Exercise 2: Protection Proxy

Scenario

The dashboard now has user roles. Not every role should be allowed to call every method on the report service.

The access rules are:

Role	get_metadata()	get_content()	delete_report()
viewer	yes	no	no
analyst	yes	yes	no
admin	yes	yes	yes
anything else	no	no	no

Notice that delete_report() is a new method that did not exist in Exercise 1. The subject interface has been extended to include it.

Your task is to add a protection proxy that enforces these rules before forwarding any call.

What you need to implement

Open exercise2.py and implement ProtectedReportProxy.

The proxy must:

• Wrap any ReportService instance and a role string.
• Before forwarding any call, check that the current role is allowed to make that call. Raise PermissionError with a clear message if it is not.
• Implement a single _check(method_name) helper that contains the permission logic. Do not duplicate that logic in each method.
• All three methods must be present and enforced.

The access rules are already defined for you in ALLOWED_METHODS.

The interface

class ReportService(ABC):
    def get_metadata(self) -> ReportMetadata: ...
    def get_content(self) -> str: ...
    def delete_report(self) -> None: ...

Running the tests

pytest exercise2.py -v

Hints

• _check(method_name) should look up the role in ALLOWED_METHODS and raise PermissionError if the method name is not in the allowed set. An unknown role should be treated the same as an empty allowed set.

• Each public method calls _check("method_name") first, then forwards:

def get_content(self) -> str:
    self._check("get_content")
    return self._service.get_content()

• The proxy does not need to know what the methods do. It only needs to know whether the current role is allowed to call them.

What to notice when it works

A viewer can read report titles but cannot download content or delete anything. An analyst can read and download but cannot delete. An admin can do everything. An unknown role is denied everything, including metadata.

The RealReportService itself has no permission-checking code. All access control lives in the proxy.