aboutsummaryrefslogtreecommitdiff
path: root/bbot/agent.cxx
blob: 2df96e63036498a30dc9c4c637d626b9b4bb1671 (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
// file      : bbot/agent.cxx -*- C++ -*-
// copyright : Copyright (c) 2014-2017 Code Synthesis Ltd
// license   : TBC; see accompanying LICENSE file

#include <bbot/agent>

#include <pwd.h>    // getpwuid()
#include <limits.h> // PATH_MAX
#include <signal.h> // signal()
#include <unistd.h> // sleep(), realink(), getuid()

#include <net/if.h>     // ifreq
#include <netinet/in.h> // sockaddr_in
#include <arpa/inet.h>  // inet_ntop()
#include <sys/ioctl.h>
#include <sys/socket.h>

#include <iostream>

#include <butl/pager>
#include <butl/filesystem> // dir_iterator

#include <bbot/manifest>

#include <bbot/types>
#include <bbot/utility>
#include <bbot/diagnostics>

#include <bbot/tftp>
#include <bbot/machine>
#include <bbot/machine-manifest>
#include <bbot/bootstrap-manifest>

using namespace std;
using namespace butl;
using namespace bbot;

namespace bbot
{
  agent_options ops;

  const string bs_prot ("1");

  string tc_name;
  size_t tc_num;
  string tc_id;

  string hname;
  uid_t  uid;
  string uname;

  // Note: Linux-specific implementation.
  //
  string
  iface_addr (const string& i)
  {
    if (i.size () >= IFNAMSIZ)
      throw invalid_argument ("interface nama too long");

    auto_fd fd (socket (AF_INET, SOCK_DGRAM | SOCK_CLOEXEC, 0));

    if (fd.get () == -1)
      throw_system_error (errno);

    ifreq ifr;
    ifr.ifr_addr.sa_family = AF_INET;
    strcpy (ifr.ifr_name, i.c_str ());

    if (ioctl (fd.get (), SIOCGIFADDR, &ifr) == -1)
      throw_system_error (errno);

    char buf[3 * 4 + 3 + 1]; // IPv4 address.
    if (inet_ntop (AF_INET,
                   &reinterpret_cast<sockaddr_in*> (&ifr.ifr_addr)->sin_addr,
                   buf,
                   sizeof (buf)) == nullptr)
      throw_system_error (errno);

    return buf;
  }
}

// The btrfs tool likes to print informational messages, like "Created
// snapshot such and such". Luckily, it writes them to stdout while proper
// diagnostics to stderr.
//
template <typename... A>
inline void
run_btrfs (tracer& t, A&&... a)
{
  if (verb >= 4)
    run_io (t, fdnull (), 2, 2, "btrfs", forward<A> (a)...);
  else
    run_io (t, fdnull (), fdnull (), 2, "btrfs", forward<A> (a)...);
}

template <typename... A>
inline butl::process_exit::code_type
btrfs_exit (tracer& t, A&&... a)
{
  return verb >= 4
    ? run_io_exit (t, fdnull (), 2, 2, "btrfs", forward<A> (a)...)
    : run_io_exit (t, fdnull (), fdnull (), 2, "btrfs", forward<A> (a)...);
}

// Bootstrap the machine. Return the bootstrapped machine manifest if
// successful and nullopt otherwise (in which case the machine directory
// should be cleaned and the machine ignored for now).
//
static optional<bootstrapped_machine_manifest>
bootstrap_machine (const dir_path& md,
                   const machine_manifest& mm,
                   optional<bootstrapped_machine_manifest> obmm)
{
  tracer trace ("bootstrap_machine");

  bootstrapped_machine_manifest r {
    mm,
    toolchain_manifest {tc_id.empty () ? "bogus" : tc_id},
    bootstrap_manifest {
      bootstrap_manifest::versions_type {
        {"bbot",    BBOT_VERSION},
        {"libbbot", LIBBBOT_VERSION},
        {"libbpkg", LIBBPKG_VERSION},
        {"libbutl", LIBBUTL_VERSION}
      }
    }
  };

  if (ops.fake_bootstrap ())
  {
    r.machine.mac = "de:ad:be:ef:de:ad";
  }
  else
  try
  {
    string br ("br1"); // Using private bridge for now.

