## page was renamed from Mirrorring infrastructure
## page was renamed from Mirroriing infrastructure
## page was renamed from PEP 374
= Mirroring infrastructure in PyPI =

 * PEP: xx
 * Title: Mirroring infrastructure in PyPI
 * Author: Tarek Ziadé
 * Discussions-To: Catalog SIG
 * Status: Draft
 * Python-Version: 2.6

== Abstract ==

This PEP describes a mirroring infrastructure for PyPI.

== Motivations ==

PyPI is hosting over 4000 projects and is used on a daily basis 
by people to build applications. Especially systems like easy_install
and zc.buildout make intensive usage of PyPI.

For people making intensive use of PyPI, it can act as a single point
of failure. People have started to set up some mirrors, both private and
public. Those mirrors are active mirrors, which means that they are
browsing PyPI to get synced. 

In order to make the system more reliable, this PEP describes:

- the mirror listing and registering at PyPI 

- the pages a public mirror should maintain. 
  these pages will be used by PyPI, in order to get 
  hit counts and the last modified date.

- how a mirror should synchronize with PyPI

- how a client can implement a fail-over mechanism

- a contact form for Package maintainers

== Mirror listing and registering ==

A new text page will be added at http://pypi.python.org/mirrors
that can be browsed like the simple index. This page gives a list of
the mirrors through a list of links.

These links are the URL of the simple index of each mirror.
The page will look like this:

{{{
# PyPI mirrors
#    
# If you want to register a new mirror, send an email
# to the catalog-SIG@python.org with:
#
# - The urls of your mirror:
#   - the root of the server
#   - the index page 
#   - the last modified page
#   - the local stats page
#   - the global stats page
#   - the mirrors page
#
# - The name and email of the maintainer.
#   
#   The registering is done manually and to become a
#   mirror, you need to strictly follow the mirror protocol
#   described here:
#
#    http://wiki.python.org/PEP_374
#    
# root,index,last-modified,local-stats,stats,mirrors
http://example.com/pypi,index,last-modified,local-stats,stats,mirrors
http://example2.com/pypi,index,last-modified,local-stats,stats,mirrors
}}}

When a mirror is proposed on the mailing list, it is manually
added in the mirror list in the PyPI application after it
has been checked to be compliant with the mirroring rules.

The mirror list page is a simple text page that can be browsed 
by any tool that wants to get a list of registered mirrors.
Other package indexes that are not mirrors of PyPI are not added in the 
mirror list in PyPI. Although they can provide themselve the 
same mirroring list mechanism for their own mirrors.

== Special pages a mirror needs to provide ==

A mirror needs to provide four pages, beside the index one:

 * last-modified
 * local-stats
 * stats
 * mirrors
 
=== Last modified date ===

CPAN uses a freshness date system where the mirror last synchronisation 
date is made available.

For PyPI, each mirror needs to maintain an url with a simple text content
that represents the last synchronisation date the mirror maintains.

The date is provided in GMT time, using the iso 8601 format
(http://en.wikipedia.org/wiki/ISO_8601)

Each mirror will be responsible to maintain its last modified date. 

Conventionaly, this page should be reachable at: "/last-modified".

=== Local statistics ===

Each mirror is responsible to count all the downloads
that where done on it. This is used by PyPI to sum up all
downloads, to be able to display the grand total.

This page is a csv-like page, with a header at the first 
line. It needs to obey PEP 305 http://www.python.org/dev/peps/pep-0305/#id19.
Basically, it should be readable by Python csv module.

The fields in this file are:

 * package: the distutils id of the package.
 * filename: the filename that has been downloaded.
 * useragent: the User-Agent of the client that has downloaded the package.
 * count: the number of downloads.

The page will look like this:

{{{
# package,filename,useragent,count
zc.buildout,zc.buildout-1.6.0.tgz,MyAgent,142
...
}}}

The counting starts the day the mirror is launched.

Conventionaly, this page should be reachable at: "/local-stats", but any url relative to the mirror root can be given.

=== Statistics page ===

PyPI and each mirror are responsible to provide the grand total
page at "/stats". This page is calculated daily by PyPI,
by reading all mirrors local stats and suming them. 

Therefore the mirrors should not try to rebuild this stat page but simply
get PyPI's one during each synchronization.

It has the same structure than the local-stats page.

Conventionaly, this page should be reachable at: "/stats".

=== Mirrors listing page ===

Like /stats, each mirror should get and provide the /mirrors
page.

Conventionaly, this page should be reachable at: "/mirrors".

== How a mirror should synchronize with PyPI ==

A mirroring protocol calls Simple Index was described 
and implemented by Martin v. Loewis and Jim Fulton, based on 
how easy_install works. This section synthesizes it
and give a few relevant links, plus a small part about 
User-Agent.

=== The mirroring protocol ===

XXX changelog, pje link + to be defined

=== User-agent request header ===

In order to be able to differentiate actions taken by clients
over PyPI, a specific user agent name should be provided by all 
mirroring softwares.

This is also true for all clients like:

 * zc.buildout
 * setuptools
 * pyinstaller
 * etc.

XXX user agent registering mechanism at PyPI ?

== How a client can use PyPI and its mirrors ==

XXX

== Fail-over mechanism ==

Clients that are browsing PyPI should be able to use 
a fail-over mechanism when PyPI is not responding.

This can be done by parsing the /mirrors page of PyPI
or the one located on any PyPI mirror. 

It is up to the client to decide wich mirror should
be used, depending on its geographical location and
its responsivness.

This PEP does not describe how this fail-over
mechanism should work, but it is strongly encouraged
that the clients try to use the nearest mirror.

The clients so far that could use this mechanism:

 * setuptools
 * zc.buildout (through setuptools)
 * pyinstaller

== Extra package indexes ==

It is obvious that some package will not be uploaded
to PyPI. Wether because they are private or wether because
the project maintainer runs his own server where people
get the project package. Although, it is strongly
encouraged that a public package index follows PyPI
and distutils protocols. In other words, the "register"
and "upload" command should be compatible with any 
package index server out there.

Softwares that are compatible with PyPI and distutils:

 * PloneSoftwareCenter
 * EggBasket

== Merging several indexes ==

When a client needs to get some packages from several 
distinct indexes, it should be able to use each one of them
as a potential source of packages. Different indexes
should be defined as a sorted list for the client to
look for a package.

Each independant index can of course provide a list of 
its mirrors, if the /mirrors page is available.

That permits all combinations at client level, for a reliable
packaging system with all levels of privacy.

== Other PyPI enhancements ==

XXX

=== Contact form for Package maintainers ===

A form reachable from the package page will be added,
where a registered user can submit a message to the package
owner. This is to be used when someone wants to take over
the distutils id name, or when someone (like a packager
for example) would like to reach the package owner 
for some questions.

XXX isn't the mail in the metadata enough ?
XXX the original whish here was to enforce the package owner
to upload sdist.