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= How to avoid master_sites redirects  =

 * Audience: Portfile authors 
 * Requires: MacPorts >=2.0

== Introduction ==

`master_sites` should usually be specified in such a way that HTTP redirects are avoided.
This not only reduces network traffic and server load but also lets the user start their download more quickly.
This how-to currently addresses only SourceForge but similar techniques can be used for any other site.

== SourceForge ==

In addition to the aforementioned general reasons for avoiding redirects, it's especially important for files hosted at SourceForge.
For all ports, MacPorts tries to download from a server near to the user (measured by ping time).
SourceForge has a network of mirror servers, of which MacPorts maintains [browser:trunk/dports/_resources/port1.0/fetch/mirror_sites.tcl a list].
But if the server MacPorts has chosen to use issues a redirect, it might redirect to a different server which might have a worse ping time, which we want to avoid.

Hopefully, the following example, using mediainfo version 0.7.60, will illuminate the process.  The SourceForge home page for mediainfo is [[http://mediainfo.sourceforge.net]].  Initially, just specifying  `'sourceforge'` in the portfile under development worked to retrieve the distfile.  

{{{
master_sites  sourceforge
}}}

The log for `'port fetch'` showed:

{{{
DEBUG: Executing org.macports.fetch (mediainfo)
--->  MediaInfo_CLI_0.7.60_GNU_FromSource.tar.bz2 doesn't seem to exist in /opt/local/var/macports/distfiles/mediainfo
--->  Attempting to fetch MediaInfo_CLI_0.7.60_GNU_FromSource.tar.bz2 from http://iweb.dl.sourceforge.net/mediainfo
}}}

Use `curl -IL http://iweb.dl.sourceforge.net/mediainfo/MediaInfo_CLI_0.7.60_GNU_FromSource.tar.bz2` to check for redirects.  In this case the output indicated redirects to a final address of:

{{{
Location: http://voxel.dl.sourceforge.net/project/mediainfo/binary/mediainfo/0.7.60/MediaInfo_CLI_0.7.60_GNU_FromSource.tar.bz2
}}}

To improve the `master_sites` parameter, extract the bit: `project/mediainfo/binary/mediainfo/0.7.60` (and replace "0.7.60"--the version number in this case--with ${version}).  Thus you have:

{{{
master_sites  sourceforge:project/mediainfo/binary/mediainfo/${version}
}}}

In the event that the URL had included "0.7" (and not "0.7.60") you would want to define and employ [PortfileRecipes#branch the ${branch} variable] instead of ${version}.

Pat yourself on the back--you're done!

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