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
1512
1513
1514
1515
1516
1517
1518
1519
1520
1521
1522
1523
1524
1525
1526
1527
1528
1529
1530
1531
1532
1533
1534
1535
1536
1537
1538
1539
1540
1541
1542
1543
1544
1545
1546
1547
1548
1549
1550
1551
1552
1553
1554
1555
1556
1557
1558
1559
1560
1561
1562
1563
1564
1565
1566
1567
1568
1569
1570
1571
1572
1573
1574
1575
1576
1577
1578
1579
1580
1581
1582
1583
1584
1585
1586
1587
1588
1589
1590
1591
1592
1593
1594
1595
1596
1597
1598
1599
1600
1601
1602
1603
1604
1605
1606
1607
1608
1609
1610
/// Defines the HTTP configuration for an API service. It contains a list of
/// \[HttpRule][google.api.HttpRule\], each specifying the mapping of an RPC method
/// to one or more HTTP REST API methods.
/// # gRPC Transcoding
///
/// gRPC Transcoding is a feature for mapping between a gRPC method and one or
/// more HTTP REST endpoints. It allows developers to build a single API service
/// that supports both gRPC APIs and REST APIs. Many systems, including [Google
/// APIs](<https://github.com/googleapis/googleapis>),
/// [Cloud Endpoints](<https://cloud.google.com/endpoints>), [gRPC
/// Gateway](<https://github.com/grpc-ecosystem/grpc-gateway>),
/// and \[Envoy\](<https://github.com/envoyproxy/envoy>) proxy support this feature
/// and use it for large scale production services.
///
/// `HttpRule` defines the schema of the gRPC/REST mapping. The mapping specifies
/// how different portions of the gRPC request message are mapped to the URL
/// path, URL query parameters, and HTTP request body. It also controls how the
/// gRPC response message is mapped to the HTTP response body. `HttpRule` is
/// typically specified as an `google.api.http` annotation on the gRPC method.
///
/// Each mapping specifies a URL path template and an HTTP method. The path
/// template may refer to one or more fields in the gRPC request message, as long
/// as each field is a non-repeated field with a primitive (non-message) type.
/// The path template controls how fields of the request message are mapped to
/// the URL path.
///
/// Example:
///
/// service Messaging {
/// rpc GetMessage(GetMessageRequest) returns (Message) {
/// option (google.api.http) = {
/// get: "/v1/{name=messages/*}"
/// };
/// }
/// }
/// message GetMessageRequest {
/// string name = 1; // Mapped to URL path.
/// }
/// message Message {
/// string text = 1; // The resource content.
/// }
///
/// This enables an HTTP REST to gRPC mapping as below:
///
/// HTTP | gRPC
/// -----|-----
/// `GET /v1/messages/123456` | `GetMessage(name: "messages/123456")`
///
/// Any fields in the request message which are not bound by the path template
/// automatically become HTTP query parameters if there is no HTTP request body.
/// For example:
///
/// service Messaging {
/// rpc GetMessage(GetMessageRequest) returns (Message) {
/// option (google.api.http) = {
/// get:"/v1/messages/{message_id}"
/// };
/// }
/// }
/// message GetMessageRequest {
/// message SubMessage {
/// string subfield = 1;
/// }
/// string message_id = 1; // Mapped to URL path.
/// int64 revision = 2; // Mapped to URL query parameter `revision`.
/// SubMessage sub = 3; // Mapped to URL query parameter `sub.subfield`.
/// }
///
/// This enables a HTTP JSON to RPC mapping as below:
///
/// HTTP | gRPC
/// -----|-----
/// `GET /v1/messages/123456?revision=2&sub.subfield=foo` |
/// `GetMessage(message_id: "123456" revision: 2 sub: SubMessage(subfield:
/// "foo"))`
///
/// Note that fields which are mapped to URL query parameters must have a
/// primitive type or a repeated primitive type or a non-repeated message type.
/// In the case of a repeated type, the parameter can be repeated in the URL
/// as `...?param=A¶m=B`. In the case of a message type, each field of the
/// message is mapped to a separate parameter, such as
/// `...?foo.a=A&foo.b=B&foo.c=C`.
