Alternate AIP-193 recommendation

aip/general/0193/aip.md

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+# Errors
+
+Error handling is an important part of designing simple and intuitive APIs.
+Consistent error handling allows developers to know how to expect to receive
+errors, and to reduce boilerplate by having common error-handling logic, rather
+than being expected to constantly add verbose error handling everywhere.
+
+## Guidance
+
+Services **must** clearly distinguish successful responses from error responses
+by using appropriate HTTP codes:
+- Informational responses **must** use HTTP status codes between 100 and 199.
+- Successful responses **must** use HTTP status codes between 200 and 399.
+- Errors indicating a problem with the user's request **must** use HTTP status
+  codes between 400 and 499.
+- Errors indicating a problem with the server's handling of an valid request
+  **must** use HTTP status codes between 500 and 599.
+
+### Structure
+
+Error responses **should** conform to the following interface:
+
+```typescript
+interface Error {
+  //A machine-readable code indicating the type of error (like `name_too_long`). This value is parseable for programmatic error handling.
+  code: string;
+
+  //A human readable description of the problem. Should not change from occurrence to occurrence (except for localization).
+  title?: string
+
+  //The HTTP status code between 100 and 500
+  status?: integer
+
+  //A human-readable explanation specific to this occurrence of the problem
+  detail?: string
+
+  //A unique identifier that identifies the specific occurrence of the problem. Can be provided to the API owner for debugging purposes.
+  id?: string
+}
+```
+
+- The `title` field is intended for consumption by humans, and therefore
+  **may** change, even within a single version.
+- The `code` field is intended to have code written against it, and therefore
+  **must not** change. Values for this field should be 0-63 characters, and use
+  only lower-case letters, numbers, and the `-` character.
+
+
+
+### Messages
+
+Error messages **should** help a reasonably technical user understand and
+resolve the issue, and **should not** assume that the user is an expert in the
+particular API. Additionally, error messages **must not** assume that the user
+will know anything about its underlying implementation.
+
+Error messages **should** be brief but actionable. Any extra information
+**should** be provided in a `details` field. If even more information is
+necessary, the service **should** provide a link where a reader can get more
+information or ask questions to help resolve the issue.
+
+### Localization
+
+Error messages **must** be in American English. If a localized error message is
+also required, the service **should** provide the following structure within
+its `details`:
+
+```typescript
+interface LocalizedMessage {
+  // The locale for this error message.
+  // Follows the spec defined at http://www.rfc-editor.org/rfc/bcp/bcp47.txt.
+  // Examples: 'en-US', 'de-CH', 'es-MX'
+  locale: string;
+
+  // The localized error message in the above locale.
+  message: string;
+}
+```
+
+### Partial errors
+
+APIs **should not** support partial errors. Partial errors add significant
+complexity for users, because they usually sidestep the use of error codes, or
+move those error codes into the response message, where the user must write
+specialized error handling logic to address the problem.
+
+However, occasionally partial errors are unavoidable, particularly in bulk
+operations where it would be hostile to users to fail an entire large request
+because of a problem with a single entry.
+
+Methods that require partial errors **should** use long-running operations (as
+described in AIP-151), and the method **should** put partial failure
+information in the metadata message. The errors themselves **must** still be
+represented with an error object.
+
+## Further reading
+
+- For which error codes to retry, see AIP-194.
+
+## Changelog
+
+- **2020-09-02**: Refactored errors AIP to be more generic.
+- **2020-01-22**: Added a reference to the `ErrorInfo` message in gRPC.
+- **2019-10-14**: Added guidance restricting error message mutability to if
+  there is a machine-readable identifier present.
+- **2019-09-23**: Added guidance about error message strings being able to
+  change.

aip/general/0193/aip.yaml

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+---
+id: 193
+state: approved
+created: 2019-07-26
+placement:
+  category: polish
+  order: 30