Hi all, FYI i just submitted the below PEP draft to the PEP editors to receive a proper version number. The topics and the draft saw extensive discussions (four versions) on catalog-sig@python.org. We'd like to keep the discussion there if possible. best, holger krekel PEP: XXX Title: Transitioning to release-file hosting on PyPI Version: $Revision$ Last-Modified: $Date$ Author: Holger Krekel <holger@merlinux.eu>, Carl Meyer <carl@oddbird.net> Discussions-To: catalog-sig@python.org Status: Draft (PRE-submit V4) Type: Process Content-Type: text/x-rst Created: 10-Mar-2013 Post-History: Abstract ======== This PEP proposes a backward-compatible two-phase transition process to speed up, simplify and robustify installing from the pypi.python.org (PyPI) package index. To ease the transition and minimize client-side friction, **no changes to distutils or existing installation tools are required in order to benefit from the first transition phase, which will result in faster, more reliable installs for most existing packages**. The first transition phase implements an easy and explicit means for a package maintainer to control which release file links are served to present-day installation tools. The first phase also includes the implementation of analysis tools for present-day packages, to support communication with package maintainers and the automated setting of default modes for controlling release file links. The first phase also will default newly-registered projects on PyPI to only serve links to release files which were uploaded to PyPI. The second transition phase concerns end-user installation tools, which shall default to only install release files that are hosted on PyPI and tell the user if external release files exist, offering a choice to automatically use those external files. Rationale ========= .. _history: History and motivations for external hosting -------------------------------------------- When PyPI went online, it offered release registration but had no facility to host release files itself. When hosting was added, no automated downloading tool existed yet. When Philip Eby implemented automated downloading (through setuptools), he made the choice to allow people to use download hosts of their choice. The finding of externally-hosted packages was implemented as follows: #. The PyPI ``simple/`` index for a package contains all links found by scraping them from that package's long_description metadata for any release. Links in the "Download-URL" and "Home-page" metadata fields are given ``rel=download`` and ``rel=homepage`` attributes, respectively. #. Any of these links whose target is a file whose name appears to be in the form of an installable source or binary distribution, with name in the form "packagename-version.ARCHIVEEXT", is considered a potential installation candidate by installation tools. #. Similarly, any links suffixed with an "#egg=packagename-version" fragment are considered an installation candidate. #. Additionally, the ``rel=homepage`` and ``rel=download`` links are crawled by installation tools and, if HTML, are themselves scraped for release-file links in the above formats. Today, most packages released on PyPI host their release files on PyPI, but a small percentage (XXX need updated data) rely on external hosting. There are many reasons [2]_ why people have chosen external hosting. To cite just a few: - release processes and scripts have been developed already and upload to external sites - it takes too long to upload large files from some places in the world - export restrictions e.g. for crypto-related software - company policies which require offering open source packages through own sites - problems with integrating uploading to PyPI into one's release process (because of release policies) - desiring download statistics different from those maintained by PyPI - perceived bad reliability of PyPI - not aware that PyPI offers file-hosting Irrespective of the present-day validity of these reasons, there clearly is a history why people choose to host files externally and it even was for some time the only way you could do things. This PEP takes the position that there are at least some valid reasons for external hosting. Problem ------- **Today, python package installers (pip, easy_install, buildout, and others) often need to query many non-PyPI URLs even if there are no externally hosted files**. Apart from querying pypi.python.org's simple index pages, also all homepages and download pages ever specified with any release of a package are crawled by an installer. The need for installers to crawl external sites slows down installation and makes for a brittle and unreliable installation process. Those sites and packages also don't take part in the :pep:`381` mirroring infrastructure, further decreasing reliability and speed of automated installation processes around the world. Most packages are hosted directly on pypi.python.org [1]_. Even for these packages, installers still crawl their homepage and download-url, if specified. Many package uploaders are not aware that specifying the "homepage" or "download-url" in their package metadata will needlessly slow down the installation process for all users. Relying on third party sites also opens up more attack vectors for injecting malicious packages into sites using automated installs. A simple attack might just involve getting hold of an old now-unused homepage domain and placing malicious packages there. Moreover, performing a