///
/// For HTTP methods that allow a request body, the `body` field
/// specifies the mapping. Consider a REST update method on the
/// message resource collection:
///
/// service Messaging {
/// rpc UpdateMessage(UpdateMessageRequest) returns (Message) {
/// option (google.api.http) = {
/// patch: "/v1/messages/{message_id}"
/// body: "message"
/// };
/// }
/// }
/// message UpdateMessageRequest {
/// string message_id = 1; // mapped to the URL
/// Message message = 2; // mapped to the body
/// }
///
/// The following HTTP JSON to RPC mapping is enabled, where the
/// representation of the JSON in the request body is determined by
/// protos JSON encoding:
///
/// HTTP | gRPC
/// -----|-----
/// `PATCH /v1/messages/123456 { "text": "Hi!" }` | `UpdateMessage(message_id:
/// "123456" message { text: "Hi!" })`
///
/// The special name `*` can be used in the body mapping to define that
/// every field not bound by the path template should be mapped to the
/// request body. This enables the following alternative definition of
/// the update method:
///
/// service Messaging {
/// rpc UpdateMessage(Message) returns (Message) {
/// option (google.api.http) = {
/// patch: "/v1/messages/{message_id}"
/// body: "*"
/// };
/// }
/// }
/// message Message {
/// string message_id = 1;
/// string text = 2;
/// }
///
///
/// The following HTTP JSON to RPC mapping is enabled:
///
/// HTTP | gRPC
/// -----|-----
/// `PATCH /v1/messages/123456 { "text": "Hi!" }` | `UpdateMessage(message_id:
/// "123456" text: "Hi!")`
///
/// Note that when using `*` in the body mapping, it is not possible to
/// have HTTP parameters, as all fields not bound by the path end in
/// the body. This makes this option more rarely used in practice when
/// defining REST APIs. The common usage of `*` is in custom methods
/// which don't use the URL at all for transferring data.
///
/// It is possible to define multiple HTTP methods for one RPC by using
/// the `additional_bindings` option. Example:
///
/// service Messaging {
/// rpc GetMessage(GetMessageRequest) returns (Message) {
/// option (google.api.http) = {
/// get: "/v1/messages/{message_id}"
/// additional_bindings {
/// get: "/v1/users/{user_id}/messages/{message_id}"
/// }
/// };
/// }
/// }
/// message GetMessageRequest {
/// string message_id = 1;
/// string user_id = 2;
/// }
///
/// This enables the following two alternative HTTP JSON to RPC mappings:
///
/// HTTP | gRPC
/// -----|-----
/// `GET /v1/messages/123456` | `GetMessage(message_id: "123456")`
/// `GET /v1/users/me/messages/123456` | `GetMessage(user_id: "me" message_id:
/// "123456")`
///
/// ## Rules for HTTP mapping
///
/// 1. Leaf request fields (recursive expansion nested messages in the request
/// message) are classified into three categories:
/// - Fields referred by the path template. They are passed via the URL path.
/// - Fields referred by the \[HttpRule.body][google.api.HttpRule.body\]. They
/// are passed via the HTTP
/// request body.
/// - All other fields are passed via the URL query parameters, and the
/// parameter name is the field path in the request message. A repeated
/// field can be represented as multiple query parameters under the same
/// name.
/// 2. If \[HttpRule.body][google.api.HttpRule.body\] is "*", there is no URL
/// query parameter, all fields
/// are passed via URL path and HTTP request body.
/// 3. If \[HttpRule.body][google.api.HttpRule.body\] is omitted, there is no HTTP
/// request body, all
/// fields are passed via URL path and URL query parameters.
///
/// ### Path template syntax
///
/// Template = "/" Segments [ Verb ] ;
/// Segments = Segment { "/" Segment } ;
/// Segment = "*" | "**" | LITERAL | Variable ;
/// Variable = "{" FieldPath [ "=" Segments ] "}" ;
/// FieldPath = IDENT { "." IDENT } ;
/// Verb = ":" LITERAL ;
///
/// The syntax `*` matches a single URL path segment. The syntax `**` matches
/// zero or more URL path segments, which must be the last part of the URL path
/// except the `Verb`.
