@effectstream/event-client

MQTT-based event subscriber for EffectStream. Subscribe to type-safe events streamed by the engine and the batcher - blocks, transactions, primitive events, and any app-defined event - without writing raw MQTT topic strings.

• MQTT subscriber for Effectstream events: blocks, transactions, primitives, app-defined.
• Type-safe topics; no raw topic strings.
• Connects to the broker run by @effectstream/event-server (or any MQTT broker).
• Bun caveat: the mqtt WebSocket transport isn't supported on Bun yet; use Node for programmatic consumption.

Install

bun add @effectstream/event-client
# or
npm install @effectstream/event-client

Standalone usage

You need a reachable MQTT broker. EffectStream's engine and batcher run brokers (default ports 8883 and 8884 over WebSocket); point at one of those, or your own.

import {
  BuiltinEvents,
  EventManager,
} from "@effectstream/event-client";

const sub = await EventManager.Instance.subscribe(
  {
    topic: BuiltinEvents.RollupBlock,
    filter: {},        // no path variables on this topic
  },
  ({ rollup, msTimestamp }) => {
    console.log("new rollup block", rollup, "at", msTimestamp);
  },
);

// Later: EventManager.Instance.unsubscribe(sub);

subscribe returns a symbol you can pass to unsubscribe. For events that encode variables in the topic path (e.g. block/${blockHeight}), pass filter: { blockHeight } to subscribe only to a specific value, or filter: { blockHeight: "*" } to subscribe to all.

Inside EffectStream

The client half of the engine/batcher event system. The engine publishes block, transaction, and primitive events to its MQTT broker; the batcher publishes its own lifecycle events. Frontends and tools (like @effectstream/wallets, the explorer, and the batcher itself) subscribe through this package; the runtime publishes via the matching @effectstream/event-server.

The most-imported symbols from this package are EventManager and BuiltinEvents. (getEvmEvent, often paired with these in state-machine primitives, lives in @effectstream/config - not here.)

Bun caveat: the mqtt package's WebSocket transport isn't supported on Bun yet. Use Node (or a TCP MQTT broker) when consuming events programmatically; the engine's exposed WebSocket transport is for browsers.

Key exports

Heavily used across the repo:

• EventManager - singleton with .subscribe, .subscribeExplicit, .unsubscribe, .sendMessage, .sendMessageExplicit. Use EventManager.Instance.
• BuiltinEvents - pre-baked typed event definitions for RollupBlock, SyncChains, batcher BatcherHash, etc. Pass these into EventManager.Instance.subscribe(...).
• toSignature(event) - "name(type1,type2,...)" string for a typed event.

Types you'll see in callback signatures: CallbackArgs<E>, CallbackAndMetadata<E>, EventPathAndDef, LogEvent, RegisteredEvent.

Also exported: EventConnect, EventBrokerNames, TopicPrefix, registerEvents, groupEvents, encodeEventForStf, toSignatureHash.

Examples

Runnable: test/examples.test.ts.

Links

• Docs: https://effectstream.github.io/docs/packages/sdk/event-client
• Source: https://github.com/effectstream/effectstream/tree/main/packages/effectstream-sdk/events