Man-in-The-Middle (MITM) attack between an installation site and any of the download sites can inject malicious packages on the installation site. As many homepages and download locations are using HTTP and not HTTPS, such attacks are not hard to launch. Such MITM attacks can easily happen even for packages which never intended to host files externally as their homepages are contacted by installers anyway. There is currently no way for package maintainers to avoid external-link crawling, other than removing all homepage/download url metadata for all historic releases. While a script [3]_ has been written to perform this action, it is not a good general solution because it removes useful metadata from PyPI releases. Even if the sites referenced by "Homepage" and "Download-URL" links were not scraped for further links, there is no obvious way under the current system for a package owner to link to an installable file from a long_description metadata field (which is shown as package documentation on ``/pypi/PKG``) without installation tools automatically considering that file a candidate for installation. Conversely, there is no way to explicitly register multiple external release files without putting them in metadata fields. Goals ----- These are the goals to be achieved by implementation of this PEP: * Package owners should be able to explicitly control which files are presented by PyPI to installer tools as installation candidates. Installation should not be slowed and made less reliable by extensive and unnecessary crawling of links that package owners did not explicitly nominate as installation files. * It should remain possible for package owners to choose to host their release files on their own hosting, external to PyPI. It should be easy for a user to request the installation of such releases using automated installer tools. * Automated installer tools should not install externally-hosted packages **by default**, but only when explicitly authorized to do so by the user. When tools refuse to install such a package by default, they should tell the user exactly which external link(s) they would need to follow, and what option(s) the user can provide to authorize the tool to follow those links. PyPI should provide all necessary metadata for installer tools to implement this easily and within a single request/reply interaction. * Migration from the status quo to the above points should be gradual and minimize breakage. This includes tooling that makes it easy for package owners with an existing release process that uploads to non-PyPI hosting to also upload those release files to PyPI. Solution / two transition phases ================================ The first transition phase introduces a "hosting-mode" field for each project on PyPI, allowing package owners explicit control of which release file links are served to present-day installation tools in the machine-readable ``simple/`` index. The first transition will, after successful hosting-mode manipulations by individual early-adopters, set a default hosting mode for existing packages, based on automated analysis. **Maintainers will be notified one month ahead of any such automated change**. At completion of the first transition phase, **all present-day existing release and installation processes and tools are expected to continue working**. Any remaining errors or problems are expected to only relate to installation of individual packages and can be easily corrected by package maintainers or PyPI admins if maintainers are not reachable. Also in the first phase, each link served in the ``simple/`` index will be explicitly marked as ``rel="internal"`` (hosted by the index itself) or ``rel="external"`` (linking to an external site that is not part of the index). In the second transition phase, PyPI client installation tools shall be updated to default to only install ``rel="internal"`` packages unless a user specifies option(s) to permit installing from external links. Maintainers of packages which currently host release files on non-PyPI sites shall receive instructions and tools to ease "re-hosting" of their historic and future package release files. This re-hosting tool MUST be available before automated hosting-mode changes are announced to package maintainers. Implementation ============== Hosting modes ------------- The foundation of the first transition phase is the introduction of three "modes" of PyPI hosting for a package, affecting which links are generated for the ``simple/`` index. These modes are implemented without requiring changes to installation tools via changes to the algorithm for generating the machine-readable ``simple/`` index. The modes are: - ``pypi-scrape-crawl``: no change from the current situation of generating machine-readable links for installation tools, as outlined in the history_. - ``pypi-scrape``: for a package in this mode, links to be added to the ``simple/`` index are still scraped from package metadata. However, the "Home-page" and "Download-url" links are given ``rel=ext-homepage`` and ``rel=ext-download`` attributes instead of ``rel=homepage`` and ``rel=download``. The effect of this (with no change in installation tools necessary) is that these links will not be followed and scraped for further candidate links by present-day installation tools: only installable files directly hosted from PyPI or linked directly from PyPI metadata will be considered for installation. Installation tools MAY evolve to offer an option to