class RealtimeBackplaneObjectCore
Since 0.2.0

Fans one replica's broadcast out to every other connected replica.

This class holds no state. Not as a simplification — as a correctness requirement. Sockets are accepted with state.acceptWebSocket, the hibernation API, which lets the Workers runtime evict the Durable Object from memory while its connections stay open and re-run the constructor when the next message arrives. A membership Set held in a field would therefore empty itself on the first hibernation, and every test that never hibernates would still pass. state.getWebSockets() survives hibernation and is the only source of truth used here.

The payload is re-broadcast verbatim, never parsed. That costs no CPU per fan-out, makes it impossible for this object to corrupt a frame, and — since a Durable Object class is deployed by the application rather than by this package — means a future widening of RealtimeFrame needs no redeploy of the object to carry the new field.

The application owns the class; this owns the behavior:

Examples

Example 1

import { DurableObject } from 'cloudflare:workers';
import { RealtimeBackplaneObjectCore } from '@setu-ts/cloudflare-plugin';

export class RealtimeBackplaneObject extends DurableObject {
  #core = new RealtimeBackplaneObjectCore(this.ctx);

  override fetch(request: Request): Promise<Response> {
    return this.#core.fetch(request);
  }
  webSocketMessage(ws: WebSocket, message: string | ArrayBuffer): void {
    this.#core.webSocketMessage(ws, message);
  }
  webSocketClose(ws: WebSocket, code: number, reason: string, wasClean: boolean): void {
    this.#core.webSocketClose(ws, code, reason, wasClean);
  }
}

Constructors

RealtimeBackplaneObjectCore(
)
Parameters

The Durable Object's ctx

Optional seams; the defaults are the deployment path

Methods

fetch(request: Request): Promise<Response>

Answers a replica's WebSocket upgrade.

webSocketClose(
code: number,
reason: string
): void

Handles a replica disconnecting.

Nothing is tracked, so nothing needs removing — the runtime drops the socket from getWebSockets() on its own. The handler exists so the application's class can forward it without a branch, and so the close is acknowledged rather than left to the runtime's default.

Handles a socket error.

The runtime closes the socket itself, so this only prevents an unhandled rejection inside the application's class.

webSocketMessage(
message: string | ArrayBuffer
): void

Re-broadcasts one replica's message to every other connected replica.

Usage

import { RealtimeBackplaneObjectCore } from "cloudflare-plugin/src/index.ts";