Horizon Exceptions

Exceptions raised by the Horizon code and the machinery for handling them.

exception horizon.exceptions.AlreadyExists(name, resource_type)

Exception to be raised when trying to create an API resource which already exists.

exception horizon.exceptions.Conflict

Generic error to replace all “Conflict”-type API errors.

exception horizon.exceptions.HandledException(wrapped)

Used internally to track exceptions that have gone through horizon.exceptions.handle() more than once.

exception horizon.exceptions.HorizonException

Base exception class for distinguishing our own exception classes.

class horizon.exceptions.HorizonReporterFilter

Error report filter that’s always active, even in DEBUG mode.

get_traceback_frame_variables(request, tb_frame)

Replaces the values of variables marked as sensitive with stars (*****).

exception horizon.exceptions.Http302(location, message=None)

Error class which can be raised from within a handler to cause an early bailout and redirect at the middleware level.

exception horizon.exceptions.NotAuthenticated

Raised when a user is trying to make requests and they are not logged in.

The included HorizonMiddleware catches NotAuthenticated and handles it gracefully by displaying an error message and redirecting the user to a login page.

exception horizon.exceptions.NotAuthorized

Raised whenever a user attempts to access a resource which they do not have permission-based access to (such as when failing the require_perms() decorator).

The included HorizonMiddleware catches NotAuthorized and handles it gracefully by displaying an error message and redirecting the user to a login page.

exception horizon.exceptions.NotFound

Generic error to replace all “Not Found”-type API errors.

exception horizon.exceptions.RecoverableError

Generic error to replace any “Recoverable”-type API errors.

exception horizon.exceptions.ServiceCatalogException(service_name)

Raised when a requested service is not available in the ServiceCatalog returned by Keystone.

exception horizon.exceptions.WorkflowError

Exception to be raised when something goes wrong in a workflow.

exception horizon.exceptions.WorkflowValidationError

Exception raised during workflow validation if required data is missing, or existing data is not valid.

horizon.exceptions.check_message(keywords, message)

Checks an exception for given keywords and raises a new ActionError with the desired message if the keywords are found. This allows selective control over API error messages.

horizon.exceptions.handle(request, message=None, redirect=None, ignore=False, escalate=False, log_level=None, force_log=None)

Centralized error handling for Horizon.

Because Horizon consumes so many different APIs with completely different Exception types, it’s necessary to have a centralized place for handling exceptions which may be raised.

Exceptions are roughly divided into 3 types:

1. UNAUTHORIZED: Errors resulting from authentication or authorization problems. These result in being logged out and sent to the login screen.
2. NOT_FOUND: Errors resulting from objects which could not be located via the API. These generally result in a user-facing error message, but are otherwise returned to the normal code flow. Optionally a redirect value may be passed to the error handler so users are returned to a different view than the one requested in addition to the error message.
3. RECOVERABLE: Generic API errors which generate a user-facing message but drop directly back to the regular code flow.

All other exceptions bubble the stack as normal unless the ignore argument is passed in as True, in which case only unrecognized errors are bubbled.

If the exception is not re-raised, an appropriate wrapper exception class indicating the type of exception that was encountered will be returned.