Metalink

Metalink is an open standard/framework for programs that download (download managers, BitTorrent clients, Web browsers, FTP clients, & P2P programs). For increased convenience, it stores the many locations of files (FTP/HTTP/P2P) in a single file (a .metalink) so chunks/segments of each file can be downloaded from multiple resources at the same time (known as accelerated/multi-threaded/segmented downloading). If you have a fast Internet connection, this usually results in a more reliable and much faster download than a typical single segment download from one server. Other features include automatic checksum comparison of finished downloads, and automatic OS/language selection. Metalinks are also backwards compatible with regular hyperlinks by using the format http://URL#!metalink3!http://URLtoMetalink.

Metalink is extensible, and supports listing MD5 & SHA-1 checksums along with PGP signatures. Besides FTP and HTTP mirror locations and rsync, it also supports listing these P2P methods: BitTorrent, ed2k, and magnet link.

Client programs

• aria2 (GPL) is a Unix command line "high speed download utility" that supports BitTorrent and Metalink (HTTP/FTP/BitTorrent).
• FlashGot (GPL), a Firefox extension for integrating with many Download Managers, supports Metalink.
• GetRight 6, a Windows Download Manager, supports Metalink.
• Speed Download, a Mac Download Manager, supports Metalink as of version 4.1.0.
• wxDownload Fast (GPL) is a Mac/Unix/Windows download manager that supports Metalink.

See a Comparison of download managers for details on which of them support Metalink and have other features.

In use

Currently, OpenOffice.org uses Metalinks on an alternate P2P download page with Magnet links.

The following distributions use Metalink for ISO distribution: Arch Linux, DesktopBSD, PC-BSD, BLAG Linux and GNU, StartCom Enterprise Linux, Berry Linux, Ubuntu Christian Edition, PuppyLinux.

Metalink generation

Metalink is XML so they can be hand crafted or XML tools can be used for automation. These tools are specifically for Metalink.

• Simba (GPL), the mirroring tool, includes automatic Metalink generation as one of its features. There are are special Metalink plugins available for it.

• Metalink Generator can also be used to create Metalinks by filling out a form.

Example .metalink file

.metalinks are XML text files.

<metalink version="3.0" xmlns="http://www.metalinker.org/">
  <files>
    <file name="example.ext">
    <verification>
      <hash type="md5">example-md5-hash</hash>
      <hash type="sha1">example-sha1-hash</hash>
    </verification>
    <resources>
      <url type="ftp">ftp://ftp.example1.com/example.ext</url>
      <url type="ftp">ftp://ftp.example2.com/example.ext</url>
      <url type="http">http://www.example1.com/example.ext</url> 
      <url type="http">http://www.example2.com/example.ext</url>
      <url type="http">http://www.example3.com/example.ext</url> 
      <url type="bittorrent">http://www.ex.com/example.ext.torrent</url>
      <url type="magnet"/>
      <url type="ed2k"/>
    </resources>
    </file>
  </files>
</metalink>

Blog descriptions

TorrentFreak explains Metalink like this: "We’ve all seen those download pages where a couple of http, ftp and bittorrent mirrors are listed. We often just pick one of these, but wouldn’t it be great if you could use them all at the same time? Metalink has the solution. It works like this, the .metalink file tells your download manager where it can get the file, and connects to these different sources at the same time."

downloadsquad describes it this way: "Metalinks make complex download pages obsolete by replacing long lists of download mirrors and BitTorrent trackers with a single .metalink file. As you might have already guessed, a .metalink file is a file that tells a download manager all the different ways it can download a file. The file itself takes the form of an open XML standard that can list an unlimited number of HTTP and FTP sources as well as BitTorrent trackers and ed2k and magnet links."

External links

• Metalink homepage
• Metalink @ Packages Resources : Automatically generated Metalinks for Open Source software along with source code for the Metalink generator.
• Simba (GPL), the mirroring tool.
• OpenOffice.org P2P page