    // Start the TFTP server (server chroot is --tftp). Map:
    //
    // GET requests to .../toolchain/<name>/*
    // PUT requests to .../bootstrap/<name>/*
    //
    auto_rmdir arm ((dir_path (ops.tftp ()) /= "bootstrap") /= tc_name);
    try_mkdir_p (arm.path ());

    // Bootstrap result manifest.
    //
    path mf (arm.path () / "manifest");
    try_rmfile (mf);

    tftp_server tftpd ("Gr  ^/?(.+)$  /toolchain/" + tc_name + "/\\1\n" +
                       "Pr  ^/?(.+)$  /bootstrap/" + tc_name + "/\\1\n");

    l3 ([&]{trace << "tftp server on port " << tftpd.port ();});

    // Start the machine.
    //
    unique_ptr<machine> m (
      start_machine (md,
                     mm,
                     obmm ? obmm->machine.mac : nullopt,
                     br,
                     tftpd.port ()));

    {
      // If we are terminating with an exception then force the machine down.
      // Failed that, the machine's destructor will block waiting for its
      // completion.
      //
      auto mg (
        make_exception_guard (
          [&m, &md] ()
          {
            info << "trying to force machine " << md << " down";
            try {m->forcedown ();} catch (const failed&) {}
          }));

      // What happens if the bootstrap process hangs? The simple thing would
      // be to force the machine down after some timeout and then fail. But
      // that won't be very helpful for investigating the cause. So instead
      // the plan is to suspend it after some timeout, issue diagnostics
      // (without failing and which Build OS monitor will relay to the admin),
      // and wait for the external intervention.
      //
      auto soft_fail = [&md, &m] (const char* msg)
      {
        {
          diag_record dr (error);
          dr << msg << " for machine " << md << ", suspending";
          m->print_info (dr);
        }
        m->suspend ();
        m->wait ();
        return nullopt;
      };

      // The first request should be the toolchain download. Wait for up to 60
      // seconds for that to arrive. In a sense we use it as an indication
      // that the machine has booted and the bootstrap process has started.
      //
      size_t to;
      const size_t startup_to   (60);
      const size_t bootstrap_to (ops.bootstrap_timeout ());
      const size_t shutdown_to  (60);

      if (!tftpd.serve ((to = startup_to)))
        return soft_fail ("bootstrap startup timeout");

      l3 ([&]{trace << "completed startup in " << startup_to - to << "s";});

      // Next the bootstrap process may download additional toolchain
      // archives, build things, and then upload the result manifest. So on
      // our side we serve TFTP requests while periodically checking for the
      // manifest file.
      //
      for (to = bootstrap_to; to != 0 && !file_exists (mf); tftpd.serve (to)) ;

      if (to == 0)
        return soft_fail ("bootstrap timeout");

      l3 ([&]{trace << "completed bootstrap in " << bootstrap_to - to << "s";});

      // Shut the machine down cleanly.
      //
      if (!m->shutdown ((to = shutdown_to)))
        return soft_fail ("bootstrap shutdown timeout");

      l3 ([&]{trace << "completed shutdown in " << shutdown_to - to << "s";});
    }

    // Parse the result manifest.
    //
    r.bootstrap = parse_manifest<bootstrap_manifest> (mf, "bootstrap");

    r.machine.mac = m->mac; // Save the MAC address.
  }
  catch (const system_error& e)
  {
    fail << "bootstrap error: " << e;
  }

  serialize_manifest (r, md / "manifest", "bootstrapped machine");
  return r;
}

// Return available machines and their directories as a parallel array.
//
static pair<bootstrapped_machine_manifests, dir_paths>
enumerate_machines (const dir_path& machines)
try
{
  tracer trace ("enumerate_machines");

  bootstrapped_machine_manifests rm;
  dir_paths rd;

  if (ops.fake_machine_specified ())
  {
    auto mh (
      parse_manifest<machine_header_manifest> (
        ops.fake_machine (), "machine header"));

    rm.push_back (
      bootstrapped_machine_manifest {
        machine_manifest {mh.id, mh.name, mh.summary, machine_type::kvm},
        toolchain_manifest {tc_id},
        bootstrap_manifest {}
      });

    rd.push_back (dir_path (ops.machines ()) /= mh.name); // For diagnostics.

