aboutsummaryrefslogtreecommitdiff
path: root/mod/mod-ci-github.cxx
blob: f89ce2c72e63a0cf4798e12e8b34b62fce11047a (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
1056
1057
1058
1059
1060
1061
1062
1063
1064
1065
1066
1067
1068
1069
1070
1071
1072
1073
1074
1075
1076
1077
1078
1079
1080
1081
1082
1083
1084
1085
1086
1087
1088
1089
1090
1091
1092
1093
1094
1095
1096
1097
1098
1099
1100
1101
1102
1103
1104
1105
1106
1107
1108
1109
1110
1111
1112
1113
1114
1115
1116
1117
1118
1119
1120
1121
1122
1123
1124
1125
1126
1127
1128
1129
1130
1131
1132
1133
1134
1135
1136
1137
1138
1139
1140
1141
1142
1143
1144
1145
1146
1147
1148
1149
1150
1151
1152
1153
1154
1155
1156
1157
1158
1159
1160
1161
1162
1163
1164
1165
1166
1167
1168
1169
1170
1171
1172
1173
1174
1175
1176
1177
1178
1179
1180
1181
1182
1183
1184
1185
1186
1187
1188
1189
1190
1191
1192
1193
1194
1195
1196
1197
1198
1199
1200
1201
1202
1203
1204
1205
1206
1207
1208
1209
1210
1211
1212
1213
1214
1215
1216
1217
1218
1219
1220
1221
1222
1223
1224
1225
1226
1227
1228
1229
1230
1231
1232
1233
1234
1235
1236
1237
1238
1239
1240
1241
1242
1243
1244
1245
1246
1247
1248
1249
1250
1251
1252
1253
1254
1255
1256
1257
1258
1259
1260
1261
1262
1263
1264
1265
1266
1267
1268
1269
1270
1271
1272
1273
1274
1275
1276
1277
1278
1279
1280
1281
1282
1283
1284
1285
1286
1287
1288
1289
1290
1291
1292
1293
1294
1295
1296
1297
1298
1299
1300
1301
1302
1303
1304
1305
1306
1307
1308
1309
1310
1311
1312
1313
1314
1315
1316
1317
1318
1319
1320
1321
1322
1323
1324
1325
1326
1327
1328
1329
1330
1331
1332
1333
1334
1335
1336
1337
1338
1339
1340
1341
1342
1343
1344
1345
1346
1347
1348
1349
1350
1351
1352
1353
1354
1355
1356
1357
1358
1359
1360
1361
1362
1363
1364
1365
1366
1367
1368
1369
1370
1371
1372
1373
1374
1375
1376
1377
1378
1379
1380
1381
1382
1383
1384
1385
1386
1387
1388
1389
1390
1391
1392
1393
1394
1395
1396
1397
1398
1399
1400
1401
1402
1403
1404
1405
1406
1407
1408
1409
1410
1411
1412
1413
1414
1415
1416
1417
1418
1419
1420
1421
1422
1423
1424
1425
1426
1427
1428
1429
1430
1431
1432
1433
1434
1435
1436
1437
1438
1439
1440
1441
1442
1443
1444
1445
1446
1447
1448
1449
1450
1451
1452
1453
1454
1455
1456
1457
1458
1459
1460
1461
1462
1463
1464
1465
1466
1467
1468
1469
1470
1471
1472
1473
1474
1475
1476
1477
1478
1479
1480
1481
1482
1483
1484
1485
1486
1487
1488
1489
1490
1491
1492
1493
1494
1495
1496
1497
1498
1499
1500
1501
1502
1503
1504
1505
1506
1507
1508
1509
1510
1511
// file      : mod/mod-ci-github.cxx -*- C++ -*-
// license   : MIT; see accompanying LICENSE file

#include <mod/mod-ci-github.hxx>

#include <libbutl/curl.hxx>
#include <libbutl/json/parser.hxx>
#include <libbutl/json/serializer.hxx>

#include <mod/jwt.hxx>
#include <mod/hmac.hxx>
#include <mod/module-options.hxx>

#include <stdexcept>

// @@ TODO
//
//    Building CI checks with a GitHub App
//    https://docs.github.com/en/apps/creating-github-apps/writing-code-for-a-github-app/building-ci-checks-with-a-github-app
//

// @@ TODO Best practices
//
//    Webhooks:
//    https://docs.github.com/en/webhooks/using-webhooks/best-practices-for-using-webhooks
//    https://docs.github.com/en/webhooks/using-webhooks/validating-webhook-deliveries
//
//    REST API:
//    https://docs.github.com/en/rest/using-the-rest-api/best-practices-for-using-the-rest-api?apiVersion=2022-11-28
//
//    Creating an App:
//    https://docs.github.com/en/apps/creating-github-apps/about-creating-github-apps/best-practices-for-creating-a-github-app
//
//    Use a webhook secret to ensure request is coming from Github. HMAC:
//    https://en.wikipedia.org/wiki/HMAC#Definition. A suitable implementation
//    is provided by OpenSSL.

using namespace std;
using namespace butl;
using namespace web;
using namespace brep::cli;

namespace brep
{
  // Operation failed, diagnostics has already been issued.
  //
  struct failed {};

  using namespace gh;

  ci_github::
  ci_github (tenant_service_map& tsm)
      : tenant_service_map_ (tsm)
  {
  }

  ci_github::
  ci_github (const ci_github& r, tenant_service_map& tsm)
      : handler (r),
        ci_start (r),
        options_ (r.initialized_ ? r.options_ : nullptr),
        tenant_service_map_ (tsm)
  {
  }

  void ci_github::
  init (scanner& s)
  {
    {
      shared_ptr<tenant_service_base> ts (
        dynamic_pointer_cast<tenant_service_base> (shared_from_this ()));

      assert (ts != nullptr); // By definition.

