aboutsummaryrefslogtreecommitdiff
path: root/tests/server/sockfilt.c
blob: 50e91f41df11ba8762af41c9ba23326e2a5a5b85 (plain)
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
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
977
978
979
980
981
982
983
984
985
986
987
988
989
990
991
992
993
994
995
996
997
998
999
1000
1001
1002
1003
1004
1005
1006
1007
1008
1009
1010
1011
1012
1013
1014
1015
1016
1017
1018
1019
1020
1021
1022
1023
1024
1025
1026
1027
1028
1029
1030
1031
1032
1033
1034
1035
1036
1037
1038
1039
1040
1041
1042
1043
1044
1045
1046
1047
1048
1049
1050
1051
1052
1053
1054
1055
/***************************************************************************
 *                                  _   _ ____  _
 *  Project                     ___| | | |  _ \| |
 *                             / __| | | | |_) | |
 *                            | (__| |_| |  _ <| |___
 *                             \___|\___/|_| \_\_____|
 *
 * Copyright (C) 1998 - 2010, Daniel Stenberg, <daniel@haxx.se>, et al.
 *
 * This software is licensed as described in the file COPYING, which
 * you should have received as part of this distribution. The terms
 * are also available at http://curl.haxx.se/docs/copyright.html.
 *
 * You may opt to use, copy, modify, merge, publish, distribute and/or sell
 * copies of the Software, and permit persons to whom the Software is
 * furnished to do so, under the terms of the COPYING file.
 *
 * This software is distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY
 * KIND, either express or implied.
 *
 * $Id$
 ***************************************************************************/

/* Purpose
 *
 * 1. Accept a TCP connection on a custom port (ipv4 or ipv6), or connect
 *    to a given (localhost) port.
 *
 * 2. Get commands on STDIN. Pass data on to the TCP stream.
 *    Get data from TCP stream and pass on to STDOUT.
 *
 * This program is made to perform all the socket/stream/connection stuff for
 * the test suite's (perl) FTP server. Previously the perl code did all of
 * this by its own, but I decided to let this program do the socket layer
 * because of several things:
 *
 * o We want the perl code to work with rather old perl installations, thus
 *   we cannot use recent perl modules or features.
 *
 * o We want IPv6 support for systems that provide it, and doing optional IPv6
 *   support in perl seems if not impossible so at least awkward.
 *
 * o We want FTP-SSL support, which means that a connection that starts with
 *   plain sockets needs to be able to "go SSL" in the midst. This would also
 *   require some nasty perl stuff I'd rather avoid.
 *
 * (Source originally based on sws.c)
 */

/*
 * Signal handling notes for sockfilt
 * ----------------------------------
 *
 * This program is a single-threaded process.
 *
 * This program is intended to be highly portable and as such it must be kept as
 * simple as possible, due to this the only signal handling mechanisms used will
 * be those of ANSI C, and used only in the most basic form which is good enough
 * for the purpose of this program.
 *
 * For the above reason and the specific needs of this program signals SIGHUP,
 * SIGPIPE and SIGALRM will be simply ignored on systems where this can be done.
 * If possible, signals SIGINT and SIGTERM will be handled by this program as an
 * indication to cleanup and finish execution as soon as possible.  This will be
 * achieved with a single signal handler 'exit_signal_handler' for both signals.
 *
 * The 'exit_signal_handler' upon the first SIGINT or SIGTERM received signal
 * will just set to one the global var 'got_exit_signal' storing in global var
 * 'exit_signal' the signal that triggered this change.
 *
 * Nothing fancy that could introduce problems is used, the program at certain
 * points in its normal flow checks if var 'got_exit_signal' is set and in case
 * this is true it just makes its way out of loops and functions in structured
 * and well behaved manner to achieve proper program cleanup and termination.
 *
 * Even with the above mechanism implemented it is worthwile to note that other
 * signals might still be received, or that there might be systems on which it
 * is not possible to trap and ignore some of the above signals.  This implies
 * that for increased portability and reliability the program must be coded as
 * if no signal was being ignored or handled at all.  Enjoy it!
 */