use the new rel-attribution to crawl external pages but MUST NOT default to it. - ``pypi-explicit``: for a package in this mode, only links to release files uploaded to PyPI, and external links to release files explicitly nominated by the package owner (via a new interface exposed by PyPI) will be added to the ``simple/`` index. Thus the hope is that eventually all projects on PyPI can be migrated to the ``pypi-explicit`` mode, while preserving the ability to install release files hosted externally via installer tools. Deprecation of hosting modes to eventually only allow the ``pypi-explicit`` mode is NOT REGULATED by this PEP but is expected to become feasible some time after successful implementation of the transition phases described in this PEP. It is expected that deprecation requires **a new process to deal with abandoned packages** because of unreachable maintainers for still popular packages. First transition phase (PyPI) ----------------------------- The proposed solution consists of multiple implementation and communication steps: #. Implement in PyPI the three modes described above, with an interface for package owners to select the mode for each package and register explicit external file URLs. #. For packages in all modes, label all links in the ``simple/`` index with ``rel="internal"`` or ``rel="external"``, to make it easier for client tools to distinguish the types of links in the second transition phase. #. Default all newly-registered packages to ``pypi-explicit`` mode (package owners can still switch to the other modes as desired). #. Determine (via an automated analysis tool) which packages have all installable files available on PyPI itself (group A), which have all installable files linked directly from PyPI metadata (group B), and which have installable versions available that are linked only from external homepage/download HTML pages (group C). #. Send mail to maintainers of projects in group A that their project will be automatically configured to ``pypi-explicit`` mode in one month, and similarly to maintainers of projects in group B that their project will be automatically configured to ``pypi-scrape`` mode. Inform them that this change is not expected to affect installability of their project at all, but will result in faster and safer installs for their users. Encourage them to set this mode themselves sooner to benefit their users. #. Send mail to maintainers of packages in group C that their package hosting mode is ``pypi-scrape-crawl``, list the URLs which currently are crawled, and suggest that they either re-host their packages directly on PyPI and switch to ``pypi-explicit``, or at least provide direct links to release files in PyPI metadata and switch to ``pypi-scrape``. Provide instructions and tools to help with these transitions. Second transition phase (installer tools) ----------------------------------------- For the second transition phase, maintainers of installation tools are asked to release two updates. The first update shall provide clear warnings if externally-hosted release files (that is, files whose link is ``rel="external"``) are selected for download, for which projects and URLs exactly this happens, and warn that in future versions externally-hosted downloads will be disabled by default. The second update should change the default mode to allow only installation of ``rel="internal"`` package files, and allow installation of externally-hosted packages only when the user supplies an option (ideally an option specifying exactly which external domains are to be trusted as download sources). When download of an externally-hosted package is disallowed, the user should be notified, with instructions for how to make the install succeed and warnings about the implication (that a file will be downloaded from a site that is not part of the package index). Open Questions / tasks ======================= - Should we introduce some form of PyPI API versioning in this PEP? (it might complicate matters and delay the implementation but is often seen as good practise). - do another round of discussions with installation tool authors and see about incorporating their feedback. There is one known issue in particular from Philip J. Eby who considers a host-based pattern matching algorithm preferable to interpreting "rel" attributes. References ========== .. [1] Donald Stufft, ratio of externally hosted versus pypi-hosted, http://mail.python.org/pipermail/catalog-sig/2013-March/005549.html (XXX need to update this data for all easy_install-supported formats) .. [2] Marc-Andre Lemburg, reasons for external hosting, http://mail.python.org/pipermail/catalog-sig/2013-March/005626.html .. [3] Holger Krekel, Script to remove homepage/download metadata for all releases http://mail.python.org/pipermail/catalog-sig/2013-February/005423.html Acknowledgments ================ Philip Eby for precise information and the basic ideas to implement the transition via server-side changes only. Donald Stufft for pushing away from external hosting and offering to implement both a Pull Request for the necessary PyPI changes and the analysis tool to drive the transition phase 1. Marc-Andre Lemburg, Nick Coghlan and catalog-sig in general for thinking through issues regarding getting rid of "external hosting". Copyright ========= This document has been placed in the public domain.  .. Local Variables: mode: indented-text indent-tabs-mode: nil sentence-end-double-space: t fill-column: 70 coding: utf-8 End: