Automatically populate request_id-like fields to make requests idempotent

[coryan]

Some services have fields that (when populated with unique values) make the requests idempotent. An example is service control with fields like this:

  // Optional. A unique identifier for this request. UUID is the recommended
  // format, but other formats are still accepted. This request is only
  // idempotent if a `request_id` is provided.
  string request_id = 5 [
    (google.api.field_info).format = UUID4,
    (google.api.field_behavior) = OPTIONAL
  ];

https://github.com/googleapis/googleapis/blob/7d73737e0e826ac683a4b5b19352feabf51bbc57/google/storage/control/v2/storage_control.proto#L202-L208

The field does not need to be called request_id. The name of the field comes from the service config YAML file, for example:

publishing:
  method_settings:
  - selector: google.storage.control.v2.StorageControl.CreateFolder
    auto_populated_fields:
    - request_id

https://github.com/googleapis/googleapis/blob/65b63cc4440e642d95a0c9562233f9ef2511c787/google/storage/control/v2/storage_v2.yaml#L44-L48

The full set of conditions is then:

• The field must appear in the YAML file.
• The field is a non-repeated string.
• The field has the google.api.field_info annotation
• The field format is UUID4

See Also

go/client-populate-request-id-prd
go/client-populate-request-id-design