Blizzard Downloader

Blizzard Downloader (or Background Downloader) is a combination BitTorrent/HTTP client used for Blizzard Entertainment's software products. It was first implemented with MMORPG World of Warcraft. It is used to download full game installer package or large updates for the game, smaller updates being downloaded directly from the server. It is also used to download the trailers for The Burning Crusade and StarCraft II. Early versions were based on the source code of the original BitTorrent client, though it is unclear what the source model is now. When a large update is issued a Blizzard Downloader is downloaded to the WoW directory and it fetches the update file, using TCP ports 3724 and 6881. Blizzard offers an individual client for each download they offer, instead of just a torrent file. The Blizzard downloader also runs in the background under the name of "Background Downloader." While the downloader is running, the program also uploads parts of files over the internet to other users who need the same data.

Structure
The Blizzard Downloader bundle is actually a plain BitTorrent client that has at least one .torrent file inside. The .torrent can be opened by other BitTorrent clients giving the user greater control over how the download is handled.

It is possible to extract the .torrent file from the end of the downloader executable:

Windows version
*Search for d8:announce at the end of the downloader executable, and then save from this point to the end of the executable to a separate file. Add .torrent to the file name and open in any BitTorrent Client.
*Note that these executables may contain multiple torrent files (e.g. the Burning Crusade Downloader contains a 'slim' torrent 1.24 GB and a 'full' torrent for 2.23 GB).

Earlier versions included a Macintosh-variant of the .torrent as well, but this has been removed in later versions. You may also need to remove some trailing characters at the end of the file, since they do not all belong to the .torrent; essentially, the resulting file has to be Bencode-compliant.

Alternatively, start the background downloader and check the end of Logs\BackgroundDownload.log for a message like this:

*Creating cache file C:\Program Files\World of Warcraft\Cache\BackgroundDownload.torrent

This .torrent file can be used with any BitTorrent client. Alternate locations may include the Cache folder, depending on the WoW client's locality.

Macintosh version

*/Applications/World of Warcraft/WoW-old-to-new-local-downloader.app/Contents/
**MacOS/
***Blizzard Downloader - executable file
**Resources/
***downloader.torrent - torrent file
:Note: GUI & localization files not listed for readability.

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See Also

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