    return make_pair (move (rm), move (rd));
  }

  // The first level are machine volumes.
  //
  for (const dir_entry& ve: dir_iterator (machines))
  {
    const string vn (ve.path ().string ());

    // Ignore hidden directories.
    //
    if (ve.type () != entry_type::directory || vn[0] == '.')
      continue;

    const dir_path vd (dir_path (machines) /= vn);

    // Inside we have machines.
    //
    try
    {
      for (const dir_entry& me: dir_iterator (vd))
      {
        const string mn (me.path ().string ());

        if (me.type () != entry_type::directory || mn[0] == '.')
          continue;

        const dir_path md (dir_path (vd) /= mn);

        // Our endgoal here is to obtain a bootstrapped snapshot of this
        // machine while watching out for potential race conditions (machines
        // being added/upgraded/removed; see the manual for details).
        //
        // So here is our overall plan:
        //
        // 1. Resolve current subvolume link for our bootstrap protocol.
        //
        // 2. If there is no link, cleanup and ignore this machine.
        //
        // 3. Try to create a snapshot of current subvolume (this operation is
        //    atomic). If failed (e.g., someone changed the link and removed
        //    the subvolume in the meantime), retry from #1.
        //
        // 4. Compare the snapshot to the already bootstrapped version (if
        //    any) and see if we need to re-bootstrap. If so, use the snapshot
        //    as a starting point. Rename to bootstrapped at the end (atomic).
        //
        dir_path lp (dir_path (md) /= (mn + '-' + bs_prot)); // -<P>
        dir_path tp (dir_path (md) /= (mn + '-' + tc_name)); // -<toolchain>
        bool te (dir_exists (tp));

        auto delete_t = [&tp, &trace] ()
        {
          run_btrfs (trace, "property", "set", "-ts", tp, "ro", "false");
          run_btrfs (trace, "subvolume", "delete", tp);
        };

        for (size_t retry (0);; ++retry)
        {
          if (retry != 0)
            sleep (1);

          // Resolve the link to subvolume path.
          //
          dir_path sp; // <name>-<P>.<R>
          try
          {
            char b [PATH_MAX + 1];
            ssize_t r (readlink (lp.string ().c_str (), b, sizeof (b)));

            if (r == -1)
            {
              if (errno != ENOENT)
                throw_generic_error (errno);
            }
            else if (static_cast<size_t> (r) >= sizeof (b))
              throw_generic_error (EINVAL);
            else
            {
              b[r] = '\0';
              sp = dir_path (b);
              if (sp.relative ())
                sp = md / sp;
            }
          }
          catch (const system_error& e)
          {
            fail << "unable to read subvolume link " << lp << ": " << e;
          }

          // If the resolution fails, then this means there is no current
          // machine subvolume (for this bootstrap protocol). In this case we
          // clean up our toolchain subvolume (<name>-<toolchain>) and ignore
          // this machine.
          //
          if (sp.empty ())
          {
            if (te)
              delete_t ();

            l3 ([&]{trace << "skipping " << md << ": no subvolume link";});
            break;
          }

          // <name>-<toolchain>-<xxx>
          //
          const dir_path xp (
            dir_path (md) /= path::traits::temp_name (mn + '-' + tc_name));

          if (btrfs_exit (trace, "subvolume", "snapshot", sp, xp) != 0)
          {
            if (retry >= 10)
              fail << "unable to snapshot subvolume " << sp;

            continue;
          }

          // Load the (original) machine manifest.
          //
          auto mm (
            parse_manifest<machine_manifest> (sp / "manifest", "machine"));

          // If we already have <name>-<toolchain>, see if it needs to be re-
          // bootstrapped. Things that render it obsolete:
          //
          // 1. New machine revision  (compare machine ids).
          // 2. New toolchain         (compare toolchain ids).
          // 3. New bbot/libbbot      (compare versions).
          //
          // The last case has a complication: what should we do if we have
          // bootstrapped a newer version of bbot? This would mean that we are
          // about to be stopped and upgraded (and the upgraded version will
          // probably be able to use the result). So we simply ignore this
          // machine for this run.