///
/// The syntax `Variable` matches part of the URL path as specified by its
/// template. A variable template must not contain other variables. If a variable
/// matches a single path segment, its template may be omitted, e.g. `{var}`
/// is equivalent to `{var=*}`.
///
/// The syntax `LITERAL` matches literal text in the URL path. If the `LITERAL`
/// contains any reserved character, such characters should be percent-encoded
/// before the matching.
///
/// If a variable contains exactly one path segment, such as `"{var}"` or
/// `"{var=*}"`, when such a variable is expanded into a URL path on the client
/// side, all characters except `\[-_.~0-9a-zA-Z\]` are percent-encoded. The
/// server side does the reverse decoding. Such variables show up in the
/// [Discovery
/// Document](<https://developers.google.com/discovery/v1/reference/apis>) as
/// `{var}`.
///
/// If a variable contains multiple path segments, such as `"{var=foo/*}"`
/// or `"{var=**}"`, when such a variable is expanded into a URL path on the
/// client side, all characters except `\[-_.~/0-9a-zA-Z\]` are percent-encoded.
/// The server side does the reverse decoding, except "%2F" and "%2f" are left
/// unchanged. Such variables show up in the
/// [Discovery
/// Document](<https://developers.google.com/discovery/v1/reference/apis>) as
/// `{+var}`.
///
/// ## Using gRPC API Service Configuration
///
/// gRPC API Service Configuration (service config) is a configuration language
/// for configuring a gRPC service to become a user-facing product. The
/// service config is simply the YAML representation of the `google.api.Service`
/// proto message.
///
/// As an alternative to annotating your proto file, you can configure gRPC
/// transcoding in your service config YAML files. You do this by specifying a
/// `HttpRule` that maps the gRPC method to a REST endpoint, achieving the same
/// effect as the proto annotation. This can be particularly useful if you
/// have a proto that is reused in multiple services. Note that any transcoding
/// specified in the service config will override any matching transcoding
/// configuration in the proto.
///
/// Example:
///
/// http:
/// rules:
/// # Selects a gRPC method and applies HttpRule to it.
/// - selector: example.v1.Messaging.GetMessage
/// get: /v1/messages/{message_id}/{sub.subfield}
///
/// ## Special notes
///
/// When gRPC Transcoding is used to map a gRPC to JSON REST endpoints, the
/// proto to JSON conversion must follow the [proto3
/// specification](<https://developers.google.com/protocol-buffers/docs/proto3#json>).
///
/// While the single segment variable follows the semantics of
/// [RFC 6570](<https://tools.ietf.org/html/rfc6570>) Section 3.2.2 Simple String
/// Expansion, the multi segment variable **does not** follow RFC 6570 Section
/// 3.2.3 Reserved Expansion. The reason is that the Reserved Expansion
/// does not expand special characters like `?` and `#`, which would lead
/// to invalid URLs. As the result, gRPC Transcoding uses a custom encoding
/// for multi segment variables.
///
/// The path variables **must not** refer to any repeated or mapped field,
/// because client libraries are not capable of handling such variable expansion.
///
/// The path variables **must not** capture the leading "/" character. The reason
/// is that the most common use case "{var}" does not capture the leading "/"
/// character. For consistency, all path variables must share the same behavior.
///
/// Repeated message fields must not be mapped to URL query parameters, because
/// no client library can support such complicated mapping.
///
/// If an API needs to use a JSON array for request or response body, it can map
/// the request or response body to a repeated field. However, some gRPC
/// Transcoding implementations may not support this feature.
/// Nested message and enum types in `HttpRule`.
/// A custom pattern is used for defining custom HTTP verb.
/// The launch stage as defined by [Google Cloud Platform
/// Launch Stages](<https://cloud.google.com/terms/launch-stages>).
/// Required information for every language.
/// Details about how and where to publish client libraries.
/// This message configures the settings for publishing [Google Cloud Client
/// libraries](<https://cloud.google.com/apis/docs/cloud-client-libraries>)
/// generated from the service config.
/// Settings for Java client libraries.
/// Settings for C++ client libraries.
/// Settings for Php client libraries.
