Embedding of (large?) images as data URLs breaks campaign rendering

[wmnnd]

I just came across an email campaign that had a 1 MB+ image embedded as a data url. Trying to edit the campaign in Keila ultimately led to a timeout error. Trying to manually render the campaign with Keila.Mailings.Builder.build/2 also resulted in what appeared to be an infinite loop.

We should:

• Investigate if the error is caused by excessive body size or by the use of data URLs in general
• Catch/prevent the error and/or show an appropriate error message

[katafrakt]

That was kind of fun to debug. I've been able to reproduce it with a 60K image - it takes about 40 seconds to render it on my machine. After that, I was able to narrow the culprit down to Earmark.as_html. However, I was left puzzled, because my quick reproduction script did not show the behaviour of very slow rendering.

So I pinned Earmark and Earmark Parser versions to the ones used by Keila and indeed - the slow rendering occurred. After some more playing around, I noticed that upgrading earmark_parser from 1.4.30 to 1.4.31 fixes the issue. I'm pretty sure this is related to https://github.com/RobertDober/earmark_parser/pull/125

After upgrading earmark_parser in Keila, I can no longer reproduce the issue with very slow rendering.

[wmnnd]

Thank you for finding this bug and for fixing it with a PR! Great work! :partying_face:

[wmnnd]

I’ve released Keila 0.12.5 including only your fix in the changelog to make sure all users get to use it right away.