#define CURL_NO_OLDIES

#include "setup.h" /* portability help from the lib directory */

#ifdef HAVE_SIGNAL_H
#include <signal.h>
#endif
#ifdef HAVE_UNISTD_H
#include <unistd.h>
#endif
#ifdef HAVE_SYS_SOCKET_H
#include <sys/socket.h>
#endif
#ifdef HAVE_NETINET_IN_H
#include <netinet/in.h>
#endif
#ifdef HAVE_ARPA_INET_H
#include <arpa/inet.h>
#endif
#ifdef HAVE_NETDB_H
#include <netdb.h>
#endif

#define ENABLE_CURLX_PRINTF
/* make the curlx header define all printf() functions to use the curlx_*
   versions instead */
#include "curlx.h" /* from the private lib dir */
#include "getpart.h"
#include "inet_pton.h"
#include "util.h"
#include "warnless.h"

/* include memdebug.h last */
#include "memdebug.h"

#define DEFAULT_PORT 8999

#ifndef DEFAULT_LOGFILE
#define DEFAULT_LOGFILE "log/sockfilt.log"
#endif

const char *serverlogfile = DEFAULT_LOGFILE;

static bool verbose = FALSE;
#ifdef ENABLE_IPV6
static bool use_ipv6 = FALSE;
#endif
static const char *ipv_inuse = "IPv4";
static unsigned short port = DEFAULT_PORT;
static unsigned short connectport = 0; /* if non-zero, we activate this mode */

enum sockmode {
  PASSIVE_LISTEN,    /* as a server waiting for connections */
  PASSIVE_CONNECT,   /* as a server, connected to a client */
  ACTIVE,            /* as a client, connected to a server */
  ACTIVE_DISCONNECT  /* as a client, disconnected from server */
};

/* do-nothing macro replacement for systems which lack siginterrupt() */

#ifndef HAVE_SIGINTERRUPT
#define siginterrupt(x,y) do {} while(0)
#endif

/* vars used to keep around previous signal handlers */

typedef RETSIGTYPE (*SIGHANDLER_T)(int);

#ifdef SIGHUP
static SIGHANDLER_T old_sighup_handler  = SIG_ERR;
#endif

#ifdef SIGPIPE
static SIGHANDLER_T old_sigpipe_handler = SIG_ERR;
#endif

#ifdef SIGALRM
static SIGHANDLER_T old_sigalrm_handler = SIG_ERR;
#endif

#ifdef SIGINT
static SIGHANDLER_T old_sigint_handler  = SIG_ERR;
#endif

#ifdef SIGTERM
static SIGHANDLER_T old_sigterm_handler = SIG_ERR;
#endif

/* var which if set indicates that the program should finish execution */

SIG_ATOMIC_T got_exit_signal = 0;

/* if next is set indicates the first signal handled in exit_signal_handler */

static volatile int exit_signal = 0;

/* signal handler that will be triggered to indicate that the program
  should finish its execution in a controlled manner as soon as possible.
  The first time this is called it will set got_exit_signal to one and
  store in exit_signal the signal that triggered its execution. */

static RETSIGTYPE exit_signal_handler(int signum)
{
  int old_errno = ERRNO;
  if(got_exit_signal == 0) {
    got_exit_signal = 1;
    exit_signal = signum;
  }
  (void)signal(signum, exit_signal_handler);
  SET_ERRNO(old_errno);
}

static void install_signal_handlers(void)
{
#ifdef SIGHUP
  /* ignore SIGHUP signal */
  if((old_sighup_handler = signal(SIGHUP, SIG_IGN)) == SIG_ERR)
    logmsg("cannot install SIGHUP handler: %s", strerror(ERRNO));
#endif
#ifdef SIGPIPE
  /* ignore SIGPIPE signal */
  if((old_sigpipe_handler = signal(SIGPIPE, SIG_IGN)) == SIG_ERR)
    logmsg("cannot install SIGPIPE handler: %s", strerror(ERRNO));
#endif
#ifdef SIGALRM
  /* ignore SIGALRM signal */
  if((old_sigalrm_handler = signal(SIGALRM, SIG_IGN)) == SIG_ERR)
    logmsg("cannot install SIGALRM handler: %s", strerror(ERRNO));
#endif
#ifdef SIGINT
  /* handle SIGINT signal with our exit_signal_handler */
  if((old_sigint_handler = signal(SIGINT, exit_signal_handler)) == SIG_ERR)
    logmsg("cannot install SIGINT handler: %s", strerror(ERRNO));
  else
    siginterrupt(SIGINT, 1);
#endif
#ifdef SIGTERM
  /* handle SIGTERM signal with our exit_signal_handler */
  if((old_sigterm_handler = signal(SIGTERM, exit_signal_handler)) == SIG_ERR)
    logmsg("cannot install SIGTERM handler: %s", strerror(ERRNO));
  else
    siginterrupt(SIGTERM, 1);
#endif
}