/// Settings for Python client libraries.
/// Settings for Node client libraries.
/// Settings for Dotnet client libraries.
/// Settings for Ruby client libraries.
/// Settings for Go client libraries.
/// Describes the generator configuration for a method.
/// Nested message and enum types in `MethodSettings`.
/// The organization for which the client libraries are being published.
/// Affects the url where generated docs are published, etc.
/// To where should client libraries be published?
/// An indicator of the behavior of a given field (for example, that a field
/// is required in requests, or given as output but ignored as input).
/// This **does not** change the behavior in protocol buffers itself; it only
/// denotes the behavior and may affect how API tooling handles the field.
///
/// Note: This enum **may** receive new values in the future.
/// A simple descriptor of a resource type.
///
/// ResourceDescriptor annotates a resource message (either by means of a
/// protobuf annotation or use in the service config), and associates the
/// resource's schema, the resource type, and the pattern of the resource name.
///
/// Example:
///
/// message Topic {
/// // Indicates this message defines a resource schema.
/// // Declares the resource type in the format of {service}/{kind}.
/// // For Kubernetes resources, the format is {api group}/{kind}.
/// option (google.api.resource) = {
/// type: "pubsub.googleapis.com/Topic"
/// pattern: "projects/{project}/topics/{topic}"
/// };
/// }
///
/// The ResourceDescriptor Yaml config will look like:
///
/// resources:
/// - type: "pubsub.googleapis.com/Topic"
/// pattern: "projects/{project}/topics/{topic}"
///
/// Sometimes, resources have multiple patterns, typically because they can
/// live under multiple parents.
///
/// Example:
///
/// message LogEntry {
/// option (google.api.resource) = {
/// type: "logging.googleapis.com/LogEntry"
/// pattern: "projects/{project}/logs/{log}"
/// pattern: "folders/{folder}/logs/{log}"
/// pattern: "organizations/{organization}/logs/{log}"
/// pattern: "billingAccounts/{billing_account}/logs/{log}"
/// };
/// }
///
/// The ResourceDescriptor Yaml config will look like:
///
/// resources:
/// - type: 'logging.googleapis.com/LogEntry'
/// pattern: "projects/{project}/logs/{log}"
/// pattern: "folders/{folder}/logs/{log}"
/// pattern: "organizations/{organization}/logs/{log}"
/// pattern: "billingAccounts/{billing_account}/logs/{log}"
/// Nested message and enum types in `ResourceDescriptor`.
/// Defines a proto annotation that describes a string field that refers to
/// an API resource.
/// Specifies the routing information that should be sent along with the request
/// in the form of routing header.
/// **NOTE:** All service configuration rules follow the "last one wins" order.
///
/// The examples below will apply to an RPC which has the following request type:
///
/// Message Definition:
///
/// message Request {
/// // The name of the Table
/// // Values can be of the following formats:
/// // - `projects/<project>/tables/<table>`
/// // - `projects/<project>/instances/<instance>/tables/<table>`
/// // - `region/<region>/zones/<zone>/tables/<table>`
/// string table_name = 1;
///
/// // This value specifies routing for replication.
/// // It can be in the following formats:
/// // - `profiles/<profile_id>`
/// // - a legacy `profile_id` that can be any string
/// string app_profile_id = 2;
/// }
///
/// Example message:
///
/// {
/// table_name: projects/proj_foo/instances/instance_bar/table/table_baz,
/// app_profile_id: profiles/prof_qux
/// }
///
/// The routing header consists of one or multiple key-value pairs. Every key
/// and value must be percent-encoded, and joined together in the format of
/// `key1=value1&key2=value2`.
/// In the examples below I am skipping the percent-encoding for readablity.
///
/// Example 1
///
/// Extracting a field from the request to put into the routing header
/// unchanged, with the key equal to the field name.
///
/// annotation:
///
/// option (google.api.routing) = {
/// // Take the `app_profile_id`.
/// routing_parameters {
/// field: "app_profile_id"
/// }
/// };
///
/// result:
///
/// x-goog-request-params: app_profile_id=profiles/prof_qux
///
/// Example 2
///
/// Extracting a field from the request to put into the routing header
/// unchanged, with the key different from the field name.
