debug

Following on from last week’s blog, this will cover monitoring an iPhone’s HTTPS traffic. If you haven’t already, look at the setup from last week as it is required in order for this next part to work.

Previously when I’ve needed to monitor web traffic from my iPhone I would use my laptop to redistribute my wifi as a 2nd network with another network card and use a tool like WireShark or Charles to monitor everything that’s being sent and received from my iPhone after I connected to the 2nd network. This was overcomplicating things, hidden in the iPhone’s settings is the ability to connect to a proxy server, meaning you can debug web traffic without the need for any 2nd networks or ethernet cables.

Since Xcode 4.1 when your application throws an exception your console just prints a list of function pointers and you don’t get a proper stack trace. This isn’t helpful if you’re trying to find the exact line the error occurred on.

If you have ever needed to store a password or other sensitive data in an iPhone app, you have probably used Keychain Access, Apple’s solution to storing data securely. You have also probably used Apple’s KeychainWrapper class, offering a very easy wrapper to storing info in the keychain.

The KeychainWrapper worked well in debug mode, but when building for release it didn’t seem to be writing objects to the keychain. I was fumbling around with this for hours, going over my own code thinking I had made a mistake somewhere. In the end I figured out what the problem was, in Apple’s code for KeychainWrapper the actual line that executed the commit to the keychain was inside an NSAssert, which is used for development, but as soon as you build for release or distribution every NSAssert is nullified, giving the same effect of commenting out anything on that line, removing the keychain commit code.