Xianyu's Online Issue Replay System for Mobile Apps

The article describes a system developed by Xianyu's technical team to reproduce and locate user-side issues after app release by recording UI operations and external data, then replaying them offline.

Background: Traditional user feedback via text/screenshots or video is inefficient; developers struggle to understand and reproduce issues.

Significance: The replay system allows users to simply re‑operate the app to reproduce problems, developers get a script that can be replayed to view the issue exactly as a video, and runtime data (local, network, stack) is available for debugging.

Technical Principle: The system splits into recording and playback. Recording captures UI events and external data (phone internal/external, app internal). Playback drives UI operations and re‑injects recorded data.

Key Technologies: 1) Simulated touch events – capturing touch data in UIApplication sendEvent and replaying via CADisplayLink. 2) Unified interceptor – assembly layer reads hardware registers, forwards to C layer which decides replay based on event instructions and re‑injects data into registers/objects. 3) Unified hook for Blocks – converting a block to a structure pointer, replacing its invoke with a unified callback that records/replays the block.

Conclusion: The approach provides low‑intrusion, high‑fidelity issue reproduction and enables future automated testing.