Discord still uses the wrong user-agent when fetching image previews

[xPaw]

The issue was locked, but the issue persists: #1600

At some point the user-agent was upgraded to "Mozilla/5.0 (Macintosh; Intel Mac OS X 11.6; rv:92.0) Gecko/20100101 Firefox/92.0"

Cloudflare shows requests with agent "Mozilla/5.0 (compatible; Discordbot/2.0; +https://discordapp.com)" as a verified bot, but not the Firefox agent used by image fetches. As a result when using bot management, link embed will be fetched, but the image will not be.

As I mentioned in the locked issue, other bots and applications that I am aware uses a clearly identifiable user-agent when requesting metadata and images. This is an odd discrepancy that Discord does.

[devsnek]

The original reasoning given in the linked issue is still correct:

This is an intentional design decision, and is working as intended. When Discord crawls a URL we perform that action as a bot. However, when we proxy images we are acting in response to a user loading that image. Because of this distinction we provide a user agent of a user, not a bot.

[xPaw]

But why? Can you elaborate what problem this solves?

I also don't think the proxying statement is correct when the thumbnail image is missing from the link preview entirely.

Using embed debugger, it says "Unable to extract thumbnail: Internal error", and there is no thumbnail url in the embed json at all, implying the attempt to fetch the image was made during link crawl, and not when user tries to proxy it from the link embed.

If this statement was true, I would see an image failing to load in Discord for link previews, but there's just no thumbnail at all.

[ishields]

@xPaw have you found a solution to this? I'm running into the same issue and the image thumbnails from cloudflare do not load even though they are valid image URLs that I can load fine on a website or by going directly to them in chrome.

[SkyLeite]

I imagine the "problem" this solves is that people can't reasonably make links that show a different image when shown on Discord. Of course this is a clear abuse of the User-Agent system by Discord, and they know it's an indefensible position since they just lock every discussion related to it.

[xPaw]

Seems like this was fixed at some point? I just tested it, and the image was fetched with "Mozilla/5.0 (compatible; Discordbot/2.0; +https://discordapp.com)" agent, but for some reason it fetched the image 3 times.