static void restore_signal_handlers(void)
{
#ifdef SIGHUP
  if(SIG_ERR != old_sighup_handler)
    (void)signal(SIGHUP, old_sighup_handler);
#endif
#ifdef SIGPIPE
  if(SIG_ERR != old_sigpipe_handler)
    (void)signal(SIGPIPE, old_sigpipe_handler);
#endif
#ifdef SIGALRM
  if(SIG_ERR != old_sigalrm_handler)
    (void)signal(SIGALRM, old_sigalrm_handler);
#endif
#ifdef SIGINT
  if(SIG_ERR != old_sigint_handler)
    (void)signal(SIGINT, old_sigint_handler);
#endif
#ifdef SIGTERM
  if(SIG_ERR != old_sigterm_handler)
    (void)signal(SIGTERM, old_sigterm_handler);
#endif
}

/*
 * fullread is a wrapper around the read() function. This will repeat the call
 * to read() until it actually has read the complete number of bytes indicated
 * in nbytes or it fails with a condition that cannot be handled with a simple
 * retry of the read call.
 */

static ssize_t fullread(int filedes, void *buffer, size_t nbytes)
{
  int error;
  ssize_t rc;
  ssize_t nread = 0;

  do {
    rc = read(filedes, (unsigned char *)buffer + nread, nbytes - nread);

    if(got_exit_signal) {
      logmsg("signalled to die");
      return -1;
    }

    if(rc < 0) {
      error = ERRNO;
      if((error == EINTR) || (error == EAGAIN))
        continue;
      logmsg("unrecoverable read() failure: %s", strerror(error));
      return -1;
    }

    if(rc == 0) {
      logmsg("got 0 reading from stdin");
      return 0;
    }

    nread += rc;

  } while((size_t)nread < nbytes);

  if(verbose)
    logmsg("read %zd bytes", nread);

  return nread;
}

/*
 * fullwrite is a wrapper around the write() function. This will repeat the
 * call to write() until it actually has written the complete number of bytes
 * indicated in nbytes or it fails with a condition that cannot be handled
 * with a simple retry of the write call.
 */

static ssize_t fullwrite(int filedes, const void *buffer, size_t nbytes)
{
  int error;
  ssize_t wc;
  ssize_t nwrite = 0;

  do {
    wc = write(filedes, (unsigned char *)buffer + nwrite, nbytes - nwrite);

    if(got_exit_signal) {
      logmsg("signalled to die");
      return -1;
    }

    if(wc < 0) {
      error = ERRNO;
      if((error == EINTR) || (error == EAGAIN))
        continue;
      logmsg("unrecoverable write() failure: %s", strerror(error));
      return -1;
    }

    if(wc == 0) {
      logmsg("put 0 writing to stdout");
      return 0;
    }

    nwrite += wc;

  } while((size_t)nwrite < nbytes);

  if(verbose)
    logmsg("wrote %zd bytes", nwrite);

  return nwrite;
}

/*
 * read_stdin tries to read from stdin nbytes into the given buffer. This is a
 * blocking function that will only return TRUE when nbytes have actually been
 * read or FALSE when an unrecoverable error has been detected. Failure of this
 * function is an indication that the sockfilt process should terminate.
 */

static bool read_stdin(void *buffer, size_t nbytes)
{
  ssize_t nread = fullread(fileno(stdin), buffer, nbytes);
  if(nread != (ssize_t)nbytes) {
    logmsg("exiting...");
    return FALSE;
  }
  return TRUE;
}

