.NET Information center: Metalink

Saturday, October 27, 2012

Metalink

Metalink is a cross-platform and cross-application Internet standard/framework/file format for programs that download, including download managers, BitTorrent clients, Web browsers, FTP clients, and P2P programs. For increased convenience, the multiple download locations for a file (FTP/HTTP/P2P) and other metadata in HTTP header fields and/or an XML file with the extension .meta4 or .metalink. The duplicate download locations provide reliability in case one method fails. Some clients also achieve faster download speeds by allowing different chunks/segments of each file to be downloaded from multiple resources at the same time (segmented downloading).

Other features include automatic hash verification of finished downloads, automatic repair of downloads with errors, listing multiple files to be added to a download queue, and automatic OS/language selection.

Metalink is extensible, and supports listing multiple partial and full file hashes along with PGP signatures. Most clients only support verifying MD5, SHA-1, & SHA-256, however. Besides FTP and HTTP mirror locations and rsync, it also supports listing the P2P methods BitTorrent, ed2k, magnet link or any other that uses a URI.

Example Metalink 4.0 .meta4 file

Metalink 4.0 files have the extension .meta4 and are XML text files. They are served with the application/metalink4+xml Internet media type.

<?xml version="1.0" encoding="UTF-8"?>

<identity>Example</identity>

A description of the example file for download.

</description>

<url location="de" priority="1">ftp://ftp.example.com/example.ext</url>

<url location="fr" priority="1">http://example.com/example.ext</url>

<metaurl mediatype="torrent" priority="2">http://example.com/example.ext.torrent</metaurl>

</file>

</metalink>