Apache Web Server Execution Tracing Using Third Eye
Testing of modern software systems that integrate many components developed by different teams is a difficult task. Third Eye is a framework for tracing and validating software systems using application domain events. We use formal descriptions of the constraints between events to identify violations in execution traces. Third Eye is a flexible and modular framework that can be used in different products. We present the validation of the Apache Web Server access policy implementation. The results indicate that our tool is a helpful addition to software development infrastructure. Nowadays, many software-intensive systems such as personal communication devices or communication network elements integrate many dozens of software components that are designed to run on different types of hardware, to interoperate with different environments and to be configurable for different modes of operation and styles of use. The situation is further complicated by a fact that these components are often developed by geographically distributed teams, using different programming languages, development tools and even different design and development methodologies. All this makes complete testing of these systems in a lab very hard. In the Third Eye project [4], we focused on abstract representation of software - its architecture. We have defined a methodology for tracing execution of software by reporting events meaningful in the application domain or essential from the implementation point of view. Many ideas incorporated in the Third Eye framework were inspired by the Logic Assurance system [5] and work on enforcing architectural constraints [2]. In Third Eye, we have used different technologies to make the framework more extensible, to allow its integration with other trace analysis tools and specification languages. The implemented portable prototype of the Third Eye framework includes reusable software components for event definition and reporting and stand-alone tools for storage and query of event traces, constraint specification and trace analysis. 2 THIRD EYE ARCHITECTURE A central decision of Third Eye framework is what information from the execution state of the program is traced. We decided to trace occurrences of events (Figure 1). Events cross the boundary between the application and implementation domains allowing abstract specifications that use event properties and a simple representation in the implementation domain. Such representation helps to produce traces without introducing new errors. “Event” in this case is a qualitative change in the state of an entity either meaningful in the application domain or significant architecturally. In Third Eye framework, events are typed objects. Event type has a name, a list of named and typed properties, and the type constructor. Third Eye event types are similar to classes in programming languages although the only method associated with the event type is its constructor. We allow event type inheritance. To report an event, developers specify the type of the event and set values of the event properties. Developers need to set only the properties that were not set already by the event constructor. Events in Third Eye are characterized by the time and location of their occurrence. Correct behavior specifications define constraints on the properties of the events, their sequence, location, and timing. We use formal descriptions of the constraints between events to identify violations in execution traces.