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[Bug report] Lemmy CA rich link previews for some posts show the captcha challenge, not actual content (self.lemmy_ca_support)

submitted 1 week ago by CrashLoopBackOff to c/lemmy_ca_support

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Link posts from thetyee.ca appear to be previewing the Cloudflare captcha challenge "Attention Required! | Cloudflare" prompt instead of actual content.

What it looks like (two examples - this seems to be a consistent problem for thetyee):

(from https://lemmy.ca/post/39053782)

(from https://lemmy.ca/post/39058782)

What it should look like (a different post):

My guess is that the rich link preview is generated in Lemmy's backend, and Cloudflare thinks that the IP address of lemmy.ca's host is full of bots.

No educated guess on the solution, though, but I'd guess that other Lemmy admins have seen sort of thing too.

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[–] Shadow 6 points 1 week ago* (last edited 1 week ago) (1 children)

Huh, weird..... I don't think this is solvable on our side, this is thetyee's cloudflare rules blocking us.

[–] avidamoeba 3 points 1 week ago (2 children)

Is there a config option to make the preview generation on the client side?

[–] [email protected] 3 points 1 week ago (1 children)

Can't you make a text post, generate your own preview by downloading the pic, put a link to the article, copy the headline into the title and upload your preview?

[–] avidamoeba 2 points 1 week ago* (last edited 1 week ago)

That's basically what I do for CBC articles because they don't generate a preview for some reason. You could plausibly automate this in JS on the client side. Could even be a separate, user control where the user has to click a button for the functionality to trigger. Could be implemented in an alt client too. There are options, they just need work. :D

[–] Shadow 3 points 1 week ago (1 children)

Unfortunately not

[–] avidamoeba 3 points 1 week ago* (last edited 1 week ago) (2 children)

That means we'd keep running into stuff like this long term as the server/s IP/s get flagged by various CDNs and what not. Oh well. Not much we can do unless one of us gets the work done and shepherds a PR into Lemmy mainline.

[–] Shadow 3 points 1 week ago (1 children)

I think that might introduce concerns around a client presenting modified info vs what everyone else would see. I'd imagine Facebook / discord and everyone else that generates link previews, struggle with this problem.

[–] avidamoeba 2 points 1 week ago* (last edited 1 week ago)

Yes but people can put whatever info in the title, thumbnail, etc. so I imagine the previews are more about convenience than accuracy. I think accuracy is handled by the voting system first and moderation second. There are likely corner cases I'm not considering so yes, there likely would be concerns about that either way. I'm just thinking about it from a low-cost compromise perspective.

Yeah for sure they do and they have large pools of IPs that cost money we probably don't want to spend. They also likely can directly talk to CDNs and IP list providers to allowlist their IPs. :D I used to work for a bit at the VPN side of a security company and the struggle for clean IPs was real. AWS solved that but it was very expensive compared to metal in smaller DCs.

[–] CrashLoopBackOff 1 points 1 week ago

Lemmy mainline could also skip rich link preview generation if it returns a non-2xx status. Have a few retries if link preview generation fails, and omit the preview entirely if retries are exhausted. I think the Attention Required! | Cloudflare prompt is associated with a 403 Forbidden status code.

And also generate some logs of what addresses are being refused, so the Lemmy admins can reach out to the content owners and get their servers unblocked, maybe.

[–] Rentlar 1 points 1 week ago

The preview generator is an "automated" visit of the page so the site tends to reject it.

Usually, OPs put a short summary of their own in the post body text, plus their thoughts in a top-level comment.