///
/// annotation:
///
/// option (google.api.routing) = {
/// // Take the `app_profile_id`, but name it `routing_id` in the header.
/// routing_parameters {
/// field: "app_profile_id"
/// path_template: "{routing_id=**}"
/// }
/// };
///
/// result:
///
/// x-goog-request-params: routing_id=profiles/prof_qux
///
/// Example 3
///
/// Extracting a field from the request to put into the routing
/// header, while matching a path template syntax on the field's value.
///
/// NB: it is more useful to send nothing than to send garbage for the purpose
/// of dynamic routing, since garbage pollutes cache. Thus the matching.
///
/// Sub-example 3a
///
/// The field matches the template.
///
/// annotation:
///
/// option (google.api.routing) = {
/// // Take the `table_name`, if it's well-formed (with project-based
/// // syntax).
/// routing_parameters {
/// field: "table_name"
/// path_template: "{table_name=projects/*/instances/*/**}"
/// }
/// };
///
/// result:
///
/// x-goog-request-params:
/// table_name=projects/proj_foo/instances/instance_bar/table/table_baz
///
/// Sub-example 3b
///
/// The field does not match the template.
///
/// annotation:
///
/// option (google.api.routing) = {
/// // Take the `table_name`, if it's well-formed (with region-based
/// // syntax).
/// routing_parameters {
/// field: "table_name"
/// path_template: "{table_name=regions/*/zones/*/**}"
/// }
/// };
///
/// result:
///
/// <no routing header will be sent>
///
/// Sub-example 3c
///
/// Multiple alternative conflictingly named path templates are
/// specified. The one that matches is used to construct the header.
///
/// annotation:
///
/// option (google.api.routing) = {
/// // Take the `table_name`, if it's well-formed, whether
/// // using the region- or projects-based syntax.
///
/// routing_parameters {
/// field: "table_name"
/// path_template: "{table_name=regions/*/zones/*/**}"
/// }
/// routing_parameters {
/// field: "table_name"
/// path_template: "{table_name=projects/*/instances/*/**}"
/// }
/// };
///
/// result:
///
/// x-goog-request-params:
/// table_name=projects/proj_foo/instances/instance_bar/table/table_baz
///
/// Example 4
///
/// Extracting a single routing header key-value pair by matching a
/// template syntax on (a part of) a single request field.
///
/// annotation:
///
/// option (google.api.routing) = {
/// // Take just the project id from the `table_name` field.
/// routing_parameters {
/// field: "table_name"
/// path_template: "{routing_id=projects/*}/**"
/// }
/// };
///
/// result:
///
/// x-goog-request-params: routing_id=projects/proj_foo
///
/// Example 5
///
/// Extracting a single routing header key-value pair by matching
/// several conflictingly named path templates on (parts of) a single request
/// field. The last template to match "wins" the conflict.
///
/// annotation:
///
/// option (google.api.routing) = {
/// // If the `table_name` does not have instances information,
/// // take just the project id for routing.
/// // Otherwise take project + instance.
///
/// routing_parameters {
/// field: "table_name"
/// path_template: "{routing_id=projects/*}/**"
/// }
/// routing_parameters {
/// field: "table_name"
/// path_template: "{routing_id=projects/*/instances/*}/**"
/// }
/// };
///
/// result:
///
/// x-goog-request-params:
/// routing_id=projects/proj_foo/instances/instance_bar
///
/// Example 6
///
/// Extracting multiple routing header key-value pairs by matching
/// several non-conflicting path templates on (parts of) a single request field.
///
/// Sub-example 6a
///
/// Make the templates strict, so that if the `table_name` does not
/// have an instance information, nothing is sent.
///
/// annotation:
///
/// option (google.api.routing) = {
/// // The routing code needs two keys instead of one composite
/// // but works only for the tables with the "project-instance" name
/// // syntax.
