Where it's at://

Summary

You might have heard about the AT protocol (if not, read this!) Together, all servers speaking the AT protocol comprise the atmosphere—a web of hyperlinked JSON. Each piece of JSON on the atmosphere has its own at:// URI: But where do they point, exactly? Given an at:// URI, how do you locate the corresponding JSON? In this post, I’ll show you the exact process of resolving an at:// URI step by step. Turns out, this is also a great way to learn the details of how at:// works. Let’s start with the structure of a URI itself. As you might know, a URI often contains a scheme (for example, https://), an authority (like wikipedia.com), a path (like /Main_Page), and maybe a query. In most protocols, including https://, the authority part points at whoever’s hosting the data. Whoever created this data is either not present, or is in the path: https:///profile//post/3lzy2ji4nms2zbsky.appruuuuu.dethe appthe user The at:// protocol flips that around. In at:// URIs, whoever created the data is the authority, in the most literal sense: the formatthe user.feed.post/3lzy2ji4nms2zat:///app.bskyruuuuu.de The user is the authority for their own data. Whoever’s hosting the data could change over time, and is not directly included in an at:// URI. To find out the actual physical server hosting that JSON, you’re gonna need to take a few steps. Let’s try to resolve this at:// URI to the piece of JSON it represents: the formatthe user.feed.post/3lzy2ji4nms2zat:///app.bskyruuuuu.de An easy way to resolve an at:// URI is to use an SDK or a client app. Let’s try an online client, for example, pdsls or Taproot or atproto-browser. They’ll figure out the physical server where its JSON is currently hosted, and show that JSON for you. The above at:// URI points at this JSON, wherever it is currently being hosted: { "uri": "at://did:web:iam.ruuuuu.de/app.bsky.feed.post/3lzy2ji4nms2z", "cid": "bafyreiae4ehmkk4rtajs5ncagjhrsv6rj3v6fggphlbpyfco4dzddp42nu", "value": { "text": "posting from did:web, li...