ ->
	    {ThisFlags, OtherFlags}
    end.

publish_flag(hidden, _) ->
    0;
publish_flag(_, OtherNode) ->
    case net_kernel:publish_on_node(OtherNode) of
	true ->
	    ?DFLAG_PUBLISHED;
	_ ->
	    0
    end.

make_this_flags(RequestType, OtherNode) ->
    publish_flag(RequestType, OtherNode) bor
	%% The parenthesis below makes the compiler generate better code.
	(?DFLAG_EXPORT_PTR_TAG bor
	 ?DFLAG_EXTENDED_PIDS_PORTS bor
	 ?DFLAG_EXTENDED_REFERENCES bor
	 ?DFLAG_DIST_MONITOR bor
	 ?DFLAG_FUN_TAGS bor
	 ?DFLAG_DIST_MONITOR_NAME bor
	 ?DFLAG_HIDDEN_ATOM_CACHE bor
	 ?DFLAG_NEW_FUN_TAGS bor
	 ?DFLAG_BIT_BINARIES bor
	 ?DFLAG_NEW_FLOATS bor
	 ?DFLAG_UNICODE_IO bor
	 ?DFLAG_DIST_HDR_ATOM_CACHE bor
	 ?DFLAG_SMALL_ATOM_TAGS bor
	 ?DFLAG_UTF8_ATOMS).

handshake_other_started(#hs_data{request_type=ReqType}=HSData0) ->
    {PreOtherFlags,Node,Version} = recv_name(HSData0),
    PreThisFlags = make_this_flags(ReqType, Node),
    {ThisFlags, OtherFlags} = adjust_flags(PreThisFlags,
					   PreOtherFlags),
    HSData = HSData0#hs_data{this_flags=ThisFlags,
			     other_flags=OtherFlags,
			     other_version=Version,
			     other_node=Node,
			     other_started=true},
    check_dflag_xnc(HSData),
    is_allowed(HSData),
    ?debug({"MD5 connection from ~p (V~p)~n",
	    [Node, HSData#hs_data.other_version]}),
    mark_pending(HSData),
    {MyCookie,HisCookie} = get_cookies(Node),
    ChallengeA = gen_challenge(),
    send_challenge(HSData, ChallengeA),
    reset_timer(HSData#hs_data.timer),
    ChallengeB = recv_challenge_reply(HSData, ChallengeA, MyCookie),
    send_challenge_ack(HSData, gen_digest(ChallengeB, HisCookie)),
    ?debug({dist_util, self(), accept_connection, Node}),
    connection(HSData).

%%
%% check if connecting node is allowed to connect
%% with allow-node-scheme
%%
is_allowed(#hs_data{other_node = Node, 
		    allowed = Allowed} = HSData) ->
    case lists:member(Node, Allowed) of
	false when Allowed =/= [] ->
	    send_status(HSData, not_allowed),
	    error_msg("** Connection attempt from "
		      "disallowed node ~w ** ~n", [Node]),
	    ?shutdown(Node);
	_ -> true
    end.

%%
%% Check that both nodes can handle the same types of extended
%% node containers. If they can not, abort the connection.
%%
check_dflag_xnc(#hs_data{other_node = Node,
			 other_flags = OtherFlags,
			 other_started = OtherStarted} = HSData) ->
    XRFlg = ?DFLAG_EXTENDED_REFERENCES,
    XPPFlg = case erlang:system_info(compat_rel) of
		 R when R >= 10 ->
		     ?DFLAG_EXTENDED_PIDS_PORTS;
		 _ ->
		     0
	     end,
    ReqXncFlags = XRFlg bor XPPFlg,
    case OtherFlags band ReqXncFlags =:= ReqXncFlags of
	true ->
	    ok;
	false ->
	    What = case {OtherFlags band XRFlg =:= XRFlg,
			 OtherFlags band XPPFlg =:= XPPFlg} of
		       {false, false} -> "references, pids and ports";
		       {true, false} -> "pids and ports";
		       {false, true} -> "references"
		   end,
	    case OtherStarted of
		true ->
		    send_status(HSData, not_allowed),
		    Dir = "from",
		    How = "rejected";
	        _ ->
		    Dir = "to",
		    How = "aborted"
	    end,
	    error_msg("** ~w: Connection attempt ~s node ~w ~s "
		      "since it cannot handle extended ~s. "
		      "**~n", [node(), Dir, Node, How, What]),
	    ?shutdown(Node)
    end.


