Using phpBB 3.1.5 with the built-in Atom feeds, inline image attachments use relative links.
For an example, please see http://forum.cafu.de/feed.php?mode=news
Its source code contains:
<img src="./download/file.php?id=259&t=1&sid=e274fff03c06a976c0d1ccb67985bbad" class="postimage" alt="BPWxBeta_MasterLift.jpg" title="BPWxBeta_MasterLift.jpg (16.29 KiB) Viewed 139 times" />
Even though some feed readers seem to be able to deal with such relative links correctly, it still looks to me as if the URLs both in the a and img tags should be absolute, not relative?
(The feed also uses the xml:base attribute, but if I understand this correctly, this is not actually related to solving (or causing) this problem.)
The related phpBB source file is phpBB/feed/helper.php, which has this section of code:
$update_count = array();
parse_attachments($forum_id, $content, $post_attachments, $update_count);
$post_attachments = implode('<br />', $post_attachments);
$post_attachments = str_replace($this->phpbb_root_path . 'download/file.' . $this->phpEx, $this->get_board_url() . '/download/file.' . $this->phpEx, $post_attachments);
$content .= $post_attachments;
but something seems wrong here – the final statement $content .= $post_attachments; seems to indicate that this code is for "non-inline" attachments, not "inline" attachments?
(Btw., the sid=... parameter should not be there either, should it?)
Originally reported in thread https://www.phpbb.com/community/viewtopic.php?f=461&t=2324921