Common Design Patterns for Symbian OS: The Foundations of Smartphone Software

7.4. Cradle

Intent

Host DLL plug-ins in separate processes, operating at different levels of trust to your own, to securely increase the flexibility of your architecture whilst maintaining communication with each plug-in.

AKA

None known

7.4.1. Problem

7.4.1.1. Context

You need to provide a secure extension point in your component that supports extensive communication between the framework and the plug-ins whilst not overly restricting the plug-in providers.

7.4.1.2. Summary

• Architectural extensibility has to be provided.

• The potential damage caused by plug-ins needs to be limited by minimizing the capabilities they execute with (principle of least privilege).

• It's desirable that the restrictions on who can provide plug-ins are as light as possible.

• You wish to allow plug-ins to operate with a different set of capabilities than the framework.

• You need to support a full communication channel between the framework and the plug-ins after the plug-ins have been loaded.

7.4.1.3. Description

If you're reading this pattern then you've probably tried to get Buckle (see page 252) to work but found that it doesn't provide a solution to this problem since you need to allow the plug-ins to operate at a different level of trust to the framework.

Quarantine (see page 260) is an alternative that does allow plug-ins to operate at a different level of trust to the framework but it only directly supports very simple, one-shot communication between the framework and each plug-in; in this context, ...