%% No nodedown will be sent if we fail before this process has
%% succeeded to mark the node as pending.

mark_pending(#hs_data{kernel_pid=Kernel,
		      other_node=Node,
		      this_node=MyNode}=HSData) ->
    case do_mark_pending(Kernel, MyNode, Node,
			 (HSData#hs_data.f_address)(HSData#hs_data.socket,
						    Node),
			 HSData#hs_data.other_flags) of
	ok ->
	    send_status(HSData, ok),
	    reset_timer(HSData#hs_data.timer);

	ok_pending ->
	    send_status(HSData, ok_simultaneous),
	    reset_timer(HSData#hs_data.timer);

	nok_pending ->
	    send_status(HSData, nok),
	    ?shutdown(Node);
	    
	up_pending ->
	    %% Check if connection is still alive, no
	    %% implies that the connection is no longer pending
	    %% due to simultaneous connect
	    do_alive(HSData),

	    %% This can happen if the other node goes down,
	    %% and goes up again and contact us before we have
	    %% detected that the socket was closed. 
	    wait_pending(Kernel),
	    reset_timer(HSData#hs_data.timer);

	already_pending ->
	    %% FIXME: is this a case ?
	    ?debug({dist_util,self(),mark_pending,already_pending,Node}),
	    ?shutdown(Node)
    end.


%%
%% Marking pending and negotiating away 
%% simultaneous connection problems
%%

wait_pending(Kernel) ->
    receive
	{Kernel, pending} ->
	    ?trace("wait_pending returned for pid ~p.~n", 
		   [self()]),
	    ok
    end.

do_alive(#hs_data{other_node = Node} = HSData) ->
    send_status(HSData, alive),
    case recv_status(HSData) of
	true  -> true;
	false -> ?shutdown(Node)
    end.
    
do_mark_pending(Kernel, MyNode, Node, Address, Flags) ->
    Kernel ! {self(), {accept_pending,MyNode,Node,Address,
		       publish_type(Flags)}},
    receive
	{Kernel,{accept_pending,Ret}} ->
	    ?trace("do_mark_pending(~p,~p,~p,~p) -> ~p~n",
		   [Kernel,Node,Address,Flags,Ret]),
	    Ret
    end.

is_pending(Kernel, Node) ->
    Kernel ! {self(), {is_pending, Node}},
    receive
	{Kernel, {is_pending, Reply}} -> Reply
    end.
    
%%
%% This will tell the net_kernel about the nodedown as it
%% recognizes the exit signal.
%% The termination of this process does also imply that the Socket
%% is closed in a controlled way by inet_drv.
%%

-spec shutdown(atom(), non_neg_integer(), term()) -> no_return().

shutdown(Module, Line, Data) ->
    shutdown(Module, Line, Data, shutdown).

-spec shutdown(atom(), non_neg_integer(), term(), term()) -> no_return().

shutdown(_Module, _Line, _Data, Reason) ->
    ?shutdown_trace("Net Kernel 2: shutting down connection "
		    "~p:~p, data ~p,reason ~p~n",
		    [_Module,_Line, _Data, Reason]),
    flush_down(),
    exit(Reason).
%% Use this line to debug connection.  
%% Set net_kernel verbose = 1 as well.
%%    exit({Reason, ?MODULE, _Line, _Data, erlang:now()}).


flush_down() ->
    receive
	{From, get_status} ->
	    From ! {self(), get_status, error},
	    flush_down()
    after 0 ->
	    ok
    end.