      tenant_service_map_["ci-github"] = move (ts);
    }

    options_ = make_shared<options::ci_github> (
      s, unknown_mode::fail, unknown_mode::fail);

    // Prepare for the CI requests handling, if configured.
    //
    if (options_->ci_github_app_webhook_secret_specified ())
    {
      ci_start::init (make_shared<options::ci_start> (*options_));
    }
  }

  bool ci_github::
  handle (request& rq, response&)
  {
    using namespace bpkg;

    HANDLER_DIAG;

    if (!options_->ci_github_app_webhook_secret_specified ())
      throw invalid_request (404, "GitHub CI request submission disabled");

    // Process headers.
    //
    // @@ TMP Shouldn't we also error<< in some of these header problem cases?
    //
    // @@ TMP From GitHub docs: "You can create webhooks that subscribe to the
    //        events listed on this page."
    //
    //        So it seems appropriate to generally use the term "event" (which
    //        we already do for the most part), and "webhook event" only when
    //        more context would be useful?
    //
    string event; // Webhook event.
    string hmac;  // Received HMAC.
    {
      bool content_type (false);

      for (const name_value& h: rq.headers ())
      {
        // HMAC authenticating this request. Note that it won't be present
        // unless a webhook secret has been set in the GitHub app's settings.
        //
        if (icasecmp (h.name, "x-hub-signature-256") == 0)
        {
          if (!h.value)
            throw invalid_request (400, "missing x-hub-signature-256 value");

          // Parse the x-hub-signature-256 header value. For example:
          //
          // sha256=5e82258...
          //
          // Check for the presence of the "sha256=" prefix and then strip it
          // to leave only the HMAC value.
          //
          if (h.value->find ("sha256=", 0, 7) == string::npos)
            throw invalid_request (400, "invalid x-hub-signature-256 value");

          hmac = h.value->substr (7);
        }
        // This event's UUID.
        //
        else if (icasecmp (h.name, "x-github-delivery") == 0)
        {
          // @@ TODO Check that delivery UUID has not been received before
          //         (replay attack).
        }
        else if (icasecmp (h.name, "content-type") == 0)
        {
          if (!h.value)
            throw invalid_request (400, "missing content-type value");

          if (icasecmp (*h.value, "application/json") != 0)
          {
            throw invalid_request (400,
                                   "invalid content-type value: '" + *h.value +
                                   '\'');
          }

          content_type = true;
        }
        // The webhook event.
        //
        else if (icasecmp (h.name, "x-github-event") == 0)
        {
          if (!h.value)
            throw invalid_request (400, "missing x-github-event value");

          event = *h.value;
        }
      }

      if (!content_type)
        throw invalid_request (400, "missing content-type header");

      if (event.empty ())
        throw invalid_request (400, "missing x-github-event header");

      if (hmac.empty ())
        throw invalid_request (400, "missing x-hub-signature-256 header");
    }

    // Read the entire request body into a buffer because we need to compute
    // an HMAC over it and then parse it as JSON. The alternative of reading
    // from the stream twice works out to be more complicated (see also @@
    // TODO item in web/server/module.hxx).
    //
    string body;
    {
      // Note that even though we may not need caching right now, we may later
      // (e.g., to support cancel) so let's just enable it right away.
      //
      size_t limit (128 * 1024);

      istream& is (rq.content (limit, limit));

      try
      {
        getline (is, body, '\0');
      }
      catch (const io_error& e)
      {
        fail << "unable to read request body: " << e;
      }
    }

    // Verify the received HMAC.
    //
    // Compute the HMAC value over the request body using the configured
    // webhook secret as key and compare it to the received HMAC.
    //
    try
    {
      string h (
        compute_hmac (*options_,
                      body.data (), body.size (),
                      options_->ci_github_app_webhook_secret ().c_str ()));

      if (!icasecmp (h, hmac))
      {
        string m ("computed HMAC does not match received HMAC");

        error << m;

        throw invalid_request (400, move (m));
      }
    }
    catch (const system_error& e)
    {
      fail << "unable to compute request HMAC: " << e;
    }

    // There is a webhook event (specified in the x-github-event header) and
    // each event contains a bunch of actions (specified in the JSON request
    // body).
    //
    // Note: "GitHub continues to add new event types and new actions to
    // existing event types." As a result we ignore known actions that we are
    // not interested in and log and ignore unknown actions. The thinking here
    // is that we want be "notified" of new actions at which point we can decide
    // whether to ignore them or to handle.
    //
    if (event == "check_suite")
    {
      check_suite_event cs;
      try
      {
        json::parser p (body.data (), body.size (), "check_suite event");

        cs = check_suite_event (p);
      }
      catch (const json::invalid_json_input& e)
      {
        string m ("malformed JSON in " + e.name + " request body");

        error << m << ", line: " << e.line << ", column: " << e.column
              << ", byte offset: " << e.position << ", error: " << e;

