How should I implement an auto-updater?

Question

Many programs include an auto-updater, where the program occasionally looks online for updates, and then downloads and applies any updates that are found. Program bugs are f

Answer 1

This is not so much a complete answer, but rather one example of auto-updating mechanism I implemented recently. The situation is a little different from the tradition Firefox-type of user application, since it was an internal tool used at work.

Basically, it's a little script that manages a queue of Subversion branches to be built and packaged in an installer. It reads a little file, where the names of the branches are written, takes the first one, re-writes it at the end of the file, and launches the build process, which involves calling a bunch of scripts. The configuration for each branch to build is written in a .INI file, stored in a Subversion repository along with the tool itself.

Because this tool runs on several computers, I wanted a way to update it automatically on all machines as soon as I made a change either to the tool itself, or to the configuration scripts.

The way I implemented it was simple: when I launch the tool, it becomes an "outer shell". This outer shell does 2 very simple things:

• svn update on itself and on the configuration files
• launch itself again, this time as the "inner shell", the one that actually handles one configuration (and then exits again).

This very simple update-myself-in-a-loop system has served us very well for a few months now. It's very elegant, because it is self-contained: the auto-updater is the program itself. Because "outer shell" (the auto-updater part) is so simple, it doesn't matter that it does not benefit from the updates as the "inner shell" (which gets executed from the updated source file every time).