/*
 * write_stdout tries to write to stdio nbytes from the given buffer. This is a
 * blocking function that will only return TRUE when nbytes have actually been
 * written or FALSE when an unrecoverable error has been detected. Failure of
 * this function is an indication that the sockfilt process should terminate.
 */

static bool write_stdout(const void *buffer, size_t nbytes)
{
  ssize_t nwrite = fullwrite(fileno(stdout), buffer, nbytes);
  if(nwrite != (ssize_t)nbytes) {
    logmsg("exiting...");
    return FALSE;
  }
  return TRUE;
}

static void lograw(unsigned char *buffer, ssize_t len)
{
  char data[120];
  ssize_t i;
  unsigned char *ptr = buffer;
  char *optr = data;
  ssize_t width=0;

  for(i=0; i<len; i++) {
    switch(ptr[i]) {
    case '\n':
      sprintf(optr, "\\n");
      width += 2;
      optr += 2;
      break;
    case '\r':
      sprintf(optr, "\\r");
      width += 2;
      optr += 2;
      break;
    default:
      sprintf(optr, "%c", (ISGRAPH(ptr[i]) || ptr[i]==0x20) ?ptr[i]:'.');
      width++;
      optr++;
      break;
    }

    if(width>60) {
      logmsg("'%s'", data);
      width = 0;
      optr = data;
    }
  }
  if(width)
    logmsg("'%s'", data);
}

/*
  sockfdp is a pointer to an established stream or CURL_SOCKET_BAD

  if sockfd is CURL_SOCKET_BAD, listendfd is a listening socket we must
  accept()
*/
static bool juggle(curl_socket_t *sockfdp,
                   curl_socket_t listenfd,
                   enum sockmode *mode)
{
  struct timeval timeout;
  fd_set fds_read;
  fd_set fds_write;
  fd_set fds_err;
  curl_socket_t sockfd = CURL_SOCKET_BAD;
  curl_socket_t maxfd = CURL_SOCKET_BAD;
  ssize_t rc;
  ssize_t nread_socket;
  ssize_t bytes_written;
  ssize_t buffer_len;
  int error = 0;

 /* 'buffer' is this excessively large only to be able to support things like
    test 1003 which tests exceedingly large server response lines */
  unsigned char buffer[17010];
  char data[16];

  if(got_exit_signal) {
    logmsg("signalled to die, exiting...");
    return FALSE;
  }

#ifdef HAVE_GETPPID
  /* As a last resort, quit if sockfilt process becomes orphan. Just in case
     parent ftpserver process has died without killing its sockfilt children */
  if(getppid() <= 1) {
    logmsg("process becomes orphan, exiting");
    return FALSE;
  }
#endif

  timeout.tv_sec = 120;
  timeout.tv_usec = 0;

  FD_ZERO(&fds_read);
  FD_ZERO(&fds_write);
  FD_ZERO(&fds_err);

#ifdef USE_WINSOCK
  /*
  ** WinSock select() does not support standard file descriptors,
  ** it can only check SOCKETs. Since this program in its current
  ** state will not work on WinSock based systems, next line is
  ** commented out to allow warning-free compilation awaiting the
  ** day it will be fixed to also run on WinSock systems.
  */
#else
  FD_SET(fileno(stdin), &fds_read);
#endif

  switch(*mode) {

  case PASSIVE_LISTEN:

    /* server mode */
    sockfd = listenfd;
    /* there's always a socket to wait for */
    FD_SET(sockfd, &fds_read);
    maxfd = sockfd;
    break;

  case PASSIVE_CONNECT:

    sockfd = *sockfdp;
    if(CURL_SOCKET_BAD == sockfd) {
      /* eeek, we are supposedly connected and then this cannot be -1 ! */
      logmsg("socket is -1! on %s:%d", __FILE__, __LINE__);
      maxfd = 0; /* stdin */
    }
    else {
      /* there's always a socket to wait for */
      FD_SET(sockfd, &fds_read);
      maxfd = sockfd;
    }
    break;

  case ACTIVE:

    sockfd = *sockfdp;
    /* sockfd turns CURL_SOCKET_BAD when our connection has been closed */
    if(CURL_SOCKET_BAD != sockfd) {
      FD_SET(sockfd, &fds_read);
      maxfd = sockfd;
    }
    else {
      logmsg("No socket to read on");
      maxfd = 0;
    }
    break;

  case ACTIVE_DISCONNECT:

    logmsg("disconnected, no socket to read on");
    maxfd = 0;
    sockfd = CURL_SOCKET_BAD;
    break;