handshake_we_started(#hs_data{request_type=ReqType,
			      other_node=Node}=PreHSData) ->
    PreThisFlags = make_this_flags(ReqType, Node),
    HSData = PreHSData#hs_data{this_flags=PreThisFlags},
    send_name(HSData),
    recv_status(HSData),
    {PreOtherFlags,ChallengeA} = recv_challenge(HSData),
    {ThisFlags,OtherFlags} = adjust_flags(PreThisFlags, PreOtherFlags),
    NewHSData = HSData#hs_data{this_flags = ThisFlags,
			       other_flags = OtherFlags, 
			       other_started = false}, 
    check_dflag_xnc(NewHSData),
    MyChallenge = gen_challenge(),
    {MyCookie,HisCookie} = get_cookies(Node),
    send_challenge_reply(NewHSData,MyChallenge,
			 gen_digest(ChallengeA,HisCookie)),
    reset_timer(NewHSData#hs_data.timer),
    recv_challenge_ack(NewHSData, MyChallenge, MyCookie),
    connection(NewHSData).

%% --------------------------------------------------------------
%% The connection has been established.
%% --------------------------------------------------------------

connection(#hs_data{other_node = Node,
		    socket = Socket,
		    f_address = FAddress,
		    f_setopts_pre_nodeup = FPreNodeup,
		    f_setopts_post_nodeup = FPostNodeup}= HSData) ->
    cancel_timer(HSData#hs_data.timer),
    PType = publish_type(HSData#hs_data.other_flags), 
    case FPreNodeup(Socket) of
	ok -> 
	    do_setnode(HSData), % Succeeds or exits the process.
	    Address = FAddress(Socket,Node),
	    mark_nodeup(HSData,Address),
	    case FPostNodeup(Socket) of
		ok ->
		    con_loop(HSData#hs_data.kernel_pid, 
			     Node, 
			     Socket, 
			     Address,
			     HSData#hs_data.this_node, 
			     PType,
			     #tick{},
			     HSData#hs_data.mf_tick,
			     HSData#hs_data.mf_getstat);
		_ ->
		    ?shutdown2(Node, connection_setup_failed)
	    end;
	_ ->
	    ?shutdown(Node)
    end.

%% Generate a message digest from Challenge number and Cookie	
gen_digest(Challenge, Cookie) when is_integer(Challenge), is_atom(Cookie) ->
    erlang:md5([atom_to_list(Cookie)|integer_to_list(Challenge)]).

%% ---------------------------------------------------------------
%% Challenge code
%% gen_challenge() returns a "random" number
%% ---------------------------------------------------------------
gen_challenge() ->
    {A,B,C} = erlang:now(),
    {D,_}   = erlang:statistics(reductions),
    {E,_}   = erlang:statistics(runtime),
    {F,_}   = erlang:statistics(wall_clock),
    {G,H,_} = erlang:statistics(garbage_collection),
    %% A(8) B(16) C(16)
    %% D(16),E(8), F(16) G(8) H(16)
    ( ((A bsl 24) + (E bsl 16) + (G bsl 8) + F) bxor
      (B + (C bsl 16)) bxor 
      (D + (H bsl 16)) ) band 16#ffffffff.

%%
%% Get the cookies for a node from auth
%%    
get_cookies(Node) ->
    case auth:get_cookie(Node) of
	X when is_atom(X) ->
	    {X,X}
%	{Y,Z} when is_atom(Y), is_atom(Z) ->
%	    {Y,Z};
%	_ ->
%	    erlang:error("Corrupt cookie database")
    end.    

%% No error return; either succeeds or terminates the process.
do_setnode(#hs_data{other_node = Node, socket = Socket, 
		    other_flags = Flags, other_version = Version,
		    f_getll = GetLL}) ->
    case GetLL(Socket) of
	{ok,Port} ->
	    ?trace("setnode(md5,~p ~p ~p)~n", 
		   [Node, Port, {publish_type(Flags), 
				 '(', Flags, ')', 
				 Version}]),
	    case (catch 
		  erlang:setnode(Node, Port, 
				 {Flags, Version, '', ''})) of
		{'EXIT', {system_limit, _}} ->
		    error_msg("** Distribution system limit reached, "
			      "no table space left for node ~w ** ~n",
			      [Node]),
		    ?shutdown(Node);
		{'EXIT', Other} ->
		    exit(Other);
		_Else ->
		    ok
	    end;
	_ ->
	    error_msg("** Distribution connection error, "
		      "could not get low level port for node ~w ** ~n",
		      [Node]),
	    ?shutdown(Node)
    end.

