[Feature] Override user-agent per domain

[kroese]

Requirements

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Is your proposal related to a problem?

A lot of newspaper websites show a cookie-wall, which prevents the OpenGraph metadata from being fetched in the link previews.

After contacting some of them, they told me to just use the GoogleBot user-agent for fetching metadata in forum software. (A bit strange advice for a large company, but this was their official solution).

So after modifying the Lemmy source to identify as Google for scraping metadata, things worked fine for those newspapers.

But I noticed for a couple of other websites, it stopped working. For example links to lemmy.world show a Cloudflare error when using GoogleBot, probably because of some bot protection mechanism. And other websites stopped working because they present a different page to Google without any metadata.

So unfortunelately switching to GoogleBot only fixes the issue on some domains, and creates an issue on others.

Describe the solution you'd like.

It would be really nice to have some file or setting, where you can specify a list of domains that need GoogleBot (or maybe specify a different user-agent per domain), and use the default user-agent Lemmy v0.19.4 for all other domains.

Describe alternatives you've considered.

There is no alternative

Additional context

No response

[Nutomic]

This sounds like a very specific use case which would be rather complicated to implement. Maybe best to do it via an extension.

[kroese]

The actual change is just a single line of code in my fork. To make it configurable is the part that it makes it difficult to implement.

So maybe its better to just have a fixed list in the code with domains that dont work without GoogleBot, as that would be much simpler.

A good side-effect could be that when people find domains that dont work with Lemmy, they are forced to do a pull-request to extend the global list, instead of just adding them to their local list. This way other instances will benefit from it too.

[dessalines]

We could just add an optional custom_metadata_fetcher_user_agent to the config hjson. We could go as complicated as per domain, but I doubt that's necessary, as long as we limit it to metadata fetching only.

[kroese]

@dessalines As described earlier, that won't work. Some domains need GoogleBot, otherwise you are redirected to their cookie-wall, and other domains refuse requests from GoogleBot (like the lemmy.world Cloudflare protection who denies the request for example).

So a single user-agent for metadata fetching will not work. Thats why we need a list somewhere, and wether that one is hard-coded or configurable is not really important to me.

[dessalines]

In that case you could add a config to crates/utils/src/settings/structs.rs that looks something like:

struct DomainAndUserAgent {
  domain: Url,
  user_agent: String,
};

struct MetadataFetcherUserAgent {
  domain_and_user_agents: Vec<DomainAndUserAgent>,
};

[dullbananas]

If requests are attempted with both user agents, would it be possible to automatically determine which response to use?

[kroese]

@dullbananas Yes.. By checking if the response contains OpenGraph tags or not.