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# API style guidelines
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Generally follow guidance at https://cloud.google.com/apis/design/, in
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particular for proto3 as described at:
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* https://cloud.google.com/apis/design/proto3
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* https://cloud.google.com/apis/design/naming_convention
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* https://developers.google.com/protocol-buffers/docs/style
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In addition, the following conventions should be followed:
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* For protos that are [frozen](https://www.envoyproxy.io/docs/envoy/latest/configuration/overview/v2_overview#status),
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the following guidelines are followed:
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* Fields should not be renumbered or have their types changed. This is standard proto development
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procedure.
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* Fields should not be **renamed**. This is stricter than standard proto development procedure
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in the sense that it does not break binary wire format. However, it **does** break loading
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of YAML/JSON into protos as well as text protos. Since we consider YAML/JSON to be first class
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inputs, we must not change field names.
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* If fields are deleted, the following syntax should be put in their place:
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```proto
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reserved <field index>;
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```
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E.g.,
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```proto
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reserved 15;
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```
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* The data plane APIs are primarily intended for machine generation and consumption.
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It is expected that the management server is responsible for mapping higher
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level configuration concepts to concrete API concepts. Similarly, static configuration
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fragments may be generated by tools and UIs, etc. The APIs and tools used
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to generate xDS configuration are beyond the scope of the definitions in this
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repository.
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* Use [wrapped scalar
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types](https://github.com/google/protobuf/blob/master/src/google/protobuf/wrappers.proto)
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where there is a real need for the field to have a default value that does not
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match the proto3 defaults (0/false/""). This should not be done for fields
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where the proto3 defaults make sense. All things being equal, pick appropriate
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logic, e.g. enable vs. disable for a `bool` field, such that the proto3
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defaults work, but only where this doesn't result in API gymnastics.
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* Always use plural field names for `repeated` fields, such as `filters`.
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* Always use upper camel case names for message types and enum types without embedded
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acronyms, such as `HttpRequest`.
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* Prefer `oneof` selections to boolean overloads of fields, for example, prefer:
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```proto
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oneof path_secifier {
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string simple_path = 1;
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string regex_path = 2;
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}
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```
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to
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```proto
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string path = 1;
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bool path_is_regex = 2;
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```
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This is more efficient, extendable and self-describing.
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* To represent percentage values, use the Percent message type defined in [api/base.proto](api/base.proto).
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