Execution Context

Guards, interceptors and (through ArgumentsHost) exception filters all receive an object describing what is being executed right now. In a guard or interceptor that is an ExecutionContext:

from austial import CanActivate, ExecutionContext
 
 
class RolesGuard(CanActivate):
    async def can_activate(self, context: ExecutionContext) -> bool:
        request = context.get_request()
        handler = context.get_handler()          # the controller method that will run
        controller = context.get_class()         # the controller class
        ...

Method	Returns
`get_type()`	The kind of request: always `"http"`. Austial has no WebSocket or RPC transport, so the other values NestJS reports (`"ws"`, `"rpc"`) never occur.
`get_request()`	The Starlette `Request`.
`get_response()`	The `Response` being built for this request. Headers you set on it are sent, which is how a guard or interceptor adds a header without owning the handler. `None` when a filter builds its own response.
`get_args()`	`[request, response]`, like Nest’s `[req, res, next]` (there is no `next`).
`get_arg_by_index(i)`	One of those.
`get_class()` / `get_handler()`	The controller class and the handler method, for reading metadata with the `Reflector`.
`switch_to_http()`	The same context (it already is the HTTP one), so code written for NestJS ports over unchanged.
`switch_to_ws()` / `switch_to_rpc()`	Raise `NotImplementedError`: there is no such context to switch to.

Setting a header from a guard or interceptor#

class RequestIdInterceptor(NestInterceptor):
    async def intercept(self, context: ExecutionContext, next: CallHandler):
        context.get_response().headers["X-Request-Id"] = str(uuid4())
        return await next.handle()

Reading handler metadata#

get_handler() and get_class() are what a guard passes to the Reflector to find a custom decorator’s value on the method, falling back to the controller:

required = self.reflector.get_all_and_override(ROLES_KEY, [context.get_handler(), context.get_class()])

In exception filters: `ArgumentsHost`#

A filter’s catch(exception, host) gets an ArgumentsHost, the smaller sibling of ExecutionContext: get_type(), get_request(), get_args() and switch_to_http(). There is no get_response() there: a filter returns the response it wants to send. See Exception Filters.