        throw invalid_request (400, move (m));
      }

      if (cs.action == "requested")
      {
        return handle_check_suite_request (move (cs));
      }
      else if (cs.action == "rerequested")
      {
        // Someone manually requested to re-run the check runs in this check
        // suite. Treat as a new request.
        //
        // @@ TMP Creating check_runs with same names as before will update
        //        the existing check_runs on GitHub (as opposed to creating
        //        new check_runs with the same names).
        //
        return handle_check_suite_request (move (cs));
      }
      else if (cs.action == "completed")
      {
        // GitHub thinks that "all the check runs in this check suite have
        // completed and a conclusion is available". Looks like this one we
        // ignore?
        //
        // @@ TODO What if our bookkeeping says otherwise? See conclusion
        //    field which includes timedout. Need to come back to this once
        //    have the "happy path" implemented.
        //
        return true;
      }
      else
      {
        // Ignore unknown actions by sending a 200 response with empty body
        // but also log as an error since we want to notice new actions.
        //
        error << "unknown action '" << cs.action << "' in check_suite event";

        return true;
      }
    }
    else if (event == "pull_request")
    {
      // @@ TODO

      throw invalid_request (501, "pull request events not implemented yet");
    }
    else
    {
      // Log to investigate.
      //
      error << "unexpected event '" << event << "'";

      throw invalid_request (400, "unexpected event: '" + event + "'");
    }
  }

  // Service data associated with the tenant/check suite.
  //
  // It is always a top-level JSON object and the first member is always the
  // schema version.
  //
  struct service_data
  {
    // The data schema version. Note: must be first member in the object.
    //
    uint64_t version = 1;

    // Check suite-global data.
    //
    installation_access_token installation_access;

    uint64_t installation_id;
    string repository_id; // GitHub-internal opaque repository id.
    string head_sha;

    // Construct from JSON.
    //
    // Throw invalid_argument if the schema version is not supported.
    //
    explicit
    service_data (const string& json);

    service_data (string iat_token,
                  timestamp iat_expires_at,
                  uint64_t installation_id,
                  string repository_id,
                  string head_sha);

    service_data () = default;

    // Serialize to JSON.
    //
    string
    json () const;
  };

  bool ci_github::
  handle_check_suite_request (check_suite_event cs)
  {
    HANDLER_DIAG;

    l3 ([&]{trace << "check_suite event { " << cs << " }";});

    optional<string> jwt (generate_jwt (trace, error));
    if (!jwt)
      throw failed ();

    optional<installation_access_token> iat (
        obtain_installation_access_token (cs.installation.id,
                                          move (*jwt),
                                          error));

    if (!iat)
      throw failed ();

    l3 ([&]{trace << "installation_access_token { " << *iat << " }";});

    // Submit the CI request.
    //
    repository_location rl (cs.repository.clone_url + '#' +
                                cs.check_suite.head_branch,
                            repository_type::git);

    string sd (service_data (move (iat->token),
                             iat->expires_at,
                             cs.installation.id,
                             move (cs.repository.node_id),
                             move (cs.check_suite.head_sha))
                   .json ());

    optional<start_result> r (
        start (error,
               warn,
               verb_ ? &trace : nullptr,
               tenant_service (move (cs.check_suite.node_id),
                               "ci-github",
                               move (sd)),
               move (rl),
               vector<package> {},
               nullopt, // client_ip
               nullopt  // user_agent
               ));

    if (!r)
      fail << "unable to submit CI request";

    return true;
  }

  // GraphQL serialization functions.
  //
  // The GraphQL spec:
  //   https://spec.graphql.org/
  //
  // The GitHub GraphQL API reference:
  //   https://docs.github.com/en/graphql/reference/
  //

  // Check that a string is a valid GraphQL name.
  //
  // GraphQL names can contain only alphanumeric characters and underscores
  // and cannot begin with a digit (so basically a C identifier).
  //
  // Return the name or throw invalid_argument if it is invalid.
  //
  static const string&
  gq_name (const string& v)
  {
    if (v.empty () || digit (v[0]))
      throw invalid_argument ("invalid GraphQL name: '" + v + '\'');

    for (char c: v)
    {
      if (!alnum (c) && c != '_')
      {
        throw invalid_argument ("invalid character in GraphQL name: '" + c +
                                '\'');
      }
    }

    return v;
  }

  // Serialize a string to GraphQL.
  //
  // Return the serialized string or throw invalid_argument if the string is
  // invalid.
  //
  static string
  gq_str (const string& v)
  {
    // GraphQL strings are the same as JSON strings so we use the JSON
    // serializer.
    //
    string b;
    json::buffer_serializer s (b);

    try
    {
      s.value (v);
    }
    catch (const json::invalid_json_output&)
    {
      throw invalid_argument ("invalid GraphQL string: '" + v + '\'');
    }

    return b;
  }

  // Serialize an int to GraphQL.
  //
#if 0
  static string
  gq_int (uint64_t v)
  {
    string b;
    json::buffer_serializer s (b);
    s.value (v);
    return b;
  }
#endif

  // Serialize a boolean to GraphQL.
  //
  static inline string
  gq_bool (bool v)
  {
    return v ? "true" : "false";
  }

  // Check that a string is a valid GraphQL enum value.
  //
  // GraphQL enum values can be any GraphQL name except for `true`, `false`,
  // or `null`.
  //
  // Return the enum value or throw invalid_argument if it is invalid.
  //
  static const string&
  gq_enum (const string& v)
  {
    if (v == "true" || v == "false" || v == "null")
      throw invalid_argument ("invalid GraphQL enum value: '" + v + '\'');

    return gq_name (v);
  }

  // Create a check_run name from a build.
  //
  static string
  check_run_name (const build& b)
  {
    return b.package_name.string () + '/'    +
           b.package_version.string () + '/' +
           b.target.string () + '/'          +
           b.target_config_name + '/'        +
           b.package_config_name + '/'       +
           b.toolchain_name + '/'            +
           b.toolchain_version.string ();
  }

  // Serialize `createCheckRun` mutations for one or more builds to GraphQL.
  //
  static string
  queue_check_runs (const string& ri, // Repository ID
                    const string& hs, // Head SHA
                    const vector<build>& bs)
  {
    ostringstream os;

    os << "mutation {"                                              << '\n';

    // Serialize a `createCheckRun` for each build.
    //
    for (size_t i (0); i != bs.size (); ++i)
    {
      const build& b (bs[i]);

      string al ("cr" + to_string (i)); // Field alias.

