Displaying images in atom feed - feed

Question

I have problems with displaying images in atom file. It doesn't include images in feed in google reader, opera or firefox.
As a starting point I did everything like in Listing 6. at [An overview of the Atom 1.0 Syndication Format] But it doesn't work.
Update
It is not problem with hotlink protected images. Described here: How to display item photo in atom feed?
Later I changed feed according to description posted here.
I added:
<media:thumbnail xmlns:media="http://search.yahoo.com/mrss/" url="path_to_image.jpg" />
But still it doesn't work

Answer 1

I had the same problem when trying to include images as enclosure, but it seemed that the easiest way for me was to include the image with the normal img tag to the html content.
(It's also wrapped in CDATA, which might affect the way Google Reader handles the content. I haven't tried without.)
The following example works for me to make atom feed images visible in Google Reader:
<content type="html">
<![CDATA[
<a href="http://test.lvh.me:3000/listings/341-test-pics?locale=en">
<img alt="test_pic" src="http://test.lvh.me:3000/system/images/20/medium/test_pic.jpg?1343246102" />
</a>
]]>
</content>

Answer 2

Wordpress uses the metafield enclosure to set the medias. This is the correct tag according to RSS specification. I have seen people suggest using media:content but if using that make sure to set the XML namespace for it.
Unfortunately due to some dodgy Wordpress code you can not set this dynamically. (Wordpress gets all metafields and then loops through them instead of calling the enclosure directly)
You can set the enclosure on save post. It should be an array with entries of the form "$url\n$length\n$type"
If you want to add the enclosure tags yourself you can do the following:
RSS
add_action( 'rss2_item', 'hughie_rss2_item_enclosure' );
function hughie_rss2_item_enclosure():void
{
$id = get_post_thumbnail_id();
$url = wp_get_attachment_url($id);
$length = filesize(get_attached_file($id));
$type = get_post_mime_type($id);
echo apply_filters( 'rss_enclosure', '<enclosure url="' . esc_url( $url ) . '" length="' . absint( $length ) . '" type="' . esc_attr( $type ) . '" />' . "\n" );
}
ATOM:
add_action( 'atom_entry', 'hughie_atom_entry_enclosure' );
function hughie_atom_entry_enclosure():void
{
$id = get_post_thumbnail_id();
$url = wp_get_attachment_url($id);
$length = filesize(get_attached_file($id));
$type = get_post_mime_type($id);
echo apply_filters( 'atom_enclosure', '<link rel="enclosure" href="' . esc_url( $url ) . '" length="' . absint( $length ) . '" type="' . esc_attr( $type ) . '" />' . "\n" );
}
The only way I found to set the enclosure dynamically is short-circuiting the get_metadata call. You can add checks to make sure that you are in a feed or even the check the stacktrace to make sure.
add_filter('get_post_metadata', 'hughie_get_post_metadata', 10, 5 );
function hughie_get_post_metadata($value, int $object_id, string $meta_key, bool $single, string $meta_type)
{
if (is_feed() && $meta_key === '') {
$backtrace = debug_backtrace();
if (isset($backtrace[7]['function']) && ( $backtrace[7]['function'] === 'rss_enclosure' || $backtrace[7]['function'] === 'atom_enclosure' ) ) {
if (!isset($value['enclosure'])) {
$value['enclosure'] = [];
}
$id = get_post_thumbnail_id();
$url = wp_get_attachment_url($id);
$length = filesize(get_attached_file($id));
$type = get_post_mime_type($id);
$value['enclosure'][] = "$url\n$length\n$type";
}
}
return $value;
}