at://

Sync

Synchronizing AT Protocol data
Pages:
Streaming dataBackfillingFeeds

Handles and DIDs

In AT, handles are resolved through DIDs, also known as Decentralized Identifiers. Currently, two different DID prefixes are supported:

  • did:web, which is based on the W3C DID standard.
  • did:plc, which is a DID method developed and implemented by Bluesky. See the did-method-plc repository for details.

When you sign up for a new account using an Atmosphere app, that app will communicate with a PDS to register a new handle for you, using its domain name (for example, *.bsky.social).

Data Repositories

A data repository is a collection of data published by a single user. Repositories are self-authenticating data structures, meaning each update is signed and can be verified by anyone.

Multiple types of identifiers are used within a data repository:

  • Decentralized IDs (DIDs) identify data repositories. They are broadly used as user IDs, but since every user has one data repository then a DID can be considered a reference to a data repository.
  • Namespaced Identifiers (NSIDs) identify the Lexicon type for groups of records within a repository.
  • Record Keys ("rkeys") identify individual records within a collection in a given repository. The format is specified by the collection Lexicon.
  • Content IDs (CIDs) identify content using a fingerprint hash. They are used throughout the repository to reference the objects (nodes) within it.

Take, for example, a single AT record:

at://did:plc:vmt7o7y6titkqzzxav247zrn/app.bsky.feed.post/3m72rq2hgss2a

This can be broken down as at://DID/NSID/rkey , or at://repository/collection/record. It has a corresponding CID of bafyreidgbehqwweghrrddfu6jgj7lyr6fwhzgazhirnszdb5lvr7iynkiy.

When making a write request to an AT API endpoint — such as when creating a new post — this full repository path will be returned as a response:

{
  "uri": "at://did:plc:u5cwb2mwiv2bfq53cjufe6yn/app.bsky.feed.post/3k4duaz5vfs2b",
  "cid": "bafyreibjifzpqj6o6wcq3hejh7y4z4z2vmiklkvykc57tw3pcbx3kxifpm"
}

This is how individual records are uniquely identified and stored within AT data repositories.

PDS

A PDS, or Personal Data Server, is a server that hosts users' individual data repositories, such as posts, followers, and profile information. The PDS handles account lifecycle features, identity management, and key resolution for hosted user accounts.

You can host your own PDS, and migrate individual accounts from one PDS to another. Refer to The AT Stack for more information.

Further Reading and Resources

There are many ways of synchronizing and streaming AT data. You can use Jetstream to stream real-time updates, or locally Backfill the data that already exists on the network.