      // Check run name.
      //
      string nm (check_run_name (b));

      os << gq_name (al) << ":createCheckRun(input: {"              << '\n'
         << "  name: "         << gq_str (nm) << ','                << '\n'
         << "  repositoryId: " << gq_str (ri) << ','                << '\n'
         << "  headSha: "      << gq_str (hs) << ','                << '\n'
         << "  status: "       << gq_enum ("QUEUED")                << '\n'
         << "})"                                                    << '\n'
        // Specify the selection set (fields to be returned).
        //
         << "{"                                                     << '\n'
         << "  checkRun {"                                          << '\n'
         << "    id,"                                               << '\n'
         << "    name,"                                             << '\n'
         << "    status"                                            << '\n'
         << "  }"                                                   << '\n'
         << "}"                                                     << '\n';
    }

    os << "}"                                                       << '\n';

    return os.str ();
  }

  // Serialize a GraphQL operation (query/mutation) into a GraphQL request.
  //
  // This is essentially a JSON object with a "query" string member containing
  // the GraphQL operation. For example:
  //
  // { "query": "mutation { cr0:createCheckRun(... }" }
  //
  static string
  graphql_request (const string& o)
  {
    string b;
    json::buffer_serializer s (b);

    s.begin_object ();
    s.member ("query", o);
    s.end_object ();

    return b;
  }

  // Parse a response to a check_run GraphQL mutation such as `createCheckRun`
  // or `updateCheckRun`.
  //
  // Return the received check run objects or throw runtime_error if the
  // response indicated errors and invalid_json_input if the GitHub response
  // contained invalid JSON.
  //
  // The response format is defined in the GraphQL spec:
  // https://spec.graphql.org/October2021/#sec-Response.
  //
  // Example response:
  //
  // {
  //   "data": {
  //     "cr0": {
  //       "checkRun": {
  //         "id": "CR_kwDOLc8CoM8AAAAFQ5GqPg",
  //         "name": "libb2/0.98.1+2/x86_64-linux-gnu/linux_debian_12-gcc_13.1-O3/default/dev/0.17.0-a.1",
  //         "status": "QUEUED"
  //       }
  //     },
  //     "cr1": {
  //       "checkRun": {
  //         "id": "CR_kwDOLc8CoM8AAAAFQ5GqhQ",
  //         "name": "libb2/0.98.1+2/x86_64-linux-gnu/linux_debian_12-gcc_13.1/default/dev/0.17.0-a.1",
  //         "status": "QUEUED"
  //       }
  //     }
  //   }
  // }
  //
  // @@ TODO Handle response errors properly.
  //
  static vector<check_run>
  parse_check_runs_response (json::parser& p)
  {
    using event = json::event;

    auto throw_json = [&p] [[noreturn]] (const string& m)
    {
      throw json::invalid_json_input (
        p.input_name,
        p.line (), p.column (), p.position (),
        m);
    };

    vector<check_run> r;

    // True if the data/errors fields are present.
    //
    // Although the spec merely recommends that the `errors` field, if
    // present, comes before the `data` field, assume it always does because
    // letting the client parse data in the presence of field errors
    // (unexpected nulls) would not make sense.
    //
    bool dat (false), err (false);

    p.next_expect (event::begin_object);

    while (p.next_expect (event::name, event::end_object))
    {
      if (p.name () == "data")
      {
        dat = true;

        // Currently we're not handling fields that are null due to field
        // errors (see below for details) so don't parse any further.
        //
        if (err)
          break;

        p.next_expect (event::begin_object);

        // Parse the "cr0".."crN" members (field aliases).
        //
        while (p.next_expect (event::name, event::end_object))
        {
          // Parse `"crN": { "checkRun":`.
          //
          if (p.name () != "cr" + to_string (r.size ()))
            throw_json ("unexpected field alias: '" + p.name () + '\'');
          p.next_expect (event::begin_object);
          p.next_expect_name ("checkRun");

          r.emplace_back (p); // Parse the check_run object.

          p.next_expect (event::end_object); // Parse end of crN object.
        }

        if (r.empty ())
          throw_json ("data object is empty");
      }
      else if (p.name () == "errors")
      {
        // Don't stop parsing because the error semantics depends on whether
        // or not `data` is present.
        //
        err = true; // Handled below.
      }
      else
      {
        // The spec says the response will never contain any top-level fields
        // other than data, errors, and extensions.
        //
        if (p.name () != "extensions")
        {
          throw_json ("unexpected top-level GraphQL response field: '" +
                      p.name () + '\'');
        }

        p.next_expect_value_skip ();
      }
    }

    // If the `errors` field was present in the response, error(s) occurred
    // before or during execution of the operation.
    //
    // If the `data` field was not present the errors are request errors which
    // occur before execution and are typically the client's fault.
    //
    // If the `data` field was also present in the response the errors are
    // field errors which occur during execution and are typically the GraphQL
    // endpoint's fault, and some fields in `data` that should not be are
    // likely to be null.
    //
    if (err)
    {
      if (dat)
      {
        // @@ TODO: Consider parsing partial data?
        //
        throw runtime_error ("field error(s) received from GraphQL endpoint; "
                             "incomplete data received");
      }
      else
        throw runtime_error ("request error(s) received from GraphQL endpoint");
    }

