# API style guidelines

Generally follow guidance at https://cloud.google.com/apis/design/, in
particular for proto3 as described at:

* https://cloud.google.com/apis/design/proto3
* https://cloud.google.com/apis/design/naming_convention
* https://developers.google.com/protocol-buffers/docs/style

In addition, the following conventions should be followed:

* The data plane APIs are primarily intended for machine generation and consumption.
  It is expected that the management server is responsible for mapping higher
  level configuration concepts to concrete API concepts. Similarly, static configuration
  fragments may be generated by tools and UIs, etc. The APIs and tools used
  to generate xDS configuration are beyond the scope of the definitions in this
  repository.

* Use [wrapped scalar
  types](https://github.com/google/protobuf/blob/master/src/google/protobuf/wrappers.proto)
  where there is a real need for the field to have a default value that does not
  match the proto3 default (0/false/""). This should not be done for fields
  where the proto3 defaults make sense. All things being equal, pick appropriate
  logic, e.g. enable vs. disable for a `bool` field, such that the proto3
  defaults work, but only where this doesn't result in API gymnastics.

* Always use plural field names for `repeated` fields.

* Prefer `oneof` selections to boolean overloads of fields, for example, prefer:

  ```proto
  oneof path_secifier {
    string simple_path = 1;
    string regex_path = 2;
  }
  ```

  to

  ```proto
  string path = 1;
  bool path_is_regex = 2;
  ```

  This is more efficient, extendable and self-describing.