///
/// routing_parameters {
/// field: "table_name"
/// path_template: "{project_id=projects/*}/instances/*/**"
/// }
/// routing_parameters {
/// field: "table_name"
/// path_template: "projects/*/{instance_id=instances/*}/**"
/// }
/// };
///
/// result:
///
/// x-goog-request-params:
/// project_id=projects/proj_foo&instance_id=instances/instance_bar
///
/// Sub-example 6b
///
/// Make the templates loose, so that if the `table_name` does not
/// have an instance information, just the project id part is sent.
///
/// annotation:
///
/// option (google.api.routing) = {
/// // The routing code wants two keys instead of one composite
/// // but will work with just the `project_id` for tables without
/// // an instance in the `table_name`.
///
/// routing_parameters {
/// field: "table_name"
/// path_template: "{project_id=projects/*}/**"
/// }
/// routing_parameters {
/// field: "table_name"
/// path_template: "projects/*/{instance_id=instances/*}/**"
/// }
/// };
///
/// result (is the same as 6a for our example message because it has the instance
/// information):
///
/// x-goog-request-params:
/// project_id=projects/proj_foo&instance_id=instances/instance_bar
///
/// Example 7
///
/// Extracting multiple routing header key-value pairs by matching
/// several path templates on multiple request fields.
///
/// NB: note that here there is no way to specify sending nothing if one of the
/// fields does not match its template. E.g. if the `table_name` is in the wrong
/// format, the `project_id` will not be sent, but the `routing_id` will be.
/// The backend routing code has to be aware of that and be prepared to not
/// receive a full complement of keys if it expects multiple.
///
/// annotation:
///
/// option (google.api.routing) = {
/// // The routing needs both `project_id` and `routing_id`
/// // (from the `app_profile_id` field) for routing.
///
/// routing_parameters {
/// field: "table_name"
/// path_template: "{project_id=projects/*}/**"
/// }
/// routing_parameters {
/// field: "app_profile_id"
/// path_template: "{routing_id=**}"
/// }
/// };
///
/// result:
///
/// x-goog-request-params:
/// project_id=projects/proj_foo&routing_id=profiles/prof_qux
///
/// Example 8
///
/// Extracting a single routing header key-value pair by matching
/// several conflictingly named path templates on several request fields. The
/// last template to match "wins" the conflict.
///
/// annotation:
///
/// option (google.api.routing) = {
/// // The `routing_id` can be a project id or a region id depending on
/// // the table name format, but only if the `app_profile_id` is not set.
/// // If `app_profile_id` is set it should be used instead.
///
/// routing_parameters {
/// field: "table_name"
/// path_template: "{routing_id=projects/*}/**"
/// }
/// routing_parameters {
/// field: "table_name"
/// path_template: "{routing_id=regions/*}/**"
/// }
/// routing_parameters {
/// field: "app_profile_id"
/// path_template: "{routing_id=**}"
/// }
/// };
///
/// result:
///
/// x-goog-request-params: routing_id=profiles/prof_qux
///
/// Example 9
///
/// Bringing it all together.
///
/// annotation:
///
/// option (google.api.routing) = {
/// // For routing both `table_location` and a `routing_id` are needed.
/// //
/// // table_location can be either an instance id or a region+zone id.
/// //
/// // For `routing_id`, take the value of `app_profile_id`
/// // - If it's in the format `profiles/<profile_id>`, send
/// // just the `<profile_id>` part.
/// // - If it's any other literal, send it as is.
/// // If the `app_profile_id` is empty, and the `table_name` starts with
/// // the project_id, send that instead.
///
/// routing_parameters {
/// field: "table_name"
/// path_template: "projects/*/{table_location=instances/*}/tables/*"
/// }
/// routing_parameters {
/// field: "table_name"
/// path_template: "{table_location=regions/*/zones/*}/tables/*"
/// }
/// routing_parameters {
/// field: "table_name"
/// path_template: "{routing_id=projects/*}/**"
/// }
/// routing_parameters {
/// field: "app_profile_id"
/// path_template: "{routing_id=**}"
/// }
/// routing_parameters {
/// field: "app_profile_id"
/// path_template: "profiles/{routing_id=*}"
/// }
/// };
///
/// result:
///
/// x-goog-request-params:
/// table_location=instances/instance_bar&routing_id=prof_qux
/// A projection from an input message to the GRPC or REST header.