    return r;
  }

  // Send a POST request to the GitHub API endpoint `ep`, parse GitHub's JSON
  // response into `rs` (only for 200 codes), and return the HTTP status code.
  //
  // The endpoint `ep` should not have a leading slash.
  //
  // Pass additional HTTP headers in `hdrs`. For example:
  //
  //   "HeaderName: header value"
  //
  // Throw invalid_argument if unable to parse the response headers,
  // invalid_json_input (derived from invalid_argument) if unable to parse the
  // response body, and system_error in other cases.
  //
  template <typename T>
  static uint16_t
  github_post (T& rs,
               const string& ep,
               const strings& hdrs,
               const string& body = "")
  {
    // Convert the header values to curl header option/value pairs.
    //
    strings hdr_opts;

    for (const string& h: hdrs)
    {
      hdr_opts.push_back ("--header");
      hdr_opts.push_back (h);
    }

    // Run curl.
    //
    try
    {
      // Pass --include to print the HTTP status line (followed by the response
      // headers) so that we can get the response status code.
      //
      // Suppress the --fail option which causes curl to exit with status 22
      // in case of an error HTTP response status code (>= 400) otherwise we
      // can't get the status code.
      //
      // Note that butl::curl also adds --location to make curl follow redirects
      // (which is recommended by GitHub).
      //
      // The API version `2022-11-28` is the only one currently supported. If
      // the X-GitHub-Api-Version header is not passed this version will be
      // chosen by default.
      //
      fdpipe errp (fdopen_pipe ()); // stderr pipe.

      curl c (path ("-"), // Read input from curl::out.
              path ("-"), // Write response to curl::in.
              process::pipe (errp.in.get (), move (errp.out)),
              curl::post,
              curl::flags::no_fail,
              "https://api.github.com/" + ep,
              "--no-fail", // Don't fail if response status code >= 400.
              "--include", // Output response headers for status code.
              "--header", "Accept: application/vnd.github+json",
              "--header", "X-GitHub-Api-Version: 2022-11-28",
              move (hdr_opts));

      ifdstream err (move (errp.in));

      // Parse the HTTP response.
      //
      int sc; // Status code.
      try
      {
        // Note: re-open in/out so that they get automatically closed on
        // exception.
        //
        ifdstream in (c.in.release (), fdstream_mode::skip);
        ofdstream out (c.out.release ());

        // Write request body to out.
        //
        if (!body.empty ())
          out << body;
        out.close ();

        sc = curl::read_http_status (in).code; // May throw invalid_argument.

        // Parse the response body if the status code is in the 200 range.
        //
        if (sc >= 200 && sc < 300)
        {
          // Use endpoint name as input name (useful to have it propagated
          // in exceptions).
          //
          json::parser p (in, ep /* name */);
          rs = T (p);
        }

        in.close ();
      }
      catch (const io_error& e)
      {
        // If the process exits with non-zero status, assume the IO error is due
        // to that and fall through.
        //
        if (c.wait ())
        {
          throw_generic_error (
            e.code ().value (),
            (string ("unable to read curl stdout: ") + e.what ()).c_str ());
        }
      }
      catch (const json::invalid_json_input&)
      {
        // If the process exits with non-zero status, assume the JSON error is
        // due to that and fall through.
        //
        if (c.wait ())
          throw;
      }

      if (!c.wait ())
      {
        string et (err.read_text ());
        throw_generic_error (EINVAL,
                             ("non-zero curl exit status: " + et).c_str ());
      }

      err.close ();

      return sc;
    }
    catch (const process_error& e)
    {
      throw_generic_error (
        e.code ().value (),
        (string ("unable to execute curl:") + e.what ()).c_str ());
    }
    catch (const io_error& e)
    {
      // Unable to read diagnostics from stderr.
      //
      throw_generic_error (
        e.code ().value (),
        (string ("unable to read curl stderr : ") + e.what ()).c_str ());
    }
  }

  function<optional<string> (const brep::tenant_service&)> brep::ci_github::
  build_queued (const tenant_service& ts,
                const vector<build>& bs,
                optional<build_state> /* initial_state */,
                const build_queued_hints&,
                const diag_epilogue& log_writer) const noexcept
  {
    NOTIFICATION_DIAG (log_writer);

    service_data sd;
    try
    {
      sd = service_data (*ts.data);
    }
    catch (const invalid_argument& e)
    {
      error << "failed to parse service data: " << e;
      return nullptr;
    }

    // Queue a check_run for each build.
    //
    string rq (graphql_request (
        queue_check_runs (sd.repository_id, sd.head_sha, bs)));

    // Response type which parses a GraphQL response containing multiple
    // check_run objects.
    //
    struct resp
    {
      vector<check_run> check_runs; // Received check runs.

      resp (json::parser& p) : check_runs (parse_check_runs_response (p)) {}

      resp () = default;
    } rs;

