feat: AIP-151 – Long-running operations

aip/general/0151/aip.md.j2

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+# Long-running requests
+
+Occasionally, a service may need to expose an operation that takes a
+significant amount of time to complete. In these situations, it is often a poor
+user experience to simply block while the task runs; rather, it is better to
+return some kind of promise to the user, and allow the user to check back in
+later.
+
+The long-running request pattern is roughly analogous to a [Future][] in Python
+or Java, or a [Node.js Promise][]. Essentially, the user is given a token that
+can be used to track progress and retrieve the result.
+
+## Guidance
+
+Operations that might take a significant amount of time to complete **should**
+return a `202 Accepted` response along with an identifier that can be used to
+track the status of the request and ultimately retrieve the result.
+
+Any single operation defined in an API surface **must** either _always_ return
+`202 Accepted` along with a request identifier, or _never_ do so. A service
+**must not** return a `200 OK` response with the result if it is "fast enough",
+and `202 Accepted` if it is not fast enough, because such behavior adds
+significant burdens for clients.
+
+**Note:** User expectations can vary on what is considered "a significant
+amount of time" depending on what work is being done. A good rule of thumb is
+10 seconds.
+
+### Status monitor representation
+
+The response to a long-running request **should** be a "status monitor" having
+the following common format:
+
+```typescript
+interface StatusMonitor {
+  // The identifier for this status monitor.
+  id: string;
+
+  // Whether the request is done.
+  done: boolean;
+
+  // The result of the request.
+  // Only populated if the request is done and was successful.
+  response: any;
+
+  // The error that arose from the request.
+  // Only populated if the request is done and was unsuccessful.
+  error: Error;
+
+  // Metadata associated with the request.
+  // Populated throughout the life of the request, including after
+  // it completes.
+  metadata: any;
+}
+```
+
+- If the `done` field is `true`, then one and exactly one of the `response` and
+  `error` fields **must** be populated.
+  - If the `done` field is `false`, then the `response` and `error` fields
+    **must not** be populated.
+- The `response` and `metadata` fields **may** be any type that the service
+  determines to be appropriate, but **must** always be the same type for any
+  particular operation.
+  - The `response` and `metadata` types **should** be defined in the same API
+    surface as the operation itself.
+  - The `response` and `metadata` types that need no data **should** use a
+    custom-defined empty struct rather than a common void or empty type, to
+    permit future extensibility.
+
+### Querying a status monitor
+
+The service **must** provide an endpoint to query the status of the operation,
+which **must** accept the operation identifier and **should not** include other
+parameters:
+
+```http
+GET /v1/statusMonitors/{status_monitor} HTTP/2
+Host: library.googleapis.com
+Accept: application/json
+```
+
+The endpoint **must** return a `StatusMonitor` as described above.
+
+### Standard methods
+
+APIs **may** return an `StatusMonitor` from the [`Create`][aip-133],
+[`Update`][aip-134], or [`Delete`][aip-135] standard methods if appropriate. In
+this case, the `response` field **must** be the standard and expected response
+type for that standard method.
+
+When creating or deleting a resource with a long-running request, the resource
+**should** be included in [`List`][aip-132] and [`Get`][aip-131] calls;
+however, the resource **should** indicate that it is not usable, generally with
+a [state enum][aip-216].
+
+### Parallel requests
+
+A resource **may** accept multiple requests that will work on it in parallel,
+but is not obligated to do so:
+
+- Resources that accept multiple parallel requests **may** place them in a
+  queue rather than work on the requests simultaneously.
+- Resource that does not permit multiple requests in parallel (denying any new
+  request until the one that is in progress finishes) **must** return
+  `409 Conflict` if a user attempts a parallel request, and include an error
+  message explaining the situation.
+
+### Expiration
+
+APIs **may** allow their status monitor resources to expire after sufficient
+time has elapsed after the request completed.
+
+**Note:** A good rule of thumb for status monitor expiry is 30 days.
+
+### Errors
+
+Errors that prevent a long-running request from _starting_ **must** return an
+error response (AIP-193), similar to any other method.
+
+Errors that occur over the course of a request **may** be placed in the
+metadata message. The errors themselves **must** still be represented with a
+canonical error object.
+
+## Interface Definitions
+
+{% tab proto %}
+
+When using protocol buffers, the well-known type `google.longrunning.Operation`
+is used.
+
+**Note:** For historical reasons, Google uses the term `Operation` to represent
+what this document describes as a `StatusMonitor`.
+
+{% sample 'lro.proto', 'rpc WriteBook' %}
+
+- The response type **must** be `google.longrunning.Operation`. The `Operation`
+  proto definition **must not** be copied into individual APIs.
+  - The response **must not** be a streaming response.
+- The method **must** include a `google.longrunning.operation_info` annotation,
+  which **must** define both response and metadata types.
+  - The response and metadata types **must** be defined in the file where the
+    RPC appears, or a file imported by that file.
+  - If the response and metadata types are defined in another package, the
+    fully-qualified message name **must** be used.
+  - The response type **should not** be `google.protobuf.Empty` (except for
+    [`Delete`][aip-135] methods), unless it is certain that response data will
+    _never_ be needed. If response data might be added in the future, define an
+    empty message for the RPC response and use that.
+  - The metadata type is used to provide information such as progress, partial
+    failures, and similar information on each `GetOperation` call. The metadata
+    type **should not** be `google.protobuf.Empty`, unless it is certain that
+    metadata will _never_ be needed. If metadata might be added in the future,
+    define an empty message for the RPC metadata and use that.
+- APIs with messages that return `Operation` **must** implement the
+  [`Operations`][lro] service. Individual APIs **must not** define their own
+  interfaces for long-running operations to avoid inconsistency.
+
+{% tab oas %}
+
+{% sample 'lro.oas.yaml', 'paths' %}
+
+- `202` **must** be the only success status code defined.
+- The `202` response **must** define an `application/json` response body and no other
+  response content types.
+- The response body schema **must** be an object with `name`, `done`, and `result`
+  properties as described above for a StatusMonitor
+- The response body schema **may** contain an object property named `metadata` to
+  hold service-specific metadata associated with the operation, for example progress
+  information and common metadata such as create time.  The service **should** define
+  the contents of the `metadata` object in a separate schema, which **should** specify
+  `additionalProperties: true` to allow for future extensibility.
+- The `response` property **must** be a schema that defines the success
+  response for the operation. For an operation that typically gives a `204 No Content`
+  response, such as a `Delete`, `response` should be defined as an empty object schema.
+  For a standard `Get/Create/Update` operation, `response` should be a representation
+  of the resource.
+- If a service has any long running operations, the service **must** define an
+  `StatusMonitor` resource with a `list` operation to retrieve a potentially filtered
+  list of status monitors and a `get` operation to retrieve a specific status monitor
+  by its `name`.
+
+{% endtabs %}
+
+<!-- prettier-ignore-start -->
+[google.rpc.Status]: https://github.com/googleapis/api-common-protos/blob/master/google/rpc/S.proto
+[lro]: https://github.com/googleapis/api-common-protos/blob/master/google/longrunning/operations.proto
+[node.js promise]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Guide/Using_promises
+[future]: https://docs.python.org/3/library/concurrent.futures.html#concurrent.futures.Future
+<!-- prettier-ignore-end -->

