protoc-gen-openapi (#221)

* First steps toward a protoc plugin for generating OpenAPI models.

Based on the Go code generation plugin (protoc-gen-go) and the
gnostic petstore-builder sample app.

* protoc-gen-openapi operation stubs

* updated, fixed build problems

* preliminary structural improvements to put everything in a single spec.

* handle more field and array types + patch requests

* work-in-progress, focusing on generating OpenAPI v3 from protoc-gen-openapi

* protoc-gen-openapi only generates v3, now includes parameters

* protoc-gen-openapi: get API name and description from protos.

* protoc-gen-openapi: only export schemas that are used

* protoc-gen-openapi: include message and field comments in openapi

* protoc-gen-openapi: mark output-only fields

* protoc-gen-openapi: general cleanup

* protoc-gen-openapi: add test

* protoc-gen-openapi: update to use the v2 protobuf-go plugin API

* protoc-gen-openapi: remove unneeded parameters from buildOperationV3

* protoc-gen-openapi: remove blank lines

apps/protoc-gen-openapi/README.md

@@ -0,0 +1,20 @@
+# protoc-gen-openapi
+
+This directory contains a protoc plugin that generates an
+OpenAPI description for a REST API that corresponds to a
+Protocol Buffer service.
+
+Installation:
+
+        go get github.com/googleapis/gnostic
+        go install github.com/googleapis/gnostic/apps/protoc-gen-openapi
+
+
+Usage:
+
+	protoc sample.proto -I. --openapi_out=.
+
+This runs the plugin for a file named `sample.proto` which 
+refers to additional .proto files in the same directory as
+`sample.proto`. Output is written to the current directory.
+

apps/protoc-gen-openapi/examples/google/api/annotations.proto

@@ -0,0 +1,31 @@
+// Copyright (c) 2015, Google Inc.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+syntax = "proto3";
+
+package google.api;
+
+import "google/api/http.proto";
+import "google/protobuf/descriptor.proto";
+
+option go_package = "google.golang.org/genproto/googleapis/api/annotations;annotations";
+option java_multiple_files = true;
+option java_outer_classname = "AnnotationsProto";
+option java_package = "com.google.api";
+option objc_class_prefix = "GAPI";
+
+extend google.protobuf.MethodOptions {
+  // See `HttpRule`.
+  HttpRule http = 72295728;
+}

apps/protoc-gen-openapi/examples/google/api/client.proto

@@ -0,0 +1,101 @@
+// Copyright 2019 Google LLC.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+syntax = "proto3";
+
+package google.api;
+
+import "google/protobuf/descriptor.proto";
+
+option go_package = "google.golang.org/genproto/googleapis/api/annotations;annotations";
+option java_multiple_files = true;
+option java_outer_classname = "ClientProto";
+option java_package = "com.google.api";
+option objc_class_prefix = "GAPI";
+
+
+extend google.protobuf.ServiceOptions {
+  // The hostname for this service.
+  // This should be specified with no prefix or protocol.
+  //
+  // Example:
+  //
+  //   service Foo {
+  //     option (google.api.default_host) = "foo.googleapi.com";
+  //     ...
+  //   }
+  string default_host = 1049;
+
+  // OAuth scopes needed for the client.
+  //
+  // Example:
+  //
+  //   service Foo {
+  //     option (google.api.oauth_scopes) = \
+  //       "https://www.googleapis.com/auth/cloud-platform";
+  //     ...
+  //   }
+  //
+  // If there is more than one scope, use a comma-separated string:
+  //
+  // Example:
+  //
+  //   service Foo {
+  //     option (google.api.oauth_scopes) = \
+  //       "https://www.googleapis.com/auth/cloud-platform,"
+  //       "https://www.googleapis.com/auth/monitoring";
+  //     ...
+  //   }
+  string oauth_scopes = 1050;
+}
+
+
+extend google.protobuf.MethodOptions {
+  // A definition of a client library method signature.
+  //
+  // In client libraries, each proto RPC corresponds to one or more methods
+  // which the end user is able to call, and calls the underlying RPC.
+  // Normally, this method receives a single argument (a struct or instance
+  // corresponding to the RPC request object). Defining this field will
+  // add one or more overloads providing flattened or simpler method signatures
+  // in some languages.
+  //
+  // The fields on the method signature are provided as a comma-separated
+  // string.
+  //
+  // For example, the proto RPC and annotation:
+  //
+  //   rpc CreateSubscription(CreateSubscriptionRequest)
+  //       returns (Subscription) {
+  //     option (google.api.method_signature) = "name,topic";
+  //   }
+  //
+  // Would add the following Java overload (in addition to the method accepting
+  // the request object):
+  //
+  //   public final Subscription createSubscription(String name, String topic)
+  //
+  // The following backwards-compatibility guidelines apply:
+  //
+  //   * Adding this annotation to an unannotated method is backwards
+  //     compatible.
+  //   * Adding this annotation to a method which already has existing
+  //     method signature annotations is backwards compatible if and only if
+  //     the new method signature annotation is last in the sequence.
+  //   * Modifying or removing an existing method signature annotation is
+  //     a breaking change.
+  //   * Re-ordering existing method signature annotations is a breaking
+  //     change.
+  repeated string method_signature = 1051;
+}

apps/protoc-gen-openapi/examples/google/api/field_behavior.proto

@@ -0,0 +1,80 @@
+// Copyright 2019 Google LLC.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+syntax = "proto3";
+
+package google.api;
+
+import "google/protobuf/descriptor.proto";
+
+option go_package = "google.golang.org/genproto/googleapis/api/annotations;annotations";
+option java_multiple_files = true;
+option java_outer_classname = "FieldBehaviorProto";
+option java_package = "com.google.api";
+option objc_class_prefix = "GAPI";
+
+
+// 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.
+enum FieldBehavior {
+  // Conventional default for enums. Do not use this.
+  FIELD_BEHAVIOR_UNSPECIFIED = 0;
+
+  // Specifically denotes a field as optional.
+  // While all fields in protocol buffers are optional, this may be specified
+  // for emphasis if appropriate.
+  OPTIONAL = 1;
+
+  // Denotes a field as required.
+  // This indicates that the field **must** be provided as part of the request,
+  // and failure to do so will cause an error (usually `INVALID_ARGUMENT`).
+  REQUIRED = 2;
+
+  // Denotes a field as output only.
+  // This indicates that the field is provided in responses, but including the
+  // field in a request does nothing (the server *must* ignore it and
+  // *must not* throw an error as a result of the field's presence).
+  OUTPUT_ONLY = 3;
+
+  // Denotes a field as input only.
+  // This indicates that the field is provided in requests, and the
+  // corresponding field is not included in output.
+  INPUT_ONLY = 4;
+
+  // Denotes a field as immutable.
+  // This indicates that the field may be set once in a request to create a
+  // resource, but may not be changed thereafter.
+  IMMUTABLE = 5;
+}
+
+
+extend google.protobuf.FieldOptions {
+  // A designation of a specific field behavior (required, output only, etc.)
+  // in protobuf messages.
+  //
+  // Examples:
+  //
+  //   string name = 1 [(google.api.field_behavior) = REQUIRED];
+  //   State state = 1 [(google.api.field_behavior) = OUTPUT_ONLY];
+  //   google.protobuf.Duration ttl = 1
+  //     [(google.api.field_behavior) = INPUT_ONLY];
+  //   google.protobuf.Timestamp expire_time = 1
+  //     [(google.api.field_behavior) = OUTPUT_ONLY,
+  //      (google.api.field_behavior) = IMMUTABLE];
+  repeated FieldBehavior field_behavior = 1052;
+}