    // Get a new installation access token if the current one has expired.
    //
    optional<installation_access_token> new_iat;

    if (system_clock::now () > sd.installation_access.expires_at)
    {
      optional<string> jwt (generate_jwt (trace, error));
      if (!jwt)
        return nullptr;

      new_iat = obtain_installation_access_token (sd.installation_id,
                                                  move (*jwt),
                                                  error);
      if (!new_iat)
        return nullptr;
    }

    try
    {
      uint16_t sc (github_post (
          rs,
          "graphql", // API Endpoint.
          strings {"Authorization: Bearer " +
                   (new_iat ? *new_iat : sd.installation_access).token},
          move (rq)));

      if (sc != 200)
      {
        error << "failed to queue check runs: "
              << "error HTTP response status " << sc;
        return nullptr;
      }
    }
    catch (const json::invalid_json_input& e)
    {
      // Note: e.name is the GitHub API endpoint.
      //
      error << "malformed JSON in response from " << e.name << ", line: "
            << e.line << ", column: " << e.column << ", byte offset: "
            << e.position << ", error: " << e;
      return nullptr;
    }
    catch (const invalid_argument& e)
    {
      error << "malformed header(s) in response: " << e;
      return nullptr;
    }
    catch (const system_error& e)
    {
      error << "unable to queue check runs (errno=" << e.code ()
            << "): " << e.what ();
      return nullptr;
    }
    catch (const runtime_error& e) // From parse_check_runs_response().
    {
      // GitHub response contained error(s) (could be ours or theirs at this
      // point).
      //
      error << "unable to queue check runs: " << e;
      return nullptr;
    }

    if (rs.check_runs.size () != bs.size ())
    {
      error << "unexpected number of check_run objects in response";
      return nullptr;
    }

    // Validate the check runs in the response against the builds.
    //
    for (size_t i (0); i != rs.check_runs.size (); ++i)
    {
      const build& b (bs[i]);
      const check_run& cr (rs.check_runs[i]);

      if (cr.name != check_run_name (b))
      {
        error << "unexpected check_run name: '" + cr.name + '\'';
        return nullptr;
      }
      else if (cr.status != "QUEUED")
      {
        error << "unexpected check_run status: '" + cr.status + '\'';
        return nullptr;
      }

      l3 ([&]{trace << "check_run { " << cr << " }";});
    }

    return [iat = move (new_iat)] (const tenant_service& ts) -> optional<string>
    {
      service_data sd;
      try
      {
        sd = service_data (*ts.data);
      }
      catch (const invalid_argument& e)
      {
        // @@ TODO: error<<....
        //
        //          It looks like saving log_writer in this lambda would be
        //          safe, but not 100% sure. Also, the log entry will say
        //          build_queued() which is not entirely accurate. Maybe OK
        //          for a lambda but what about a real function?
        //
        // error << "failed to parse service data: " << e;
        return nullopt;
      }

      if (iat)
        sd.installation_access = move (*iat);

      return sd.json ();
    };
  }

  function<optional<string> (const brep::tenant_service&)> brep::ci_github::
  build_building (const tenant_service&, const build&,
                  const diag_epilogue& /* log_writer */) const noexcept
  {
    return nullptr;
  }

  function<optional<string> (const brep::tenant_service&)> brep::ci_github::
  build_built (const tenant_service&, const build&,
               const diag_epilogue& /* log_writer */) const noexcept
  {
    return nullptr;
  }

  optional<string> ci_github::
  generate_jwt (const basic_mark& trace,
                const basic_mark& error) const
  {
    string jwt;
    try
    {
      // Set token's "issued at" time 60 seconds in the past to combat clock
      // drift (as recommended by GitHub).
      //
      jwt = brep::generate_jwt (
          *options_,
          options_->ci_github_app_private_key (),
          to_string (options_->ci_github_app_id ()),
          chrono::seconds (options_->ci_github_jwt_validity_period ()),
          chrono::seconds (60));

      l3 ([&]{trace << "JWT: " << jwt;});
    }
    catch (const system_error& e)
    {
      error << "unable to generate JWT (errno=" << e.code () << "): " << e;
      return nullopt;
    }

    return jwt;
  }

  // There are three types of GitHub API authentication:
  //
  //   1) Authenticating as an app. Used to access parts of the API concerning
  //      the app itself such as getting the list of installations. (Need to
  //      authenticate as an app as part of authenticating as an app
  //      installation.)
  //
  //   2) Authenticating as an app installation (on a user or organisation
  //      account). Used to access resources belonging to the user/repository
  //      or organisation the app is installed in.
  //
  //   3) Authenticating as a user. Used to perform actions as the user.
  //
  // We need to authenticate as an app installation (2).
  //
  // How to authenticate as an app installation
  //
  // Reference:
  // https://docs.github.com/en/apps/creating-github-apps/authenticating-with-a-github-app/authenticating-as-a-github-app-installation
  //
  // The final authentication token we need is an installation access token
  // (IAT), valid for one hour, which we will pass in the `Authentication`
  // header of our Github API requests:
  //
  //   Authorization: Bearer <INSTALLATION_ACCESS_TOKEN>
  //
  // To generate an IAT:
  //
  // - Generate a JSON Web Token (JWT)
  //
  // - Get the installation ID. This will be included in the webhook request
  //   in our case
  //
  // - Send a POST to /app/installations/<INSTALLATION_ID>/access_tokens which
  //   includes the JWT (`Authorization: Bearer <JWT>`). The response will
  //   include the IAT. Can pass the name of the repository included in the
  //   webhook request to restrict access, otherwise we get access to all
  //   repos covered by the installation if installed on an organisation for
  //   example.
  //
  optional<installation_access_token>
  ci_github::obtain_installation_access_token (uint64_t iid,
                                               string jwt,
                                               const basic_mark& error) const
  {
    installation_access_token iat;
    try
    {
      // API endpoint.
      //
      string ep ("app/installations/" + to_string (iid) + "/access_tokens");

      int sc (github_post (iat, ep, strings {"Authorization: Bearer " + jwt}));

