The ledger API is sending a status and closing the connection on unexpected errors for every interface that extends ledger.ErrorNotifier. These interfaces must also implement a |Sync| method that will return when all requests called before the |Sync| call have been handled.
When impementing such an interface, one must keep track of each connection to be able to close it with the correct status in case of error, and must also implement the |Sync| method.
To reduce the amount of repeating code, the files in this directory allow to automatically generate an ErrorNotifierDelegate and an implementation of the base interface that delegates to it.
When one wants to implement an interface extending ledger.ErrorNotifier, one therefore only need to implement the generated delegate interface. For each method in the initial interface, the delegate will have a corresponding method with an additional callback taking a ::fuchsia::ledger::Status. The implementor must call this additional callback when the call is finished, with either Status::OK if the call is successful, or with any error status if it is not.
When one wants to bind a request, one can instantiate a new ErrorNotifierBinding, associating it with an implementation of the Delegate. The binding will take care of forwarding the call to the Delegate, as well as handling the error reporting and the |Sync| calls.
For an example, see error_notifier_proxy_base_unittest.cc, which implements the ErrorNotifierTestDelegate interface that is automatically generated from the ErrorNotifierTest FIDL interface defined in fidl/error_notifier_test.fidl.
