Debugging file corruption on iOS

What this post added

This post details the debugging process for a file corruption issue on iOS affecting the Facebook app. It describes the use of Hipal and Scuba for crash report analysis, the hypothesis-driven approach to isolate the cause (switching from Core Data to SQLite), the 'honeypot' file technique to detect rogue writes, the use of lldb for conditional breakpoints on the `write` system call, and the application of Fishhook to rebind system APIs for direct proof of the networking stack writing to a closed socket that was reassigned to the database file. The root cause was identified as a file descriptor lifetime handling issue in the SSL layer of the SPDY network stack.