Debugging file corruption on iOS

This is the challenge of modern software development. When I first started my career, I spent two months looking for a random crashing bug in a video game due to misplaced free(); this was in code that was 100% ours. Now, there likely isn't an application in existence that does anything interesting where 100% of the code was written for the app itself. As such, you are no longer debugging your own code, but other people's as well.

Vernor Vinge coined the idea of a software archeologist, people who could sift through layers of code, all the way back to the beginning of time (Jan 1, 1970 and Unix, of course), to understand how systems work and to make modifications to them. We aren't that far from that point; already, there are people who seem to specializing in digital spelunking to find and fix bugs in these underlying layers.

While I love building new code, some of the most satisfying moments in my career have been when I've gone back through somebody else's code, untied it (oh, you built a polymorphic type system including class initializers and destructors in a decidedly not object oriented language? Cool.) and fixed it. There's something interesting about getting into somebody else's head and seeing how they approached the problem, then finding out where they were wrong.

> "The SSL layer instead handled a raw file descriptor and, consequently, lifetime handling was not automatically synchronized ... We worked with the networking team and fixed this issue within hours."

Why on earth is Facebook writing their own SSL layer for iOS?

  > // setup a honeypot file
  > int trap_fd = open(…); 
  > // Create new function to detect writes to the honeypot
  > static WRITE_FUNC_T original_write = dlsym(RTLD_DEFAULT, "write");;
  > ssize_t corruption_write(int fd, const void *buf, size_t size) { 
  >   FBFatal(fd != trap_fd, @"Writing to the honeypot file");
  > }
  > return original_write(fd, buf, size);
  > }
  > // Replace the system write with our “checked version”
  > rebind_symbols((struct rebinding[1]){{(char *)"write", (void *)corruption_write}}, 1);

Does this code snippet look fishy to anyone else? First, the mismatch braces are messing with my head. I'm thinking the brace before the return is a typo. Also, the call to the macro looks wrong. Shouldn't they be checking for fd == trap_fd?

I would love to see a standalone testcase demonstrating this bug. Although, what was Facebook's solution to fix it? Was it to make a fix to the SSL library to use a CFSocker wrapper?

| It turns out that abandoning manual code analysis was a good strategy.

Wait a minute, wasn't this manual code analysis? They were certainly digging around the codebase and a particular slice of commits to figure out why the crash kept occurring.

Move fast and break things.

i feel they are just over complicating.