We don't often discuss Signal here at AP, not out of any sort of distaste, but because it adds new features and improvements at a slower pace than WhatsApp or Telegram. But if you happen to use Signal, then the new version has link previews in store for you. It's limited to four websites for now, but it's a good start.
According to Signal, the reason that only Imgur, Reddit, Instagram, and YouTube are supported is because those are four of the most popular websites and all of them share a focus on visual media. Further on, Signal discusses how it accomplishes this process while maintaining the security that it's known for, which you can read about below.
- The Signal app establishes a TCP connection through a privacy-enhancing proxy that obscures IP addresses from the site that is being previewed.
- A TLS session is negotiated directly between the app and the previewed site through the proxy to ensure that the Signal service never has access to the URL. Previews are not generated for non-HTTPS links.
- The Signal app retrieves preview images using overlapping range requests so that the proxy service only sees repeated requests for a fixed block size when media is transferred.
The goal behind these link previews is to expose the relevant pieces of the URL to the recipient. Some sites like us have a portion of the URL that contains relevant info, but then you have something like YouTube where it's a random string of letters, numbers, and symbols. In the latter case, you have no idea where that link goes, which is why link previews are so awesome. And in keeping with the overall theme of privacy, you can disable this feature, either permanently by visiting the settings or for just one time by tapping the 'X' in the corner of the preview before you hit send.
While a seemingly small thing, link previews are something I adore in Telegram. Signal intends to add support for more sites as soon as it's able, so be looking for those.