ChatApp/apps/desktop/src/workers/crypto.worker.ts

// Web Worker — runs Argon2id pwhash + sealed user-key open off the main
// thread. PIN-unlock used to freeze the UI for ~1-2 s on mid-hardware while
// the moderate-preset KDF ran; pushing it here keeps the unlock screen
// responsive.
//
// The worker bundles its own libsodium-wrappers-sumo instance and registers
// it as the shared CryptoBackend inside this worker realm — there is no
// shared state with the main thread, so we initialise once per worker and
// re-use it across messages (the client wrapper currently spawns one-shot,
// but the worker is safe to keep alive too).
//
// Message protocol (one-shot RPC):
//   request:  { op: 'openUserKey', input: OpenUserKeyInput }
//   response: { ok: true,  result: { privateKey: Uint8Array } }
//           | { ok: false, error: string }
//
// The private key bytes are transferred (zero-copy) back to the caller via
// the structured-clone Transferable list; the worker's view of the buffer is
// detached on transfer which also clears the only worker-side reference.

/// <reference lib="webworker" />

import { setCryptoBackend, openUserKey } from '@chat-app/shared/crypto';
import type { KdfParams } from '@chat-app/shared/crypto';
import sodium from 'libsodium-wrappers-sumo';

import { createLibsodiumBackend } from '../lib/cryptoBackend';

export interface OpenUserKeyInput {
  sealed: Uint8Array;
  pin: string;
  salt: Uint8Array;
  kdfParams: KdfParams;
}

export interface OpenUserKeyResult {
  privateKey: Uint8Array;
}

type WorkerRequest = { op: 'openUserKey'; input: OpenUserKeyInput };
type WorkerResponse =
  | { ok: true; result: OpenUserKeyResult }
  | { ok: false; error: string };

let backendReady: Promise<void> | null = null;

async function ensureBackend(): Promise<void> {
  if (!backendReady) {
    backendReady = (async () => {
      await sodium.ready;
      setCryptoBackend(await createLibsodiumBackend());
    })();
  }
  return backendReady;
}

self.addEventListener('message', (ev: MessageEvent<WorkerRequest>) => {
  const msg = ev.data;
  void (async () => {
    try {
      if (!msg || msg.op !== 'openUserKey') {
        throw new Error('unknown op: ' + String((msg as { op?: unknown })?.op));
      }
      await ensureBackend();
      const privateKey = await openUserKey(msg.input);
      const response: WorkerResponse = { ok: true, result: { privateKey } };
      const transfers: Transferable[] = [];
      if (privateKey?.buffer instanceof ArrayBuffer) {
        transfers.push(privateKey.buffer);
      }
      (self as unknown as Worker).postMessage(response, transfers);
    } catch (err) {
      const message = err instanceof Error ? err.message : String(err);
      const response: WorkerResponse = { ok: false, error: message };
      (self as unknown as Worker).postMessage(response);
    }
  })();
});