goose

A Gleam WebSocket consumer for AT Protocol Jetstream events.

gleam add goose@1

Example

import goose
import gleam/io
import gleam/option

pub fn main() {
  // Create a default configuration
  let config = goose.default_config()

  // Or configure with custom options
  let config = goose.JetstreamConfig(
    endpoint: "wss://jetstream2.us-east.bsky.network/subscribe",
    wanted_collections: ["app.bsky.feed.post", "app.bsky.feed.like"],
    wanted_dids: [],
    cursor: option.None,
    max_message_size_bytes: option.None,
    compress: False,
    require_hello: False,
  )

  // Start consuming events
  goose.start_consumer(config, fn(json_event) {
    let event = goose.parse_event(json_event)

    case event {
      goose.CommitEvent(did, time_us, commit) -> {
        io.println("Commit: " <> commit.operation <> " in " <> commit.collection)
      }
      goose.IdentityEvent(did, time_us, identity) -> {
        io.println("Identity: " <> identity.handle)
      }
      goose.AccountEvent(did, time_us, account) -> {
        io.println("Account updated: " <> did)
      }
      goose.UnknownEvent(_) -> {
        io.println("Unknown event type")
      }
    }
  })
}

Configuration Options

wanted_collections

An array of Collection NSIDs to filter which records you receive (default: empty = all collections)

• Supports NSID path prefixes like app.bsky.graph.* or app.bsky.*
• The prefix before .* must pass NSID validation
• Incomplete prefixes like app.bsky.graph.fo* are not supported
• Account and Identity events are always received regardless of this filter
• Maximum 100 collections/prefixes

Example:

wanted_collections: ["app.bsky.feed.post", "app.bsky.graph.*"]

wanted_dids

An array of Repo DIDs to filter which records you receive (default: empty = all repos)

• Maximum 10,000 DIDs

Example:

wanted_dids: ["did:plc:example123", "did:plc:example456"]

cursor

A unix microseconds timestamp to begin playback from

• Absent cursor or future timestamp results in live-tail operation
• When reconnecting, use time_us from your most recently processed event
• Consider subtracting a few seconds as a buffer to ensure gapless playback

Example:

cursor: option.Some(1234567890123456)

max_message_size_bytes

The maximum size of a payload that this client would like to receive

• Zero means no limit
• Negative values are treated as zero
• Default: 0 (no maximum size)

Example:

max_message_size_bytes: option.Some(1048576)  // 1MB limit

compress

Enable zstd compression for WebSocket frames

• Set to True to enable compression
• Default: False
• Uses zstandard compression with Jetstream’s custom dictionary
• Reduces bandwidth by approximately 50%
• Messages are automatically decompressed before reaching your callback
• Requires the ezstd library (automatically handled as a dependency)

Example:

compress: True

Note: Compression is transparent to your application - compressed messages are automatically decompressed before being passed to your event handler. The bandwidth savings occur on the wire between the server and your client.

require_hello

Pause replay/live-tail until server receives a SubscriberOptionsUpdatePayload

• Set to True to require initial handshake
• Default: False

Example:

require_hello: True

Full Configuration Example

import goose
import gleam/option

let config = goose.JetstreamConfig(
  endpoint: "wss://jetstream2.us-east.bsky.network/subscribe",
  wanted_collections: ["app.bsky.feed.post", "app.bsky.graph.*"],
  wanted_dids: ["did:plc:example123"],
  cursor: option.Some(1234567890123456),
  max_message_size_bytes: option.Some(2097152),  // 2MB
  compress: True,
  require_hello: False,
)

goose.start_consumer(config, handle_event)

Further documentation can be found at https://hexdocs.pm/goose.

Development

gleam build # Build the project
gleam test  # Run the tests