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Skyfall

A Ruby gem for streaming data from the Bluesky/AtProto firehose 🦋

Note

ATProto Ruby gems collection: skyfall | blue_factory | minisky | didkit

What does it do

Skyfall is a Ruby library for connecting to the "firehose" of the Bluesky social network, i.e. a websocket which streams all new posts and everything else happening on the Bluesky network in real time. The code connects to the websocket endpoint, decodes the messages which are encoded in some binary formats like DAG-CBOR, and returns the data as Ruby objects, which you can filter and save to some kind of database (e.g. in order to create a custom feed).

Installation

gem install skyfall

Usage

Start a connection to the firehose by creating a Skyfall::Stream object, passing the server hostname and endpoint name:

require 'skyfall'

sky = Skyfall::Stream.new('bsky.network', :subscribe_repos)

Add event listeners to handle incoming messages and get notified of errors:

sky.on_connect { puts "Connected" }
sky.on_disconnect { puts "Disconnected" }

sky.on_message { |m| p m }
sky.on_error { |e| puts "ERROR: #{e}" }

When you're ready, open the connection by calling connect:

sky.connect

Processing messages

Each message passed to on_message is an instance of a subclass of WebsocketMessage, depending on the message type. The supported message types are:

  • CommitMessage (#commit) - represents a change in a user's repo; most messages are of this type
  • HandleMessage (#handle) - when a different handle is assigned to a user's DID
  • TombstoneMessage (#tombstone) - when an account is deleted
  • InfoMessage (#info) - a protocol error message, e.g. about an invalid cursor parameter
  • UnknownMessage is used for other unrecognized message types

All message objects have the following properties:

  • type (symbol) - the message type identifier, e.g. :commit
  • seq (integer) - a sequential index of the message
  • repo or did (string) - DID of the repository (user account)
  • time (Time) - timestamp of the described action

All properties except type may be nil for some message types that aren't related to a specific user, like #info.

Commit messages additionally have:

  • commit - CID of the commit
  • prev - CID of the previous commit in that repo
  • operations - list of operations (usually one)

Handle messages additionally have:

  • handle - the new handle assigned to the DID

Info messages additionally have:

  • name - identifier of the message/error
  • message - a human-readable description

Commit operations

Operations are objects of type Operation and have such properties:

  • repo or did (string) - DID of the repository (user account)
  • collection (string) - name of the relevant collection in the repository, e.g. app.bsky.feed.post for posts
  • type (symbol) - short name of the collection, e.g. :bsky_post
  • rkey (string) - identifier of a record in a collection
  • path (string) - the path part of the at:// URI - collection name + ID (rkey) of the item
  • uri (string) - the complete at:// URI
  • action (symbol) - :create, :update or :delete
  • cid - CID of the operation/record (nil for delete operations)

Create and update operations will also have an attached record (JSON object) with details of the post, like etc. The record data is currently available as a Ruby hash via raw_record property (custom types will be added in future).

So for example, in order to filter only "create post" operations and print their details, you can do something like this:

sky.on_message do |m|
  next if m.type != :commit

  m.operations.each do |op|
    next unless op.action == :create && op.type == :bsky_post

    puts "#{op.repo}:"
    puts op.raw_record['text']
    puts
  end
end

For more examples, see the example folder or the bluesky-feeds-rb project, which implements a feed generator service.

Custom lexicons

A note on custom lexicons: the Skyfall::Operation objects have two properties that tell you the kind of record they're about: #collection, which is a string containing the official name of the collection/lexicon, e.g. "app.bsky.feed.post"; and #type, which is a symbol meant to save you some typing, e.g. :bsky_post.

When Skyfall receives a message about a record type that's not on the list, whether in the app.bsky namespace or not, the operation type will be :unknown, while the collection will be the original string. So if an app like e.g. "Skygram" appears with a zz.skygram.* namespace that lets you share photos on ATProto, the operations will have a type :unknown and collection names like zz.skygram.feed.photo, and you can check the collection field for record types known to you and process them in some appropriate way, even if Skyfall doesn't recognize the record type.

Do not however check if such operations have a type equal to :unknown first - just ignore the type and only check the collection string. The reason is that some next version of Skyfall might start recognizing those records and add a new type value for them like e.g. :skygram_photo, and then they won't match your condition anymore.

Configuration

User agent

Skyfall::Stream sends a user agent header when making a connection. This is set by default to "Skyfall/0.x.y", but it's recommended that you override it using the user_agent field to something that identifies your app and its author – this will let the owner of the server you're connecting to know who to contact in case the client is causing some problems.

You can also append your user agent info to the default value like this:

sky.user_agent = "NewsBot (@news.bot) #{sky.default_user_agent}"

Heartbeat and reconnecting

Occasionally, especially during times of very heavy traffic, the websocket can get into a stuck state where it stops receiving any data, but doesn't disconnect and just hangs like this forever. To work around this, there is a "heartbeat" feature which starts a background timer, which periodically checks how much time has passed since the last received event, and if the time exceeds a set limit, it manually disconnects and reconnects the stream.

The option is not enabled by default, because there are some firehoses which will not be sending events often, possibly only once in a while – e.g. labellers and independent PDS firehoses – and in this case we don't want any heartbeat since it will be completely normal not to have any events for a long time. It's not really possible to detect easily if we're connecting to a full network relay or one of those, so in order to avoid false alarms, you need to enable this manually using the check_heartbeat property.

You can also change the heartbeat_interval, i.e. how often the timer is triggered (default: 10s), and the heartbeat_timeout, i.e. the amount of time passed without events when it reconnects (default: 5 min):

sky.check_heartbeat = true
sky.heartbeat_interval = 5
sky.heartbeat_timeout = 120

Credits

Copyright © 2024 Kuba Suder (@mackuba.eu).

The code is available under the terms of the zlib license (permissive, similar to MIT).

Bug reports and pull requests are welcome 😎