types
Operation
Operation is annotation for rpc that returns longrunning operation, describes message types that will be returned in metadata google.protobuf.Any, and in response google.protobuf.Any (for successful operation).
metadata
: string
Optional. If present, rpc returns operation which metadata field will contains message of specified type.
response
: string
Required. rpc returns operation, in case of success response will contains message of specified field.