          // Return -1 if older, 0 if the same, and +1 if newer.
          //
          auto compare_bbot = [] (const bootstrap_manifest& m) -> int
          {
            auto cmp = [&m] (const string& n, uint64_t v) -> int
            {
              auto i = m.versions.find (n);
              return
                i == m.versions.end () || i->second < v
                ? -1
                : i->second > v ? 1 : 0;
            };

            // Start from the top assuming a new dependency cannot be added
            // without changing the dependent's version.
            //
            int r;
            return
              (r = cmp ("bbot",       BBOT_VERSION)) != 0 ? r :
              (r = cmp ("libbbot", LIBBBOT_VERSION)) != 0 ? r :
              (r = cmp ("libbpkg", LIBBPKG_VERSION)) != 0 ? r :
              (r = cmp ("libbutl", LIBBUTL_VERSION)) != 0 ? r : 0;
          };

          optional<bootstrapped_machine_manifest> bmm;
          if (te)
          {
            bmm = parse_manifest<bootstrapped_machine_manifest> (
              tp / "manifest", "bootstrapped machine");

            if (bmm->machine.id != mm.id)
            {
              l3 ([&]{trace << "re-bootstrapping " << tp << ": new machine";});
              te = false;
            }

            if (!tc_id.empty () && bmm->toolchain.id != tc_id)
            {
              l3 ([&]{trace << "re-bootstrapping " << tp << ": new toolchain";});
              te = false;
            }

            if (int i = compare_bbot (bmm->bootstrap))
            {
              if (i < 0)
              {
                l3 ([&]{trace << "re-bootstrapping " << tp << ": new bbot";});
                te = false;
              }
              else
              {
                l3 ([&]{trace << "ignoring " << tp << ": old bbot";});
                run_btrfs (trace, "subvolume", "delete", xp);
                break;
              }
            }

            if (!te)
              delete_t ();
          }
          else
            l3 ([&]{trace << "bootstrapping " << tp;});

          if (!te)
          {
            // Use the <name>-<toolchain>-<xxx> snapshot that we have made to
            // bootstrap the new machine. Then atomically rename it to
            // <name>-<toolchain>.
            //
            bmm = bootstrap_machine (xp, mm, move (bmm));

            if (!bmm)
            {
              l3 ([&]{trace << "ignoring " << tp << ": failed to bootstrap";});
              run_btrfs (trace, "subvolume", "delete", xp);
              break;
            }

            try
            {
              mvdir (xp, tp);
            }
            catch (const system_error& e)
            {
              fail << "unable to rename " << xp << " to " << tp;
            }

            l2 ([&]{trace << "bootstrapped " << bmm->machine.name;});

            // Check the bootstrapped bbot version as above and ignore this
            // machine if it's newer than us.
            //
            if (int i = compare_bbot (bmm->bootstrap))
            {
              assert (i > 0);
              l3 ([&]{trace << "ignoring " << tp << ": old bbot";});
              break;
            }
          }
          else
            run_btrfs (trace, "subvolume", "delete", xp);

          // Add the machine to the lists.
          //
          rm.push_back (move (*bmm));
          rd.push_back (move (tp));

          break;
        }
      }
    }
    catch (const system_error& e)
    {
      fail << "unable to iterate over " << vd << ": " << e << endf;
    }
  }

  return make_pair (move (rm), move (rd));
}
catch (const system_error& e)
{
  fail << "unable to iterate over " << machines << ": " << e << endf;
}

static result_manifest
perform_task (const dir_path& md,
              const bootstrapped_machine_manifest& mm,
              const task_manifest& tm)
try
{
  tracer trace ("perform_task");

  result_manifest r {
    tm.name,
    tm.version,
    result_status::abort,
    operation_results {}};

  if (ops.fake_build ())
    return r;