  } /* switch(*mode) */


  do {

    rc = select((int)maxfd + 1, &fds_read, &fds_write, &fds_err, &timeout);

    if(got_exit_signal) {
      logmsg("signalled to die, exiting...");
      return FALSE;
    }

  } while((rc == -1) && ((error = SOCKERRNO) == EINTR));

  if(rc < 0) {
    logmsg("select() failed with error: (%d) %s",
           error, strerror(error));
    return FALSE;
  }

  if(rc == 0)
    /* timeout */
    return TRUE;


  if(FD_ISSET(fileno(stdin), &fds_read)) {
    /* read from stdin, commands/data to be dealt with and possibly passed on
       to the socket

       protocol:

       4 letter command + LF [mandatory]

       4-digit hexadecimal data length + LF [if the command takes data]
       data                       [the data being as long as set above]

       Commands:

       DATA - plain pass-thru data
    */

    if(!read_stdin(buffer, 5))
      return FALSE;

    logmsg("Received %c%c%c%c (on stdin)",
           buffer[0], buffer[1], buffer[2], buffer[3] );

    if(!memcmp("PING", buffer, 4)) {
      /* send reply on stdout, just proving we are alive */
      if(!write_stdout("PONG\n", 5))
        return FALSE;
    }

    else if(!memcmp("PORT", buffer, 4)) {
      /* Question asking us what PORT number we are listening to.
         Replies to PORT with "IPv[num]/[port]" */
      sprintf((char *)buffer, "%s/%hu\n", ipv_inuse, port);
      buffer_len = (ssize_t)strlen((char *)buffer);
      snprintf(data, sizeof(data), "PORT\n%04zx\n", buffer_len);
      if(!write_stdout(data, 10))
        return FALSE;
      if(!write_stdout(buffer, buffer_len))
        return FALSE;
    }
    else if(!memcmp("QUIT", buffer, 4)) {
      /* just die */
      logmsg("quits");
      return FALSE;
    }
    else if(!memcmp("DATA", buffer, 4)) {
      /* data IN => data OUT */

      if(!read_stdin(buffer, 5))
        return FALSE;

      buffer[5] = '\0';

      buffer_len = (ssize_t)strtol((char *)buffer, NULL, 16);
      if (buffer_len > (ssize_t)sizeof(buffer)) {
        logmsg("ERROR: Buffer size (%zu bytes) too small for data size "
               "(%zd bytes)", sizeof(buffer), buffer_len);
        return FALSE;
      }
      logmsg("> %zd bytes data, server => client", buffer_len);

      if(!read_stdin(buffer, buffer_len))
        return FALSE;

      lograw(buffer, buffer_len);

      if(*mode == PASSIVE_LISTEN) {
        logmsg("*** We are disconnected!");
        if(!write_stdout("DISC\n", 5))
          return FALSE;
      }
      else {
        /* send away on the socket */
        bytes_written = swrite(sockfd, buffer, buffer_len);
        if(bytes_written != buffer_len) {
          logmsg("Not all data was sent. Bytes to send: %zd sent: %zd",
                 buffer_len, bytes_written);
        }
      }
    }
    else if(!memcmp("DISC", buffer, 4)) {
      /* disconnect! */
      if(!write_stdout("DISC\n", 5))
        return FALSE;
      if(sockfd != CURL_SOCKET_BAD) {
        logmsg("====> Client forcibly disconnected");
        sclose(sockfd);
        *sockfdp = CURL_SOCKET_BAD;
        if(*mode == PASSIVE_CONNECT)
          *mode = PASSIVE_LISTEN;
        else
          *mode = ACTIVE_DISCONNECT;
      }
      else
        logmsg("attempt to close already dead connection");
      return TRUE;
    }
  }


  if((sockfd != CURL_SOCKET_BAD) && (FD_ISSET(sockfd, &fds_read)) ) {

    if(*mode == PASSIVE_LISTEN) {
      /* there's no stream set up yet, this is an indication that there's a
         client connecting. */
      sockfd = accept(sockfd, NULL, NULL);
      if(CURL_SOCKET_BAD == sockfd)
        logmsg("accept() failed");
      else {
        logmsg("====> Client connect");
        if(!write_stdout("CNCT\n", 5))
          return FALSE;
        *sockfdp = sockfd; /* store the new socket */
        *mode = PASSIVE_CONNECT; /* we have connected */
      }
      return TRUE;
    }

