This document attempts to explain how to fix the problems associated with the patcher used for World of Warcraft by Blizzard. It does so by explaining alternative ways to do the same thing, not how to recode the patcher.
WoW uses several different methods to update the game. Small patches are downloaded as data files. When the download is complete, a program in the game's directory patches that data into your installation. The download is done from inside the game, and it begins patching files as soon as the game has exited. These patch files are rather small, so they don't present much of a problem, even for dialup users.
The larger WoW patches which tend to include new content and major features are distributed in a different way. A small file is downloaded inside the game as with the minor patches. However, this file is a downloader. When the game exits, this downloader is run. The downloader then attempts to fetch the actual game update, which can be 50MB or more. The downloader can download data directly from patch servers at a fairly low speed or from other users downloading the patch. It uses BitTorrent for this peer-t