How to add that missing logging code to your application after it's in the wild

Logging Woes

Logging is one of those aspects of coding that has always bothered me. It's partly because I hate taking the time to write it, and partly because it can really clutter up otherwise clear code. But mostly it's because anytime I've looked through a log file, trying to figure out why the whozit widget is throwing a null reference exception in the whatzit routine, I end up spending what seems like an eternity sifting through gazillions of mind numbing lines of log files, most of which have no bearing on the issue at hand. And, when I do narrow my hunt down to the appropriate part of the file, I find another surprise. The function I really need info about either seems to be missing all together, or the piece of info that I need isn't included in the logging for that function. Now, what do I do? Well, first, I curse the programmer who wrote this routine… until I realize it was me. Great! Now what? If the bug in question is part of some "live" code, it's not really feasible to quickly code in the logging code that I need, rebuild, and reinstall (or at least not very smart). Depending on the scenario, I may be able to attach a debugger, but that's not always realistic either. I can't really add a break point that stops all code execution in a high traffic web site. So, what now?

A Solution

Logger is an application designed to solve this very issue. Install, select the application you would like to log, select the functions you'd like to log, and start logging. Logger will now generate your missing log info for you. No recompile needed. I can now find the bug (duh, what was I thinking when I wrote that code anyway?), fix it, and still make it home before the kids drive my wife crazy.

How it Works

Logger uses a technique known as "IL Rewriting" to dynamically insert logging code into applications at run time. IL rewriting uses the .NET Profiling API to grab code just before it's JITed. It then alters the IL to include the needed logging code before sending it back on its merry way to the .NET runtime. This technique has the advantage of having a very small performance footprint while at the same time not ever actually altering your binary files.

For a more technical discussion on how this works, see my previous article (from a very rough draft of this application) at Really Easy Logging using IL Rewriting and the .NET Profiling API. Also, check out software.herbrandson.com to watch for updates.