    /* read from socket, pass on data to stdout */
    nread_socket = sread(sockfd, buffer, sizeof(buffer));

    if(nread_socket <= 0) {
      logmsg("====> Client disconnect");
      if(!write_stdout("DISC\n", 5))
        return FALSE;
      sclose(sockfd);
      *sockfdp = CURL_SOCKET_BAD;
      if(*mode == PASSIVE_CONNECT)
        *mode = PASSIVE_LISTEN;
      else
        *mode = ACTIVE_DISCONNECT;
      return TRUE;
    }

    snprintf(data, sizeof(data), "DATA\n%04zx\n", nread_socket);
    if(!write_stdout(data, 10))
      return FALSE;
    if(!write_stdout(buffer, nread_socket))
      return FALSE;

    logmsg("< %zd bytes data, client => server", nread_socket);
    lograw(buffer, nread_socket);
  }

  return TRUE;
}

static curl_socket_t sockdaemon(curl_socket_t sock,
                                unsigned short *listenport)
{
  /* passive daemon style */
  struct sockaddr_in me;
#ifdef ENABLE_IPV6
  struct sockaddr_in6 me6;
#endif /* ENABLE_IPV6 */
  int flag;
  int rc;
  int totdelay = 0;
  int maxretr = 10;
  int delay= 20;
  int attempt = 0;
  int error = 0;

  do {
    attempt++;
    flag = 1;
    rc = setsockopt(sock, SOL_SOCKET, SO_REUSEADDR,
         (void *)&flag, sizeof(flag));
    if(rc) {
      error = SOCKERRNO;
      logmsg("setsockopt(SO_REUSEADDR) failed with error: (%d) %s",
             error, strerror(error));
      if(maxretr) {
        rc = wait_ms(delay);
        if(rc) {
          /* should not happen */
          error = SOCKERRNO;
          logmsg("wait_ms() failed with error: (%d) %s",
                 error, strerror(error));
          sclose(sock);
          return CURL_SOCKET_BAD;
        }
        if(got_exit_signal) {
          logmsg("signalled to die, exiting...");
          sclose(sock);
          return CURL_SOCKET_BAD;
        }
        totdelay += delay;
        delay *= 2; /* double the sleep for next attempt */
      }
    }
  } while(rc && maxretr--);

  if(rc) {
    logmsg("setsockopt(SO_REUSEADDR) failed %d times in %d ms. Error: (%d) %s",
           attempt, totdelay, error, strerror(error));
    logmsg("Continuing anyway...");
  }

  /* When the specified listener port is zero, it is actually a
     request to let the system choose a non-zero available port. */

#ifdef ENABLE_IPV6
  if(!use_ipv6) {
#endif
    memset(&me, 0, sizeof(me));
    me.sin_family = AF_INET;
    me.sin_addr.s_addr = INADDR_ANY;
    me.sin_port = htons(*listenport);
    rc = bind(sock, (struct sockaddr *) &me, sizeof(me));
#ifdef ENABLE_IPV6
  }
  else {
    memset(&me6, 0, sizeof(me6));
    me6.sin6_family = AF_INET6;
    me6.sin6_addr = in6addr_any;
    me6.sin6_port = htons(*listenport);
    rc = bind(sock, (struct sockaddr *) &me6, sizeof(me6));
  }
#endif /* ENABLE_IPV6 */
  if(rc) {
    error = SOCKERRNO;
    logmsg("Error binding socket on port %hu: (%d) %s",
           *listenport, error, strerror(error));
    sclose(sock);
    return CURL_SOCKET_BAD;
  }

