Enabling API Virtualization on Android for Platform Openness

This morning I was at Taeyeon Ki's dissertation proposal. He presented his work on enabling openness (hackability/tinkerability) in Android platform-side.

He defined openness as being able to participate in innovation and distribution, and gave SDN and FUSE are examples of openness.

He argued that mobile vendors control their platforms tightly, and this prevents tinkering the platform and obstructs innovation. Even though you can innovate at the app side, the OS/platform side is closed for tinkering. He posed the question: how can we enable anyone to easily develop distribute new platform-level functionality?

To answer this question, he presented his work in two projects: Reptor and Mimic.


Reptor is a bytecode instrumentation tool enabling api virtualization on Android. Reptor does this by intercepting calls and redirecting them to a new implementation of the method called.

Intersecting calls to methods is not straightforward. Doing just method name substitution cannot handle calls to class level features: class hierarchy, interface, abstract class, etc. So instead of replacing the method, the Reptor tool replaces entire class. Class level replacement approach works well with callbacks in Android as it ensures that typecasting is correctly handled.

One use case for Reptor is to change some platform-level components used in an app with a more suitable one depending on the region. China and Korea do not have Google Play store, they run their own app-stores for Android. So in China and Korea Google Maps (which is an integral component of Play Store) is not available. Apps there use a downgraded static web map mostly. But with Reptor, it is possible to wrap those applications and redirect the maps calls to Amazon map. Taeyeon showed a demo of this on the Airbnb app.

Reptor has been dummy-tested with 1200 popular apps from Google Play. It has been tested for 32 benchmarked apps with more in depth tests, where runtime checks performed. For this in-depth tests for showing runtime equivalence the Mimic tool described below has been used. The tests showed that Reptor achieves minimal overhead in memory, and performance.

While run-time testing via Mimic is helpful for checking if Reptor substitution at the application of one platform-component with another is "correct" with respect to the platform-level classes, better definition of "correctness" and better framing/formalization of the problem will help this work.


Mimic is an automated UI behavior comparison testing system that provides runtime behavioral compatibility check between original and instrumented app. (I think this is under submission or to appear state.)

When I heard this description, I combined this and Reptor together in my mind, and all I could think of was that the combination can be great for automating click farms for smartphone apps!

Taeyeon had something more useful and honest in mind. There are a dozen different android versions in use. A typical app posts several updates a month and the  developers struggle to test their apps with all these different environments. Mimic combined with Reptor can help perform these tests in an automated way? (Well, still sounds a lot like click farm to me :-)

Taeyon explained their follow-the-leader testing model, where Mimic replicates the user behavior at the leader to the followers.


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