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Design Document: Magnet links

The Magnet a URI scheme is an open standard which specifies a file to be downloaded, but not how the file should be downloaded. Basic magnet link support will be available in Miro 4.0. This design document covers what and how it is supported.

Requirements, Use Cases and User Stories

Michaela is surfing the web and does not know what a magnet link is, but clicks on the link and wants everything to work.

Monica gets sent a magnet link from her friend and wants to download it with Miro.

Peter already has the magnet.exe utility on his computer without knowing because it was delivered with other BitTorrent clients. He installs Miro and wants to be able to choose Miro when clicking on a magnet link.

Diana is a power user and uses Miro and other BitTorrent applications side by side and wants to be able to choose which application to use when clicking on a Magnet link. So she installs the magnet.exe utility.

Research Links

Wikipedia article on the Magnet URI scheme:

magnet.exe utility.

Best source on magnet info hash encoding I have been able to find.

The comments for bug 16794 have details on magnet info hash encoding issues.


What is supported

Miro only supports torrent magnet links. This means magnet links of the following format:


Where BITTORENT_INFO_HASH is a hex or base32 encoded BitTorrent info hash (in other BitTorrent applications info hashes usually hex encoded).

Ways to download magnet links in Miro 4.0:

Other download methods are not yet supported.

The Miro downloader

Libtorrent supports magnet links.The majority of the magnet work is making the Miro downloader support magnet links. The main problem is that torrents added through a magnet link only receive their metadata after the download is started in libtorrent.

Procedure for torrent downloads:

  1. get torrent link
  2. download torrent file
  3. extract metadata
  4. begin download

Procedure for magnet downloads:

  1. get magnet link
  2. begin download
  3. extract metadata

This changed procedure requires quite some changes in the downloader codebase.

Association policies

Windows and Linux

Miro checks the association at each startup and associates with the magnet protocol if no other program is associated already.

Windows only


Windows apparently only can associate with one application at once with a protocol. To solve this one can install the tool magnet.exe and associate it with the magnet protocol. Applications which can handle the magnet protocol can then register with magnet.exe. When the user clicks on a magnet link, the magnet.exe tool is run and presents the user with a list of all programs which can handle magnet links.

Miro always tries to register with magnet.exe, even if magnet.exe is not installed. However because of security restrictions, it is not possible to register on Windows Vista or newer, since magnet.exe only works with HKEY_LOCAL_MACHINE.

Keys for magnet association

In Gconf

On Windows

This is a short and incomplete overview of which registry keys are used on Windows. The values set are not written down here.

Magnet.exe keys:

Possible todos

Personal tools