added PEP 381 (mirroring infrastructure for PyPI)
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Tarek Ziadé
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PEP: 376
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Title: Mirroring infrastructure for PyPI
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Version: $Revision$
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Last-Modified: $Date$
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Author: Tarek Ziadé <tarek@ziade.org>
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Status: Draft
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Type: Standards Track
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Content-Type: text/x-rst
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Created: 21-March-2009
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Python-Version: N.A.
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Post-History:
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Abstract
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========
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This PEP describes a mirroring infrastructure for PyPI.
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Rationale
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=========
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PyPI is hosting over 4000 projects and is used on a daily basis
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by people to build applications. Especially systems like `easy_install`
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and `zc.buildout` make intensive usage of PyPI.
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For people making intensive use of PyPI, it can act as a single point
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of failure. People have started to set up some mirrors, both private and
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public. Those mirrors are active mirrors, which means that they are
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browsing PyPI to get synced.
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In order to make the system more reliable, this PEP describes:
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- the mirror listing and registering at PyPI
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- the pages a public mirror should maintain.
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these pages will be used by PyPI, in order to get
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hit counts and the last modified date.
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- how a mirror should synchronize with PyPI
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- how a client can implement a fail-over mechanism
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- a contact form for Package maintainers
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Mirror listing and registering
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==============================
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A new text page will be added at `http://pypi.python.org/mirrors`
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that can be browsed like the simple index. This page gives a list of
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the mirrors through a list of links.
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These links are the URL of the simple index of each mirror.
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The page will look like this::
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# PyPI mirrors
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#
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# If you want to register a new mirror, send an email
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# to the catalog-SIG@python.org with:
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#
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# - The urls of your mirror:
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# - the root of the server
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# - the index page
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# - the last modified page
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# - the local stats page
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# - the global stats page
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# - the mirrors page
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#
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# - The name and email of the maintainer.
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#
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# The registering is done manually and to become a
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# mirror, you need to strictly follow the mirror protocol
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# described here:
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#
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# http://wiki.python.org/PEP_374
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#
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# root,index,last-modified,local-stats,stats,mirrors
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http://example.com/pypi,index,last-modified,local-stats,stats,mirrors
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http://example2.com/pypi,index,last-modified,local-stats,stats,mirrors
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When a mirror is proposed on the mailing list, it is manually
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added in the mirror list in the PyPI application after it
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has been checked to be compliant with the mirroring rules.
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The mirror list page is a simple text page that can be browsed
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by any tool that wants to get a list of registered mirrors.
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Other package indexes that are not mirrors of PyPI are not added in the
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mirror list in PyPI. Although they can provide themselve the
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same mirroring list mechanism for their own mirrors.
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Special pages a mirror needs to provide
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=======================================
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A mirror needs to provide four pages, beside the index one:
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- last-modified
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- local-stats
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- stats
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- mirrors
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Last modified date
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::::::::::::::::::
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CPAN uses a freshness date system where the mirror last synchronisation
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date is made available.
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For PyPI, each mirror needs to maintain an url with a simple text content
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that represents the last synchronisation date the mirror maintains.
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The date is provided in GMT time, using the ISO 8601 format
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(see http://en.wikipedia.org/wiki/ISO_8601)
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Each mirror will be responsible to maintain its last modified date.
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Conventionaly, this page should be reachable at: `/last-modified`.
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Local statistics
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::::::::::::::::
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Each mirror is responsible to count all the downloads
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that where done on it. This is used by PyPI to sum up all
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downloads, to be able to display the grand total.
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These statistics are in csv-like form, with a header at the first
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line. It needs to obey `PEP 305 <http://www.python.org/dev/peps/pep-0305/#id19>`_
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Basically, it should be readable by Python `csv` module.
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The fields in this file are:
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- package: the distutils id of the package.
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- filename: the filename that has been downloaded.
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- useragent: the User-Agent of the client that has downloaded the package.
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- count: the number of downloads.
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The content will look like this::
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# package,filename,useragent,count
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zc.buildout,zc.buildout-1.6.0.tgz,MyAgent,142
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...
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The counting starts the day the mirror is launched, and there is one file per
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day, compressed using the `bzip2` format. Each file is named after the
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day. For example `2008-11-06.bz2` is the file for the 6th of November 2008.
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They are then provided in a folder called `days`. For example:
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- /local-stats/days/2008-11-06.bz2
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- /local-stats/days/2008-11-07.bz2
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- /local-stats/days/2008-11-08.bz2
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Conventionally the name should be `local-stats` but it can be any name
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provided when the mirror is registered.