  if(!*listenport) {
    /* The system was supposed to choose a port number, figure out which
       port we actually got and update the listener port value with it. */
    curl_socklen_t la_size;
    struct sockaddr *localaddr;
    struct sockaddr_in localaddr4;
#ifdef ENABLE_IPV6
    struct sockaddr_in6 localaddr6;
    if(!use_ipv6) {
#endif
      la_size = sizeof(localaddr4);
      localaddr = (struct sockaddr *)&localaddr4;
#ifdef ENABLE_IPV6
    }
    else {
      la_size = sizeof(localaddr6);
      localaddr = (struct sockaddr *)&localaddr6;
    }
#endif
    memset(localaddr, 0, (size_t)la_size);
    if(getsockname(sock, localaddr, &la_size) < 0) {
      error = SOCKERRNO;
      logmsg("getsockname() failed with error: (%d) %s",
             error, strerror(error));
      sclose(sock);
      return CURL_SOCKET_BAD;
    }
    switch (localaddr->sa_family) {
    case AF_INET:
      *listenport = ntohs(localaddr4.sin_port);
      break;
#ifdef ENABLE_IPV6
    case AF_INET6:
      *listenport = ntohs(localaddr6.sin6_port);
      break;
#endif
    default:
      break;
    }
    if(!*listenport) {
      /* Real failure, listener port shall not be zero beyond this point. */
      logmsg("Apparently getsockname() succeeded, with listener port zero.");
      logmsg("A valid reason for this failure is a binary built without");
      logmsg("proper network library linkage. This might not be the only");
      logmsg("reason, but double check it before anything else.");
      sclose(sock);
      return CURL_SOCKET_BAD;
    }
  }

  /* start accepting connections */
  rc = listen(sock, 5);
  if(0 != rc) {
    error = SOCKERRNO;
    logmsg("listen() failed with error: (%d) %s",
           error, strerror(error));
    sclose(sock);
    return CURL_SOCKET_BAD;
  }

  return sock;
}


int main(int argc, char *argv[])
{
  struct sockaddr_in me;
#ifdef ENABLE_IPV6
  struct sockaddr_in6 me6;
#endif /* ENABLE_IPV6 */
  curl_socket_t sock = CURL_SOCKET_BAD;
  curl_socket_t msgsock = CURL_SOCKET_BAD;
  int wrotepidfile = 0;
  char *pidname= (char *)".sockfilt.pid";
  bool juggle_again;
  int rc;
  int error;
  int arg=1;
  enum sockmode mode = PASSIVE_LISTEN; /* default */
  const char *addr = NULL;

  while(argc>arg) {
    if(!strcmp("--version", argv[arg])) {
      printf("sockfilt IPv4%s\n",
#ifdef ENABLE_IPV6
             "/IPv6"
#else
             ""
#endif
             );
      return 0;
    }
    else if(!strcmp("--verbose", argv[arg])) {
      verbose = TRUE;
      arg++;
    }
    else if(!strcmp("--pidfile", argv[arg])) {
      arg++;
      if(argc>arg)
        pidname = argv[arg++];
    }
    else if(!strcmp("--logfile", argv[arg])) {
      arg++;
      if(argc>arg)
        serverlogfile = argv[arg++];
    }
    else if(!strcmp("--ipv6", argv[arg])) {
#ifdef ENABLE_IPV6
      ipv_inuse = "IPv6";
      use_ipv6 = TRUE;
#endif
      arg++;
    }
    else if(!strcmp("--ipv4", argv[arg])) {
      /* for completeness, we support this option as well */
#ifdef ENABLE_IPV6
      ipv_inuse = "IPv4";
      use_ipv6 = FALSE;
#endif
      arg++;
    }
    else if(!strcmp("--port", argv[arg])) {
      arg++;
      if(argc>arg) {
        char *endptr;
        unsigned long ulnum = strtoul(argv[arg], &endptr, 10);
        if((endptr != argv[arg] + strlen(argv[arg])) ||
           ((ulnum != 0UL) && ((ulnum < 1025UL) || (ulnum > 65535UL)))) {
          fprintf(stderr, "sockfilt: invalid --port argument (%s)\n",
                  argv[arg]);
          return 0;
        }
        port = Curl_ultous(ulnum);
        arg++;
      }
    }
    else if(!strcmp("--connect", argv[arg])) {
      /* Asked to actively connect to the specified local port instead of
         doing a passive server-style listening. */
      arg++;
      if(argc>arg) {
        char *endptr;
        unsigned long ulnum = strtoul(argv[arg], &endptr, 10);
        if((endptr != argv[arg] + strlen(argv[arg])) ||
           (ulnum < 1025UL) || (ulnum > 65535UL)) {
          fprintf(stderr, "sockfilt: invalid --connect argument (%s)\n",
                  argv[arg]);
          return 0;
        }
        connectport = Curl_ultous(ulnum);
        arg++;
      }
    }
    else if(!strcmp("--addr", argv[arg])) {
      /* Set an IP address to use with --connect; otherwise use localhost */
      arg++;
      if(argc>arg) {
        addr = argv[arg];
        arg++;
      }
    }
    else {
      puts("Usage: sockfilt [option]\n"
           " --version\n"
           " --verbose\n"
           " --logfile [file]\n"
           " --pidfile [file]\n"
           " --ipv4\n"
           " --ipv6\n"
           " --port [port]\n"
           " --connect [port]\n"
           " --addr [address]");
      return 0;
    }
  }