  // The overall plan is as follows:
  //
  // 1. Snapshot the (bootstrapped) machine.
  //
  // 2. Save the task manifest to the TFTP directory (to be accessed by the
  //    worker).
  //
  // 3. Start the TFTP server and the machine.
  //
  // 4. Serve TFTP requests while watching out for the result manifest.
  //
  // 5. Clean up (force the machine down and delete the snapshot).
  //

  // TFTP server mapping (server chroot is --tftp):
  //
  // GET requests to .../build/<name>/get/*
  // PUT requests to .../build/<name>/put/*
  //
  auto_rmdir arm ((dir_path (ops.tftp ()) /= "build") /= tc_name);

  dir_path gd (dir_path (arm.path ()) /= "get");
  dir_path pd (dir_path (arm.path ()) /= "put");

  try_mkdir_p (gd);
  try_mkdir_p (pd);

  path tf (gd / "manifest"); // Task manifest file.
  path rf (pd / "manifest"); // Result manifest file.

  serialize_manifest (tm, tf, "task");

  if (ops.fake_machine_specified ())
  {
    // Simply wait for the file to appear.
    //
    for (size_t i (0); !file_exists (rf); sleep (1))
      if (i++ % 10 == 0)
        l3 ([&]{trace << "waiting for result manifest";});

    r = parse_manifest<result_manifest> (rf, "result");
  }
  else
  {
    // <name>-<toolchain>-<xxx>
    //
    const dir_path xp (
      md.directory () /= path::traits::temp_name (md.leaf ().string ()));

    run_btrfs (trace, "subvolume", "snapshot", md, xp);

    string br ("br1"); // Using private bridge for now.

    // Start the TFTP server.
    //
    tftp_server tftpd ("Gr  ^/?(.+)$  /build/" + tc_name + "/get/\\1\n" +
                       "Pr  ^/?(.+)$  /build/" + tc_name + "/put/\\1\n");

    l3 ([&]{trace << "tftp server on port " << tftpd.port ();});

    // Start the machine.
    //
    unique_ptr<machine> m (
      start_machine (xp,
                     mm.machine,
                     mm.machine.mac,
                     br,
                     tftpd.port ()));

    // Note: the machine handling logic is similar to bootstrap.
    //
    {
      auto mg (
        make_exception_guard (
          [&m, &xp] ()
          {
            info << "trying to force machine " << xp << " down";
            try {m->forcedown ();} catch (const failed&) {}
          }));

      auto soft_fail = [&xp, &m, &r] (const char* msg, bool wait = true)
      {
        {
          diag_record dr (error);
          dr << msg << " for machine " << xp << ", suspending";
          m->print_info (dr);
        }
        m->suspend ();

        if (wait)
          m->wait ();

        return r;
      };

      // The first request should be the task manifest download. Wait for up
      // to 60 seconds for that to arrive. In a sense we use it as an
      // indication that the machine has booted and the worker process has
      // started.
      //
      size_t to;
      const size_t startup_to (60);
      const size_t build_to   (ops.build_timeout ());

      if (!tftpd.serve ((to = startup_to)))
        return soft_fail ("build startup timeout");

      l3 ([&]{trace << "completed startup in " << startup_to - to << "s";});

      // Next the worker builds things and then uploads the result manifest.
      // So on our side we serve TFTP requests while checking for the manifest
      // file.
      //
      for (to = build_to; to != 0 && !file_exists (rf); tftpd.serve (to)) ;

      if (to == 0)
        return soft_fail ("build timeout");

      l3 ([&]{trace << "completed build in " << build_to - to << "s";});

      // Parse the result manifest.
      //
      r = parse_manifest<result_manifest> (rf, "result");

      // If the build terminated abnormally, suspent the machine for
      // investigation (note that here we don't wait or return).
      //
      if (r.status == result_status::abnormal)
        soft_fail ("build terminated abnormally", false);