      // Possible response status codes from the access_tokens endpoint:
      //
      // 201 Created
      // 401 Requires authentication
      // 403 Forbidden
      // 404 Resource not found
      // 422 Validation failed, or the endpoint has been spammed.
      //
      // Note that the payloads of non-201 status codes are undocumented.
      //
      if (sc != 201)
      {
        error << "unable to get installation access token: "
              << "error HTTP response status " << sc;
        return nullopt;
      }

      // Create a clock drift safety window.
      //
      iat.expires_at -= chrono::minutes (5);
    }
    catch (const json::invalid_json_input& e)
    {
      // Note: e.name is the GitHub API endpoint.
      //
      error << "malformed JSON in response from " << e.name << ", line: "
            << e.line << ", column: " << e.column << ", byte offset: "
            << e.position << ", error: " << e;
      return nullopt;
    }
    catch (const invalid_argument& e)
    {
      error << "malformed header(s) in response: " << e;
      return nullopt;
    }
    catch (const system_error& e)
    {
      error << "unable to get installation access token (errno=" << e.code ()
            << "): " << e.what ();
      return nullopt;
    }

    return iat;
  }

  static string
  to_iso8601 (timestamp t)
  {
    return butl::to_string (t,
                            "%Y-%m-%dT%TZ",
                            false /* special */,
                            false /* local */);
  }

  static timestamp
  from_iso8601 (const string& s)
  {
    return butl::from_string (s.c_str (), "%Y-%m-%dT%TZ", false /* local */);
  }

  using event = json::event;

  service_data::
  service_data (const string& json)
  {
    json::parser p (json.data (), json.size (), "service_data");

    p.next_expect (event::begin_object);

    // Throw if the schema version is not supported.
    //
    version = p.next_expect_member_number<uint64_t> ("version");
    if (version != 1)
    {
      throw invalid_argument ("unsupported service_data schema version: " +
                              to_string (version));
    }

    // Installation access token.
    //
    p.next_expect_member_object ("iat");
    installation_access.token = p.next_expect_member_string ("tok");
    installation_access.expires_at =
        from_iso8601 (p.next_expect_member_string ("exp"));
    p.next_expect (event::end_object);

    installation_id = p.next_expect_member_number<uint64_t> ("iid");
    repository_id = p.next_expect_member_string ("rid");
    head_sha = p.next_expect_member_string ("hs");

    p.next_expect (event::end_object);
  }

  service_data::
  service_data (string iat_tok,
                timestamp iat_ea,
                uint64_t iid,
                string rid,
                string hs)
      : installation_access (move (iat_tok), iat_ea),
        installation_id (iid),
        repository_id (move (rid)),
        head_sha (move (hs))
  {
  }

  string service_data::
  json () const
  {
    string b;
    json::buffer_serializer s (b);

    s.begin_object ();

    s.member ("version", 1);

    // Installation access token.
    //
    s.member_begin_object ("iat");
    s.member ("tok", installation_access.token);
    s.member ("exp", to_iso8601 (installation_access.expires_at));
    s.end_object ();

    s.member ("iid", installation_id);
    s.member ("rid", repository_id);
    s.member ("hs", head_sha);

    s.end_object ();

    return b;
  }

  // The rest is GitHub request/response type parsing and printing.
  //

  // Throw invalid_json_input when a required member `m` is missing from a
  // JSON object `o`.
  //
  [[noreturn]] static void
  missing_member (const json::parser& p, const char* o, const char* m)
  {
    throw json::invalid_json_input (
      p.input_name,
      p.line (), p.column (), p.position (),
      o + string (" object is missing member '") + m + '\'');
  }

  // check_suite
  //
  gh::check_suite::
  check_suite (json::parser& p)
  {
    p.next_expect (event::begin_object);

    bool ni (false), hb (false), hs (false), bf (false), at (false);

    // Skip unknown/uninteresting members.
    //
    while (p.next_expect (event::name, event::end_object))
    {
      auto c = [&p] (bool& v, const char* s)
      {
        return p.name () == s ? (v = true) : false;
      };

      if      (c (ni, "node_id"))     node_id = p.next_expect_string ();
      else if (c (hb, "head_branch")) head_branch = p.next_expect_string ();
      else if (c (hs, "head_sha"))    head_sha = p.next_expect_string ();
      else if (c (bf, "before"))      before = p.next_expect_string ();
      else if (c (at, "after"))       after = p.next_expect_string ();
      else p.next_expect_value_skip ();
    }

    if (!ni) missing_member (p, "check_suite", "node_id");
    if (!hb) missing_member (p, "check_suite", "head_branch");
    if (!hs) missing_member (p, "check_suite", "head_sha");
    if (!bf) missing_member (p, "check_suite", "before");
    if (!at) missing_member (p, "check_suite", "after");
  }

  ostream&
  gh::operator<< (ostream& os, const check_suite& cs)
  {
    os << "node_id: " << cs.node_id
       << ", head_branch: " << cs.head_branch
       << ", head_sha: " << cs.head_sha
       << ", before: " << cs.before
       << ", after: " << cs.after;

    return os;
  }

  // check_run
  //
  gh::check_run::
  check_run (json::parser& p)
  {
    p.next_expect (event::begin_object);

    bool ni (false), nm (false), st (false);

    while (p.next_expect (event::name, event::end_object))
    {
      auto c = [&p] (bool& v, const char* s)
      {
        return p.name () == s ? (v = true) : false;
      };

