Allow multiple enclosures in Atom feeds

[Piaume]

For now, Feed.item_enclosure_url represents a single enclosure for an item. It should be nice to support many enclosures per item. Something like that:

class ExampleFeed(Feed):
    def item_enclosure_url(self, item):
        return [video.url for video in item.videos]

[Eric Holscher]

Feature Request.

[Jason Kotenko]

It appears that RSS only officially supports one enclosure per item {1}, and Atom supports multiple. Since RSS is the default feed, actually the use case presented in the bug report is invalid. The question then becomes, should we support multiple enclosures for Atom? As of now the enclosure is handled in the same general way in both types of feeds.

Changing to "Design Decision Needed" before I do anything else... Please let me know if that was the wrong thing to do in this situation, as I'm pretty new to the Django community.

{1} - ​http://www.rssboard.org/rss-profile#element-channel-item-enclosure

[Aymeric Augustin]

It should be possible to accept either a string or a list of string, and to validate that there's only one enclosure for RSS feeds.

[Unai Zalakain]

Replying to aaugustin:

It should be possible to accept either a string or a list of string, and to validate that there's only one enclosure for RSS feeds.

Currently Feed builds the Enclosure from item_enclosure_url, item_enclosure_length and item_enclosure_mime_type. Accepting an optional list for one of them would mean accepting optional lists for the three of them and that would become quite a strange and cumbersome API.

Instead, I propose creating a item_enclosures attr/func (the same way all the other attr/funcs work) which, by default, returns a list with a single Enclosure in it. That enclosure would be built using the url, length and mime_type gotten from the corresponding attrs.

RSS feeds could then validate that item_enclosures is no longer than 1.

[Unai Zalakain]

Could something along these lines be enough?
​https://github.com/unaizalakain/django/commit/9acc50df64408d4023378ae4259fa1069b215ab2

[Unai Zalakain]

I updated the commit with the proposed changes and opened a PR:
​https://github.com/django/django/pull/5200

[Unai Zalakain]

Updated PR with docs.

[Unai Zalakain]

Basic tests added, PR updated, ready for review!

[Tim Graham]

I left comments for improvement on the pull request.

[Unai Zalakain]

PR updated!

[Tim Graham <timograham@…>]

In aac2a2d:

Fixed #13110 -- Added support for multiple enclosures in Atom feeds.

The item_enclosures hook returns a list of Enclosure objects which is
then used by the feed builder. If the feed is a RSS feed, an exception is
raised as RSS feeds don't allow multiple enclosures per feed item.

The item_enclosures hook defaults to an empty list or, if the
item_enclosure_url hook is defined, to a list with a single Enclosure
built from the item_enclosure_url, item_enclosure_length, and
item_enclosure_mime_type hooks.

[Tim Graham]

Reopening per comments on the commit.

[Unai Zalakain]

Sorry about that…
New PR: ​https://github.com/django/django/pull/5315

[Unai Zalakain <unai@…>]

In a4b80e24:

Refs #13110 -- Fixed mistakes in the new multiple enclosure feed tests

[Tim Graham <timograham@…>]

In 2ec23a3d:

Refs #13110 -- Fixed typo in Feed class reference.

[Tim Graham <timograham@…>]

In 54295a95:

[1.9.x] Refs #13110 -- Fixed typo in Feed class reference.

Backport of 2ec23a3d41be2ba5df9f46b17e0a05eb1b051c41 from master

[Tim Graham <timograham@…>]

In 75cf9b5a:

Refs #13110 -- Removed SyndicationFeed.add_item()'s enclosure argument.

Per deprecation timeline.