mark_nodeup(#hs_data{kernel_pid = Kernel, 
		     other_node = Node, 
		     other_flags = Flags,
		     other_started = OtherStarted}, 
	    Address) ->
    Kernel ! {self(), {nodeup,Node,Address,publish_type(Flags),
		       true}},
    receive
	{Kernel, inserted} ->
	    ok;
	{Kernel, bad_request} ->
	    TypeT = case OtherStarted of
		       true ->
			   "accepting connection";
		       _ ->
			   "initiating connection"
		   end,
	    error_msg("Fatal: ~p was not allowed to "
		      "send {nodeup, ~p} to kernel when ~s~n",
		      [self(), Node, TypeT]),
	    ?shutdown(Node)
    end.

con_loop(Kernel, Node, Socket, TcpAddress,
	 MyNode, Type, Tick, MFTick, MFGetstat) ->
    receive
	{tcp_closed, Socket} ->
	    ?shutdown2(Node, connection_closed);
	{Kernel, disconnect} ->
	    ?shutdown2(Node, disconnected);
	{Kernel, aux_tick} ->
	    case MFGetstat(Socket) of
		{ok, _, _, PendWrite} ->
		    send_tick(Socket, PendWrite, MFTick);
		_ ->
		    ignore_it
	    end,
	    con_loop(Kernel, Node, Socket, TcpAddress, MyNode, Type,
		     Tick, MFTick, MFGetstat);
	{Kernel, tick} ->
	    case send_tick(Socket, Tick, Type, 
			   MFTick, MFGetstat) of
		{ok, NewTick} ->
		    con_loop(Kernel, Node, Socket, TcpAddress,
			     MyNode, Type, NewTick, MFTick,  
			     MFGetstat);
		{error, not_responding} ->
 		    error_msg("** Node ~p not responding **~n"
 			      "** Removing (timedout) connection **~n",
 			      [Node]),
 		    ?shutdown2(Node, net_tick_timeout);
		_Other ->
		    ?shutdown2(Node, send_net_tick_failed)
	    end;
	{From, get_status} ->
	    case MFGetstat(Socket) of
		{ok, Read, Write, _} ->
		    From ! {self(), get_status, {ok, Read, Write}},
		    con_loop(Kernel, Node, Socket, TcpAddress, 
			     MyNode, 
			     Type, Tick, 
			     MFTick, MFGetstat);
		_ ->
		    ?shutdown2(Node, get_status_failed)
	    end
    end.


%% ------------------------------------------------------------
%% Misc. functions.
%% ------------------------------------------------------------

send_name(#hs_data{socket = Socket, this_node = Node, 
		   f_send = FSend, 
		   this_flags = Flags,
		   other_version = Version}) ->
    ?trace("send_name: node=~w, version=~w\n",
	   [Node,Version]),
    ?to_port(FSend, Socket, 
	     [$n, ?int16(Version), ?int32(Flags), atom_to_list(Node)]).

send_challenge(#hs_data{socket = Socket, this_node = Node, 
			other_version = Version, 
			this_flags = Flags,
			f_send = FSend},
	       Challenge ) ->
    ?trace("send: challenge=~w version=~w\n",
	   [Challenge,Version]),
    ?to_port(FSend, Socket, [$n,?int16(Version), ?int32(Flags),
			     ?int32(Challenge), 
			     atom_to_list(Node)]).

send_challenge_reply(#hs_data{socket = Socket, f_send = FSend}, 
		     Challenge, Digest) ->
    ?trace("send_reply: challenge=~w digest=~p\n",
	   [Challenge,Digest]),
    ?to_port(FSend, Socket, [$r,?int32(Challenge),Digest]).

send_challenge_ack(#hs_data{socket = Socket, f_send = FSend}, 
		   Digest) ->
    ?trace("send_ack: digest=~p\n", [Digest]),
    ?to_port(FSend, Socket, [$a,Digest]).


%%
%% Get the name of the other side.
%% Close the connection if invalid data.
%% The IP address sent is not interesting (as in the old
%% tcp_drv.c which used it to detect simultaneous connection
%% attempts).
%%
recv_name(#hs_data{socket = Socket, f_recv = Recv}) ->
    case Recv(Socket, 0, infinity) of
	{ok,Data} ->
	    get_name(Data);
	_ ->
	    ?shutdown(no_node)
    end.

get_name([$n,VersionA, VersionB, Flag1, Flag2, Flag3, Flag4 | OtherNode]) ->
    {?u32(Flag1, Flag2, Flag3, Flag4), list_to_atom(OtherNode), 
     ?u16(VersionA,VersionB)};
get_name(Data) ->
    ?shutdown(Data).

publish_type(Flags) ->
    case Flags band ?DFLAG_PUBLISHED of
	0 ->
	    hidden;
	_ ->
	    normal
    end.

%% wait for challenge after connect
recv_challenge(#hs_data{socket=Socket,other_node=Node,
			other_version=Version,f_recv=Recv}) ->
    case Recv(Socket, 0, infinity) of
	{ok,[$n,V1,V0,Fl1,Fl2,Fl3,Fl4,CA3,CA2,CA1,CA0 | Ns]} ->
	    Flags = ?u32(Fl1,Fl2,Fl3,Fl4),
	    try {list_to_existing_atom(Ns),?u16(V1,V0)} of
		{Node,Version} ->
		    Challenge = ?u32(CA3,CA2,CA1,CA0),
		    ?trace("recv: node=~w, challenge=~w version=~w\n",
			   [Node, Challenge,Version]),
		    {Flags,Challenge};
		_ ->
		    ?shutdown(no_node)
	    catch
		error:badarg ->
		    ?shutdown(no_node)
	    end;
	_ ->
	    ?shutdown(no_node)	    
    end.


%%
%% wait for challenge response after send_challenge
%%
recv_challenge_reply(#hs_data{socket = Socket, 
			      other_node = NodeB,
			      f_recv = FRecv}, 
		     ChallengeA, Cookie) ->
    case FRecv(Socket, 0, infinity) of
	{ok,[$r,CB3,CB2,CB1,CB0 | SumB]} when length(SumB) =:= 16 ->
	    SumA = gen_digest(ChallengeA, Cookie),
	    ChallengeB = ?u32(CB3,CB2,CB1,CB0),
	    ?trace("recv_reply: challenge=~w digest=~p\n",
		   [ChallengeB,SumB]),
	    ?trace("sum = ~p\n", [SumA]),
	    case list_to_binary(SumB) of
		SumA ->
		    ChallengeB;
		_ ->
		    error_msg("** Connection attempt from "
			      "disallowed node ~w ** ~n", [NodeB]),
		    ?shutdown(NodeB)
	    end;
	_ ->
	    ?shutdown(no_node)
    end.

recv_challenge_ack(#hs_data{socket = Socket, f_recv = FRecv, 
			    other_node = NodeB}, 
		   ChallengeB, CookieA) ->
    case FRecv(Socket, 0, infinity) of
	{ok,[$a|SumB]} when length(SumB) =:= 16 ->
	    SumA = gen_digest(ChallengeB, CookieA),
	    ?trace("recv_ack: digest=~p\n", [SumB]),
	    ?trace("sum = ~p\n", [SumA]),
	    case list_to_binary(SumB) of
		SumA ->
		    ok;
		_ ->
		    error_msg("** Connection attempt to "
			      "disallowed node ~w ** ~n", [NodeB]),
		    ?shutdown(NodeB)
	    end;
	_ ->
	    ?shutdown(NodeB)
    end.

recv_status(#hs_data{kernel_pid = Kernel, socket = Socket, 
		     other_node = Node, f_recv = Recv} = HSData) ->
    case Recv(Socket, 0, infinity) of
	{ok, [$s|StrStat]} ->
	    Stat = list_to_atom(StrStat),
	    ?debug({dist_util,self(),recv_status, Node, Stat}),
	    case Stat of
		not_allowed -> ?shutdown(Node);
		nok  -> 
		    %% wait to be killed by net_kernel
		    receive
		    after infinity -> ok
		    end;
		alive -> 
		    Reply = is_pending(Kernel, Node),
		    ?debug({is_pending,self(),Reply}),
		    send_status(HSData, Reply),
		    if not Reply ->
			    ?shutdown(Node);
		       Reply ->
			    Stat
		    end;
		_ -> Stat
	    end;
	_Error ->
	    ?debug({dist_util,self(),recv_status_error, 
		Node, _Error}),
	    ?shutdown(Node)
    end.


send_status(#hs_data{socket = Socket, other_node = Node,
		    f_send = FSend}, Stat) ->
    ?debug({dist_util,self(),send_status, Node, Stat}),
    case FSend(Socket, [$s | atom_to_list(Stat)]) of
	{error, _} ->
	    ?shutdown(Node);
	_ -> 
	    true
    end.
    
    

%%
%% Send a TICK to the other side.
%%
%% This will happen every 15 seconds (by default) 
%% The idea here is that every 15 secs, we write a little 
%% something on the connection if we haven't written anything for 
%% the last 15 secs.
%% This will ensure that nodes that are not responding due to 
%% hardware errors (Or being suspended by means of ^Z) will 
%% be considered to be down. If we do not want to have this  
%% we must start the net_kernel (in erlang) without its 
%% ticker process, In that case this code will never run 

%% And then every 60 seconds we also check the connection and 
%% close it if we havn't received anything on it for the 
%% last 60 secs. If ticked == tick we havn't received anything 
%% on the connection the last 60 secs. 

%% The detection time interval is thus, by default, 45s < DT < 75s 

%% A HIDDEN node is always (if not a pending write) ticked if 
%% we haven't read anything as a hidden node only ticks when it receives 
%% a TICK !! 
	
send_tick(Socket, Tick, Type, MFTick, MFGetstat) ->
    #tick{tick = T0,
	  read = Read,
	  write = Write,
	  ticked = Ticked} = Tick,
    T = T0 + 1,
    T1 = T rem 4,
    case MFGetstat(Socket) of
	{ok, Read, _, _} when  Ticked =:= T ->
	    {error, not_responding};
	{ok, Read, W, Pend} when Type =:= hidden ->
	    send_tick(Socket, Pend, MFTick),
	    {ok, Tick#tick{write = W + 1,
			   tick = T1}};
	{ok, Read, Write, Pend} ->
	    send_tick(Socket, Pend, MFTick),
	    {ok, Tick#tick{write = Write + 1,
			   tick = T1}};
	{ok, R, Write, Pend} ->
	    send_tick(Socket, Pend, MFTick),
	    {ok, Tick#tick{write = Write + 1,
			   read = R,
			   tick = T1,
			   ticked = T}};
	{ok, Read, W, _} ->
	    {ok, Tick#tick{write = W,
			   tick = T1}};
	{ok, R, W, _} ->
	    {ok, Tick#tick{write = W,
			   read = R,
			   tick = T1,
			   ticked = T}};
	Error ->
	    Error
    end.

send_tick(Socket, 0, MFTick) ->
    MFTick(Socket);
send_tick(_, _Pend, _) ->
    %% Dont send tick if pending write.
    ok.

%% ------------------------------------------------------------
%% Connection setup timeout timer.
%% After Timeout milliseconds this process terminates
%% which implies that the owning setup/accept process terminates.
%% The timer is reset before every network operation during the
%% connection setup !
%% ------------------------------------------------------------

start_timer(Timeout) ->
    spawn_link(?MODULE, setup_timer, [self(), Timeout*?trace_factor]).

setup_timer(Pid, Timeout) ->
    receive
	{Pid, reset} ->
	    setup_timer(Pid, Timeout)
    after Timeout ->
	    ?trace("Timer expires ~p, ~p~n",[Pid, Timeout]),
	    ?shutdown(timer)
    end.

reset_timer(Timer) ->
    Timer ! {self(), reset}.

cancel_timer(Timer) ->
    unlink(Timer),
    exit(Timer, shutdown).