      // Force the machine down (there is no need wasting time on clean
      // shutdown since the next step is to drop the snapshot).
      //
      m->forcedown ();
    }

    run_btrfs (trace, "subvolume", "delete", xp);
  }

  // Update package name/version if the returned value as "unknown".
  //
  if (r.version == bpkg::version ("0"))
  {
    assert (r.status == result_status::abnormal);

    r.name = tm.name;
    r.version = tm.version;
  }

  return r;
}
catch (const system_error& e)
{
  fail << "build error: " << e << endf;
}

extern "C" void
handle_signal (int sig)
{
  switch (sig)
  {
  case SIGHUP:  exit (3); // Unimplemented feature.
  case SIGTERM: exit (0);
  default:      assert (false);
  }
}

int
main (int argc, char* argv[])
try
{
  cli::argv_scanner scan (argc, argv, true);
  ops.parse (scan);

  verb = ops.verbose ();

  if (ops.systemd_daemon ())
    systemd_diagnostics (true); // With critical errors.

  tracer trace ("main");

  uid = getuid ();
  uname = getpwuid (uid)->pw_name;

  {
    char buf[HOST_NAME_MAX + 1];

    if (gethostname (buf, sizeof (buf)) == -1)
      fail << "unable to obtain hostname: "
           << system_error (errno, generic_category ()); // Sanitize.

    hname = buf;
  }

  // On POSIX ignore SIGPIPE which is signaled to a pipe-writing process if
  // the pipe reading end is closed. Note that by default this signal
  // terminates a process. Also note that there is no way to disable this
  // behavior on a file descriptor basis or for the write() function call.
  //
  if (signal (SIGPIPE, SIG_IGN) == SIG_ERR)
    fail << "unable to ignore broken pipe (SIGPIPE) signal: "
         << system_error (errno, generic_category ()); // Sanitize.

  // Version.
  //
  if (ops.version ())
  {
    cout << "bbot-agent " << BBOT_VERSION_STR << endl
         << "libbbot " << LIBBBOT_VERSION_STR << endl
         << "libbutl " << LIBBUTL_VERSION_STR << endl
         << "Copyright (c) 2014-2017 Code Synthesis Ltd" << endl
         << "TBC; All rights reserved" << endl;

    return 0;
  }

  // Help.
  //
  if (ops.help ())
  {
    pager p ("bbot-agent help", false);
    print_bbot_agent_usage (p.stream ());

    // If the pager failed, assume it has issued some diagnostics.
    //
    return p.wait () ? 0 : 1;
  }

  tc_name = ops.toolchain_name ();
  tc_num  = ops.toolchain_num ();
  tc_id   = ops.toolchain_id ();


  // Controller URLs.
  //
  if (argc < 2 &&
      !ops.dump_machines () &&
      !ops.fake_request_specified ())
  {
    fail << "controller url expected" <<
      info << "run " << argv[0] << " --help for details";
  }

  strings controllers;

  for (int i (1); i != argc; ++i)
    controllers.push_back (argv[i]);

  // Handle SIGHUP and SIGTERM.
  //
  if (signal (SIGHUP,  &handle_signal) == SIG_ERR ||
      signal (SIGTERM, &handle_signal) == SIG_ERR)
    fail << "unable to set signal handler: "
         << system_error (errno, generic_category ()); // Sanitize.

  if (ops.systemd_daemon ())
  {
    diag_record dr;

    dr << info << "bbot agent " << BBOT_VERSION_STR <<
      info << "toolchain name " << tc_name <<
      info << "toolchain num  " << tc_num <<
      info << "toolchain id   " << tc_id <<
      info << "CPU(s)         " << ops.cpu () <<
      info << "RAM(kB)        " << ops.ram ();

    for (const string& u: controllers)
      dr << info << "controller url " << u;
  }

  // The work loop. The steps we go through are:
  //
  // 1. Enumerate the available machines, (re-)bootstrapping any if necessary.
  //
  // 2. Poll controller(s) for build tasks.
  //
  // 3. If no build tasks are available, go to #1 (after sleeping a bit).
  //
  // 4. If a build task is returned, do it, upload the result, and go to #1
  //    (immediately).
  //
  for (bool sleep (false);; ::sleep (sleep ? 60 : 0), sleep = false)
  {
    // Enumerate the machines.
    //
    auto mp (enumerate_machines (ops.machines ()));
    bootstrapped_machine_manifests& ms (mp.first);
    dir_paths& ds (mp.second);