      if      (c (ni, "id"))     node_id = p.next_expect_string ();
      else if (c (nm, "name"))   name = p.next_expect_string ();
      else if (c (st, "status")) status = p.next_expect_string ();
    }

    if (!ni) missing_member (p, "check_run", "id");
    if (!nm) missing_member (p, "check_run", "name");
    if (!st) missing_member (p, "check_run", "status");
  }

  ostream&
  gh::operator<< (ostream& os, const check_run& cr)
  {
    os << "node_id: " << cr.node_id
       << ", name: " << cr.name
       << ", status: " << cr.status;

    return os;
  }

  // repository
  //
  gh::repository::
  repository (json::parser& p)
  {
    p.next_expect (event::begin_object);

    bool ni (false), nm (false), fn (false), db (false), cu (false);

    // Skip unknown/uninteresting members.
    //
    while (p.next_expect (event::name, event::end_object))
    {
      auto c = [&p] (bool& v, const char* s)
      {
        return p.name () == s ? (v = true) : false;
      };

      if      (c (ni, "node_id"))        node_id = p.next_expect_string ();
      else if (c (nm, "name"))           name = p.next_expect_string ();
      else if (c (fn, "full_name"))      full_name = p.next_expect_string ();
      else if (c (db, "default_branch")) default_branch = p.next_expect_string ();
      else if (c (cu, "clone_url"))      clone_url = p.next_expect_string ();
      else p.next_expect_value_skip ();
    }

    if (!ni) missing_member (p, "repository", "node_id");
    if (!nm) missing_member (p, "repository", "name");
    if (!fn) missing_member (p, "repository", "full_name");
    if (!db) missing_member (p, "repository", "default_branch");
    if (!cu) missing_member (p, "repository", "clone_url");
  }

  ostream&
  gh::operator<< (ostream& os, const repository& rep)
  {
    os << "node_id: " << rep.node_id
       << ", name: " << rep.name
       << ", full_name: " << rep.full_name
       << ", default_branch: " << rep.default_branch
       << ", clone_url: " << rep.clone_url;

    return os;
  }

  // installation
  //
  gh::installation::
  installation (json::parser& p)
  {
    p.next_expect (event::begin_object);

    bool i (false);

    // Skip unknown/uninteresting members.
    //
    while (p.next_expect (event::name, event::end_object))
    {
      auto c = [&p] (bool& v, const char* s)
      {
        return p.name () == s ? (v = true) : false;
      };

      if (c (i, "id")) id = p.next_expect_number<uint64_t> ();
      else p.next_expect_value_skip ();
    }

    if (!i) missing_member (p, "installation", "id");
  }

  ostream&
  gh::operator<< (ostream& os, const installation& i)
  {
    os << "id: " << i.id;

    return os;
  }

  // check_suite_event
  //
  gh::check_suite_event::
  check_suite_event (json::parser& p)
  {
    p.next_expect (event::begin_object);

    bool ac (false), cs (false), rp (false), in (false);

    // Skip unknown/uninteresting members.
    //
    while (p.next_expect (event::name, event::end_object))
    {
      auto c = [&p] (bool& v, const char* s)
      {
        return p.name () == s ? (v = true) : false;
      };

      if      (c (ac, "action"))       action = p.next_expect_string ();
      else if (c (cs, "check_suite"))  check_suite = gh::check_suite (p);
      else if (c (rp, "repository"))   repository = gh::repository (p);
      else if (c (in, "installation")) installation = gh::installation (p);
      else p.next_expect_value_skip ();
    }

    if (!ac) missing_member (p, "check_suite_event", "action");
    if (!cs) missing_member (p, "check_suite_event", "check_suite");
    if (!rp) missing_member (p, "check_suite_event", "repository");
    if (!in) missing_member (p, "check_suite_event", "installation");
  }

  ostream&
  gh::operator<< (ostream& os, const check_suite_event& cs)
  {
    os << "action: " << cs.action;
    os << ", check_suite { " << cs.check_suite << " }";
    os << ", repository { "  << cs.repository << " }";
    os << ", installation { " << cs.installation << " }";

    return os;
  }

  // installation_access_token
  //
  // Example JSON:
  //
  // {
  //   "token": "ghs_Py7TPcsmsITeVCAWeVtD8RQs8eSos71O5Nzp",
  //   "expires_at": "2024-02-15T16:16:38Z",
  //   ...
  // }
  //
  gh::installation_access_token::
  installation_access_token (json::parser& p)
  {
    p.next_expect (event::begin_object);

    bool tk (false), ea (false);

    // Skip unknown/uninteresting members.
    //
    while (p.next_expect (event::name, event::end_object))
    {
      auto c = [&p] (bool& v, const char* s)
      {
        return p.name () == s ? (v = true) : false;
      };

      if      (c (tk, "token"))      token = p.next_expect_string ();
      else if (c (ea, "expires_at")) expires_at = from_iso8601 (p.next_expect_string ());
      else p.next_expect_value_skip ();
    }

    if (!tk) missing_member (p, "installation_access_token", "token");
    if (!ea) missing_member (p, "installation_access_token", "expires_at");
  }

  gh::installation_access_token::installation_access_token (const string& tk,
                                                            timestamp ea)
      : token (tk), expires_at (ea)
  {
  }

  ostream&
  gh::operator<< (ostream& os, const installation_access_token& t)
  {
    os << "token: " << t.token << ", expires_at: ";
    butl::operator<< (os, t.expires_at);

    return os;
  }
}