[littlegrasscao]

Summary

• render every failure as the protocol's {errorCode, message} JSON body through ApiExceptionHandler, an Armeria exception handler and decorator that any Armeria host can register
• ApiFailure maps failures to a status, error code, and message:
  • ApiException keeps its own status and code
  • a missing asset is 404 RESOURCE_DOES_NOT_EXIST; a denied asset is 403 PERMISSION_DENIED; an unsupported asset type is 400 INVALID_PARAMETER_VALUE
  • CatalogAuthenticationException, a caller token the catalog cannot authenticate, is 401 UNAUTHENTICATED, with WWW-Authenticate: Bearer
  • CatalogAuthorizationException, a caller without the requested privilege, is 403 PERMISSION_DENIED
  • other catalog failures are 502 CATALOG_ERROR; unreadable bodies and illegal arguments are 400; uniqueness violations are 409 RESOURCE_ALREADY_EXISTS; anything else is 500 INTERNAL_ERROR
• the local catalog reports a missing or unknown bearer token as CatalogAuthenticationException
• the standalone server answers unknown routes with a 404 in the protocol's error format

Testing

• mvn clean install: 65 tests passed
• ApiFailureTest: every failure mapping, including 401 for catalog authentication failures
• ApiExceptionHandlerTest: Armeria's own failures (unrouted requests, other statuses, unreadable bodies, invalid parameters), the JSON body, WWW-Authenticate on 401, and failures a service throws or its response fails with
• UnknownRouteTest: an unknown route on the standalone server is a 404 with the protocol body
• LocalCatalogConnectorTest: an unknown token is a CatalogAuthenticationException

Stacked on #91.