    // Prepare task request.
    //
    // @@ TODO: key fingerprint.
    //
    task_request_manifest tq {hname, "", machine_header_manifests {}};

    for (const bootstrapped_machine_manifest& m: ms)
      tq.machines.emplace_back (m.machine.id,
                                m.machine.name,
                                m.machine.summary);

    if (ops.dump_machines ())
    {
      for (const machine_header_manifest& m: tq.machines)
        serialize_manifest (m, cout, "stdout", "machine");

      return 0;
    }

    if (tq.machines.empty ())
    {
      warn << "no build machines for toolchain " << tc_name;
      sleep = true;
      continue;
    }

    // Send task requests.
    //
    //
    string url;
    task_response_manifest tr;

    if (ops.fake_request_specified ())
    {
      auto t (parse_manifest<task_manifest> (ops.fake_request (), "task"));

      tr = task_response_manifest {
        "fake-session", // Dummy session.
        string (),      // Empty challange.
        url,            // Empty result URL.
        move (t)};

      url = "http://example.org";
    }
    else
    {
      for (const string& u: controllers)
      {
        try
        {
          http_curl c (trace,
                       path ("-"),
                       path ("-"),
                       curl::post,
                       u,
                       "--header", "Content-Type: text/manifest",
                       "--max-time", ops.request_timeout ());

          serialize_manifest (tq, c.out, u, "task request");
          c.out.close ();

          tr = parse_manifest<task_response_manifest> (
            c.in, u, "task response");
          c.in.close ();

          if (!c.wait ())
            throw_generic_error (EIO);
        }
        catch (const system_error& e)
        {
          error << "unable to request task from " << u << ": " << e;
          continue;
        }

        if (!tr.session.empty ()) // Got a task.
        {
          url = u;
          break;
        }
      }
    }

    if (tr.session.empty ()) // No task from any of the controllers.
    {
      sleep = true;
      continue;
    }

    // We have a build task.
    //
    // First find the index of the machine we were asked to use (and also
    // verify it is one of those we sent).
    //
    size_t i (0);
    for (const machine_header_manifest& m: tq.machines)
    {
      if (m.name == tr.task->machine)
        break;

      ++i;
    }

    if (i == ms.size ())
    {
      error << "task from " << url << " for unknown machine "
            << tr.task->machine;

      if (ops.dump_task ())
        return 0;

      continue;
    }

    task_manifest& t (*tr.task);

    if (ops.dump_task ())
    {
      serialize_manifest (t, cout, "stdout", "task");
      return 0;
    }

    // If we have our own repository certificate fingerprints, then use them
    // to replace what we have received from the controller.
    //
    if (!ops.trust ().empty ())
      t.trust = ops.trust ();

    const dir_path& d (ds[i]); // The -<toolchain> directory.
    const bootstrapped_machine_manifest& m (ms[i]);

    result_manifest r (perform_task (d, m, t));

    if (ops.dump_result ())
    {
      serialize_manifest (r, cout, "stdout", "result");
      return 0;
    }

    // Upload the result.
    //
    // @@ TODO challange
    //
    result_request_manifest rq {tr.session, "", move (r)};
    {
      const string& u (*tr.result_url);

      try
      {
        http_curl c (trace,
                     path ("-"),
                     nullfd,     // Not expecting any data in response.
                     curl::post,
                     u,
                     "--header", "Content-Type: text/manifest",
                     "--max-time", ops.request_timeout ());

        serialize_manifest (rq, c.out, u, "task request");
        c.out.close ();

        if (!c.wait ())
          throw_generic_error (EIO);
      }
      catch (const system_error& e)
      {
        error << "unable to upload result to " << u << ": " << e;
        continue;
      }
    }

    l2 ([&]{trace << "built " << t.name << '/' << t.version << " "
                  << "on " << t.machine << " "
                  << "for " << url;});
  }
}
catch (const failed&)
{
  return 1; // Diagnostics has already been issued.
}
catch (const cli::exception& e)
{
  error << e;
  return 1;
}