[wp-trac] [WordPress Trac] #35043: Images in RSS feed are broken

[WordPress Trac]

#35043: Images in RSS feed are broken
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 Reporter:  griffinjay        |       Owner:  joemcgill
     Type:  defect (bug)      |      Status:  reviewing
 Priority:  normal            |   Milestone:  4.4.1
Component:  Media             |     Version:  4.4
 Severity:  normal            |  Resolution:
 Keywords:  has-patch commit  |     Focuses:
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Comment (by joemcgill):

 I've set up a RSS-to-Email campaign with MailChimp to test the original
 issue mentioned in this ticket and there are several interesting layers to
 keep in mind in this process.

 First of all, the [http://trialstrainingcenter.com/wp-
 content/uploads/2015/12/TTC-mailchimp-broken-images.png  MailChimp
 screenshot] posted by @griffinjay shows the email preview that is part of
 MailChimp's product web app. It looks like they're parsing all images in
 feeds and displaying them through a CloudFront proxy so they can show
 previews over a secure HTTPS connection. However, they are not proxying
 images in the `srcset` attribute, so those requests are being blocked by
 mixed content errors within the app.

 However, once the email is sent, the choice of how to display those images
 is up to the client receiving the email. Apple's mail app displays the
 original HTML, including `srcset` and `sizes` but those attributes are
 effectively ignored by the HTML parser (or so it seems). Google Inbox
 parses the HTML and rewrites `img` tags entirely so sources can be proxied
 through their own secure network. Office 365, on the other hand, currently
 strips out `srcset` and `sizes` attributes, but serves the original image
 asset over HTTP.

 In all cases I tested of RSS-to-email, the image was displayed in the
 email client without any breakage.

 However, Feedly.com, a fairly popular RSS reader, seems to be choking on
 HTTP images requested via `srcset` attributes because of mixed content
 warnings, even though HTTP images requested via `src` attributes load just
 fine. Kind of odd.

 Since responsive image markup included in feeds only seems to affect
 specific cases, I'm still inclined to leave it on by default as a way of
 encouraging third party software to take `srcset` attributes into account
 inside their apps. For anyone who needs to turn off responsive image
 support in their feeds, we have a documented workaround, which we could
 put into a standalone plugin if needed.

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Ticket URL: <https://core.trac.wordpress.org/ticket/35043#comment:12>
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