65 lines
2 KiB
TypeScript
65 lines
2 KiB
TypeScript
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import * as Y from "yjs";
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import { clog } from "./debug";
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/**
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* Minimal BroadcastChannel sync provider for a Y.Doc (features/yjs-bridge/0001 §6,
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* PoC transport — two same-origin tabs share one doc, zero backend). Encodes Yjs
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* updates and ferries them between tabs; on join it requests the current state so a
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* late tab catches up.
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*
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* Remote updates are applied with origin "remote" so (a) the reconciler treats them
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* as peer changes (its own writes use a different origin) and (b) we don't re-broadcast
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* them into a loop.
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*/
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export interface Transport {
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destroy(): void;
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}
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type Msg =
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| { t: "update"; u: Uint8Array }
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| { t: "query" }
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| { t: "state"; u: Uint8Array };
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export const REMOTE_ORIGIN = "remote";
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export function connectBroadcastChannel(
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doc: Y.Doc,
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channelName: string,
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): Transport {
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const bc = new BroadcastChannel(channelName);
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clog("BroadcastChannel open:", channelName);
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const onUpdate = (update: Uint8Array, origin: unknown) => {
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if (origin === REMOTE_ORIGIN) return; // don't echo applied remote updates
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clog("→ BC send update", update.byteLength, "bytes (origin:", String(origin) + ")");
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bc.postMessage({ t: "update", u: update } satisfies Msg);
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};
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doc.on("update", onUpdate);
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bc.onmessage = (e: MessageEvent<Msg>) => {
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const msg = e.data;
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if (!msg) return;
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switch (msg.t) {
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case "update":
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case "state":
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clog("← BC recv", msg.t, msg.u?.byteLength, "bytes → applyUpdate");
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Y.applyUpdate(doc, new Uint8Array(msg.u), REMOTE_ORIGIN);
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break;
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case "query":
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clog("← BC recv query → replying with state");
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bc.postMessage({ t: "state", u: Y.encodeStateAsUpdate(doc) } satisfies Msg);
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break;
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}
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};
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// Ask any existing tab for the current state.
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clog("→ BC send query (asking peers for state)");
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bc.postMessage({ t: "query" } satisfies Msg);
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return {
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destroy: () => {
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doc.off("update", onUpdate);
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bc.close();
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},
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};
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}
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