Api is a light-weight descriptor for an API Interface.

Interfaces are also described as "protocol buffer services" in some contexts, such as by the "service" keyword in a .proto file, but they are different from API Services, which represent a concrete implementation of an interface as opposed to simply a description of methods and bindings. They are also sometimes simply referred to as "APIs" in other contexts, such as the name of this message itself. See https://cloud.google.com/apis/design/glossary for detailed terminology.

Method represents a method of an API interface.

Declares an API Interface to be included in this interface. The including interface must redeclare all the methods from the included interface, but documentation and options are inherited as follows:

• If after comment and whitespace stripping, the documentation string of the redeclared method is empty, it will be inherited from the original method.

• Each annotation belonging to the service config (http, visibility) which is not set in the redeclared method will be inherited.

• If an http annotation is inherited, the path pattern will be modified as follows. Any version prefix will be replaced by the version of the including interface plus the root path if specified.

Example of a simple mixin:

 package google.acl.v1;
 service AccessControl {

Get the underlying ACL object.

   rpc GetAcl(GetAclRequest) returns (Acl) {
     option (google.api.http).get = "/v1/{resource=**}:getAcl";
   }
 }

 package google.storage.v2;
 service Storage {
   rpc GetAcl(GetAclRequest) returns (Acl);

Get a data record.

   rpc GetData(GetDataRequest) returns (Data) {
     option (google.api.http).get = "/v2/{resource=**}";
   }
 }

Example of a mixin configuration:

 apis:
 - name: google.storage.v2.Storage
   mixins:
   - name: google.acl.v1.AccessControl

The mixin construct implies that all methods in AccessControl are also declared with same name and request/response types in Storage. A documentation generator or annotation processor will see the effective Storage.GetAcl method after inheriting documentation and annotations as follows:

 service Storage {

Get the underlying ACL object.

   rpc GetAcl(GetAclRequest) returns (Acl) {
     option (google.api.http).get = "/v2/{resource=**}:getAcl";
   }
   ...
 }

Note how the version in the path pattern changed from v1 to v2.

If the root field in the mixin is specified, it should be a relative path under which inherited HTTP paths are placed. Example:

 apis:
 - name: google.storage.v2.Storage
   mixins:
   - name: google.acl.v1.AccessControl
     root: acls

This implies the following inherited HTTP annotation:

 service Storage {

Get the underlying ACL object.

   rpc GetAcl(GetAclRequest) returns (Acl) {
     option (google.api.http).get = "/v2/acls/{resource=**}:getAcl";
   }
   ...
 }