aip/general/0151/aip.yaml

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+---
+id: 151
+state: reviewing
+created: 2019-07-25
+placement:
+  category: operations
+  order: 70

aip/general/0151/lro.oas.yaml

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+openapi: 3.0.3
+info:
+  title: Library
+  version: 1.0.0
+paths:
+  /v1/resources:
+    post:
+      operationId: write_book
+      description: Write a book.
+      responses:
+        202:
+          description: OK
+          content:
+            application/json:
+              schema:
+                $ref: '#/components/schemas/WriteBookStatus'
+
+components:
+  schemas:
+    StatusMonitor:
+      description: The status of a long running operation.
+      properties:
+        name:
+          type: string
+          description: The server-assigned name, which is only unique within the same service that originally returns it.
+        done:
+          type: boolean
+          description: >-
+            If the value is false, it means the operation is still in progress. If true, the operation is completed,
+            and either response or error is available.
+        error:
+          $ref: '#/components/schemas/Error'
+      required:
+        - name
+        - done
+
+    WriteBookStatus:
+      description: The status of a write_book operation.
+      allOf:
+        - $ref: '#/components/schemas/StatusMonitor'
+        - type: object
+          properties:
+            response:
+              type: string
+              description: The text that was written.
+            metadata:
+              type: object
+              properties:
+                start_time:
+                  type: string
+                  format: date-time
+                  description: The time the operation started.
+                progress_percent:
+                  type: integer
+                  format: int32
+                  description: The current progress, expressed as an integer.
+                state:
+                  type: string
+                  description: The current state of the operation.
+                  enum:
+                    - STATE_UNSPECIFIED
+                    - RUNNING
+                    - CANCELLING
+                    - CANCELLED
+                    - FAILED

aip/general/0151/lro.proto

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+// Copyright 2020 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";
+
+import "google/api/annotations.proto";
+import "google/api/resource.proto";
+import "google/longrunning/operations.proto";
+import "google/protobuf/timestamp.proto";
+
+service Library {
+  // Write a book.
+  rpc WriteBook(WriteBookRequest) returns (google.longrunning.Operation) {
+    option (google.api.http) = {
+      post: "/v1/{parent=publishers/*}/books:write"
+      body: "*"
+    };
+    option (google.longrunning.operation_info) = {
+      response_type: "WriteBookResponse"
+      metadata_type: "WriteBookMetadata"
+    };
+  }
+}
+
+// The request message for the WriteBook endpoint.
+// Unlike the response, this message is accepted directly.
+message WriteBookRequest {
+  // The publisher for which the book is to be written.
+  string parent = 1 [(google.api.resource_reference) = {
+    child_type: "library.googleapis.com/Book"
+  }];
+
+  // The title of the new book.
+  string title = 2;
+}
+
+// The response message for the WriteBook endpoint.
+// When WriteBook is called, it will not send this response directly; instead,
+// it sends a long-running operation; the operation will contain this in
+// the `response` field once it completes.
+message WriteBookResponse {
+  // The text that was written.
+  string text = 1;
+}
+
+// The metadata message for the WriteBook endpoint.
+// This is populated in the `metadata` field for all WriteBook LROs.
+message WriteBookMetadata {
+  // The time the operation started.
+  google.protobuf.Timestamp start_time = 1;
+
+  // The current progress, expressed as an integer: [0, 100].
+  int32 progress_percent = 2;
+
+  enum State {
+    STATE_UNSPECIFIED = 0;
+
+    // The operation is running.
+    RUNNING = 1;
+
+    // The operation is still running, but cancellation has been requested
+    // and accepted, and is in progress.
+    CANCELLING = 2;
+
+    // The operation was cancelled.
+    CANCELLED = 3;
+
+    // The operation failed.
+    FAILED = 4;
+  }
+
+  // The current state of the operation.
+  State state = 3;
+}