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Statistics page
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:::::::::::::::
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PyPI and each mirror are responsible to provide the grand total
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page at `/stats`. This page is calculated daily by PyPI,
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by reading all mirrors local stats and suming them.
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Therefore the mirrors should not try to rebuild this stat page but simply
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get PyPI's one during each synchronization.
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It has the same structure than `local-stats` but also provides
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counts for months.
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Examples:
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- /stats/days/2008-11-06.bz2
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- /stats/days/2008-11-07.bz2
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- /stats/days/2008-11-08.bz2
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- /stats/months/2008-11.bz2
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- /stats/months/2008-10.bz2
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Conventionally the name should be `stats` but it can be any name
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provided when the mirror is registered.
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Mirrors listing page
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::::::::::::::::::::
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Like `/stats`, each mirror should get and provide a copy of the `/mirrors`
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page.
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Conventionally the name should be `mirrors` but it can be any name
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provided when the mirror is registered.
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How a mirror should synchronize with PyPI
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=========================================
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A mirroring protocol calls `Simple Index` was described
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and implemented by Martin v. Loewis and Jim Fulton, based on
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how `easy_install` works. This section synthesizes it
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and give a few relevant links, plus a small part about
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`User-Agent`.
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The mirroring protocol
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::::::::::::::::::::::
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XXX Need to describe the protocol here.
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The `zc.pypimirror <http://pypi.python.org/pypi/z3c.pypimirror>`_ package
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provides an application that respects this protocol to browse PyPI.
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User-agent request header
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:::::::::::::::::::::::::
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In order to be able to differentiate actions taken by clients
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over PyPI, a specific user agent name should be provided by all
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mirroring softwares.
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This is also true for all clients like:
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- `zc.buildout <http://pypi.python.org/pypi/zc.buildout>`_
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- `setuptools <http://pypi.python.org/pypi/zc.buildout>`_
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- `pip <http://pypi.python.org/pypi/zc.buildout>`_
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- etc.
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XXX user agent registering mechanism at PyPI ?
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How a client can use PyPI and its mirrors
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:::::::::::::::::::::::::::::::::::::::::
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Clients that are browsing PyPI should be able to use
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alternative mirrors, by reading the `/mirrors` page
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at PyPI.
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The clients so far that could use this mechanism:
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- setuptools
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- zc.buildout (through setuptools)
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- pip
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Fail-over mechanism
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:::::::::::::::::::
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Clients that are browsing PyPI should be able to use
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a fail-over mechanism when PyPI or the used mirror
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is not responding.
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This can be done by parsing the `/mirrors` page of PyPI
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or the one located on any PyPI mirror.
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It is up to the client to decide wich mirror should
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be used. Maybe by looking at its geographical location and
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its responsivness.
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This PEP does not describe how this fail-over
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mechanism should work, but it is strongly encouraged
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that the clients try to use the nearest mirror.
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The clients so far that could use this mechanism:
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- setuptools
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- zc.buildout (through setuptools)
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- pip
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Extra package indexes
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:::::::::::::::::::::
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It is obvious that some package will not be uploaded
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to PyPI. Wether because they are private or wether because
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the project maintainer runs his own server where people
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might get the project package. Although, it is strongly
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encouraged that a public package index follows PyPI
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and Distutils protocols.
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In other words, the `register` and `upload` command
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should be compatible with any package index server out
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there.
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Softwares that are compatible with PyPI and Distutils so
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far:
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- `PloneSoftwareCenter <http://plone.org/products/plonesoftwarecenter>`_
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wich is used to run plone.org products section.
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- `EggBasket <http://www.chrisarndt.de/projects/eggbasket>`_
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**An extra package index is not a mirror or PyPI but can have itself
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some mirrors**
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Merging several indexes
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:::::::::::::::::::::::
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When a client needs to get some packages from several
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distinct indexes, it should be able to use each one of them
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as a potential source of packages. Different indexes
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should be defined as a sorted list for the client to
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look for a package.
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Each independant index can of course provide a list of
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its mirrors, if the `/mirrors` page is available.
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That permits all combinations at client level, for a reliable
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packaging system with all levels of privacy.
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It is up the client to deal with the merging.
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Copyright
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=========
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This document has been placed in the public domain.
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..
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Local Variables:
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mode: indented-text
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indent-tabs-mode: nil
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sentence-end-double-space: t
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fill-column: 70
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coding: utf-8
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End:
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