#ifdef WIN32
  win32_init();
  atexit(win32_cleanup);
#endif

  install_signal_handlers();

#ifdef ENABLE_IPV6
  if(!use_ipv6)
#endif
    sock = socket(AF_INET, SOCK_STREAM, 0);
#ifdef ENABLE_IPV6
  else
    sock = socket(AF_INET6, SOCK_STREAM, 0);
#endif

  if(CURL_SOCKET_BAD == sock) {
    error = SOCKERRNO;
    logmsg("Error creating socket: (%d) %s",
           error, strerror(error));
    goto sockfilt_cleanup;
  }

  if(connectport) {
    /* Active mode, we should connect to the given port number */
    mode = ACTIVE;
#ifdef ENABLE_IPV6
    if(!use_ipv6) {
#endif
      memset(&me, 0, sizeof(me));
      me.sin_family = AF_INET;
      me.sin_port = htons(connectport);
      me.sin_addr.s_addr = INADDR_ANY;
      if (!addr)
        addr = "127.0.0.1";
      Curl_inet_pton(AF_INET, addr, &me.sin_addr);

      rc = connect(sock, (struct sockaddr *) &me, sizeof(me));
#ifdef ENABLE_IPV6
    }
    else {
      memset(&me6, 0, sizeof(me6));
      me6.sin6_family = AF_INET6;
      me6.sin6_port = htons(connectport);
      if (!addr)
        addr = "::1";
      Curl_inet_pton(AF_INET6, addr, &me6.sin6_addr);

      rc = connect(sock, (struct sockaddr *) &me6, sizeof(me6));
    }
#endif /* ENABLE_IPV6 */
    if(rc) {
      error = SOCKERRNO;
      logmsg("Error connecting to port %hu: (%d) %s",
             connectport, error, strerror(error));
      goto sockfilt_cleanup;
    }
    logmsg("====> Client connect");
    msgsock = sock; /* use this as stream */
  }
  else {
    /* passive daemon style */
    sock = sockdaemon(sock, &port);
    if(CURL_SOCKET_BAD == sock)
      goto sockfilt_cleanup;
    msgsock = CURL_SOCKET_BAD; /* no stream socket yet */
  }

  logmsg("Running %s version", ipv_inuse);

  if(connectport)
    logmsg("Connected to port %hu", connectport);
  else
    logmsg("Listening on port %hu", port);

  wrotepidfile = write_pidfile(pidname);
  if(!wrotepidfile)
    goto sockfilt_cleanup;

  do {
    juggle_again = juggle(&msgsock, sock, &mode);
  } while(juggle_again);

sockfilt_cleanup:

  if((msgsock != sock) && (msgsock != CURL_SOCKET_BAD))
    sclose(msgsock);

  if(sock != CURL_SOCKET_BAD)
    sclose(sock);

  if(wrotepidfile)
    unlink(pidname);

  restore_signal_handlers();

  if(got_exit_signal) {
    logmsg("============> sockfilt exits with signal (%d)", exit_signal);
    /*
     * To properly set the return status of the process we
     * must raise the same signal SIGINT or SIGTERM that we
     * caught and let the old handler take care of it.
     */
    raise(exit_signal);
  }

  logmsg("============> sockfilt quits");
  return 0;
}