Gatsby: RSS/Atom Feeds should use absolute URLs to be standards-compliant

[agentofuser]

Description

• By default, gatsby-plugin-feed uses the markdownRemark node's html field as the contents of RSS entries.
• That html field has internal links and asset references as root-relative paths.
• The W3C feed validator complains that the feed should not contain relative URL references.
• The gatsby-plugin-feed README also uses the html field unaltered.
• Gatsby docs on customizing the RSS feed also use the html field with root-relative URLs.

I found a ("hacky", as he himself describes it) workaround on Dan Abramov's blog:

https://github.com/gaearon/overreacted.io/issues/65

The workaround is based on string replacement though, which would replace false-positives such as matches within code blocks. I'm also not sure whether href and src cover every use of urls in the html spec.

Steps to reproduce

• Go to https://gatsby-starter-blog-demo.netlify.com/rss.xml
• Search for salty_egg

Expected result

• href="https://gatsby-starter-blog-demo.netlify.com/static/8058f3f26913fea3b6a89a73344fe94a/2b40c/salty_egg.jpg"
• src="https://gatsby-starter-blog-demo.netlify.com/static/8058f3f26913fea3b6a89a73344fe94a/c739e/salty_egg.jpg"

Actual result

• href="/static/8058f3f26913fea3b6a89a73344fe94a/2b40c/salty_egg.jpg"
• src="/static/8058f3f26913fea3b6a89a73344fe94a/c739e/salty_egg.jpg"

[freiksenet]

Hi!

Thanks a lot for filing this issue! I wonder if you would like to make a PR to gatsby-plugin-feed to fix that?

Thank you! :purple_heart:

[agentofuser]

@freiksenet you're welcome :) I'd love to help, yes. I will probably have time to write that PR in a week or two if waiting that long is ok.

[gatsbot[bot]]

Hiya!

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[humphreybc]

Ran into this one today. @agentofuser how did you get on with the PR?

[atuttle]

I'd be happy to take a crack at it, but I don't understand the code well enough. Can anyone lend a bit of insight to help get me started?

[eubanksmd]

Found a great blog article that describes how to replace the relative URL with absolute URL in the RSS feed while this issue gets sorted out:
https://markshust.com/2020/06/25/fixing-images-in-gatsby-rss-feeds/