iii-stream

The iii-stream worker stores real-time data as a three-level hierarchy (stream_name -> group_id -> item_id) in the configured adapter and exposes two surfaces: a CRUD-shaped stream::* function namespace for reading and writing items, and reactive trigger types (stream, stream:join, stream:leave) that fire on data changes and on WebSocket subscriber connect/disconnect. Reactive backends are built by binding handlers to those triggers rather than by polling.

A write persists the new value, dispatches matching stream triggers on a spawned task (fire-and-forget, so the originating call returns before handlers finish), and broadcasts the change to every WebSocket client subscribed to that (stream_name, group_id). The stream:join trigger doubles as an authorization gate: returning { unauthorized: true } from its handler rejects the subscription before any data flows. Pair it with the worker's auth_function config, which runs once per WebSocket handshake and stamps a context value into every join/leave event.

Adapters: kv (default; in-memory or file-backed; single-instance only, no cross-process fan-out) or redis (required for multi-instance fleets that need real-time fan-out). Browser and client subscriptions use the Browser SDK (iii-browser-sdk), which subscribes to stream changes over a single engine WebSocket. Connecting directly to the stream port (ws://host:{port}/stream/{stream_name}/{group_id}) is deprecated in favor of the Browser SDK.

When to Use

• A stream change should kick off side effects elsewhere (derived projections, audit logs, notifications) without polling stream::list.
• You need to gate WebSocket subscriptions server-side instead of trusting client-side filtering.
• You want server-side reactions to subscriber connect/disconnect for presence counters, per-subscription rate buckets, or audit trails.
• An item needs atomic partial updates that concurrent writers would otherwise race on.

Boundaries

• Not a general key/value store — data is stream-shaped (stream_name/group_id/item_id). Use iii-state for scope/key values.
• The default kv adapter does not fan out across processes; multi-instance fleets that need real-time broadcast must use redis.
• stream:leave is not an authorization gate — the subscription is already gone by the time it fires, and its return value is ignored.
• Trigger handlers run after the originating write returns; a handler failure neither rolls back the write nor surfaces to the caller.

Functions

• stream::set — persist an item and broadcast a create/update event; returns the previous value alongside the new one.
• stream::update — atomically apply ordered set/merge/increment/decrement/append/remove ops to an existing item.
• stream::delete — remove an item and broadcast a delete event carrying the removed value.
• stream::send — broadcast a transient event to a group's subscribers without persisting it (typing indicators, cursor positions).
• stream::get — read one item by its full (stream, group, item) triple.
• stream::list — enumerate items in a group.
• stream::list_groups — enumerate groups in a stream.
• stream::list_all — enumerate every stream's metadata.

Reactive triggers

Bind a stream-family trigger when a function should run automatically on stream activity — without polling stream::list. Three types cover two concerns: stream reacts to data changes, while stream:join / stream:leave react to WebSocket subscriber lifecycle.

Reach for them when:

• A set/update/delete/send should drive a projection, audit log, or downstream notification.
• Subscriptions need server-side authorization (stream:join) or paired setup/teardown (stream:join + stream:leave).

If you only need the current value on demand, call stream::get instead of binding a trigger.

How to bind

1. Register a handler: iii.registerFunction('presence::on-change', handler).
2. Register the trigger:

typescript
iii.registerTrigger({
  type: 'stream',
  function_id: 'presence::on-change',
  config: {
    stream_name: 'presence',  // required for `stream`; the worker indexes triggers by it.
    group_id: 'room-1',       // optional. Empty/omitted = match every group.
    item_id: 'user-123',      // optional. Empty/omitted = match every item.
    // condition_function_id is also supported.
  },
})

stream requires a non-empty stream_name; group_id / item_id use empty-as-wildcard, exact-match-otherwise semantics. stream:join and stream:leave take no config fields — branch inside the handler on the event. A stream:join handler returning { unauthorized: true } rejects the subscription; any other return allows it. Mutations that fire stream: stream::set, stream::update, stream::delete, stream::send. Reads do not.

For the event payload shape, call iii get function info on the trigger type or handler function id.