@slothfulchat/core-wasm

chatmail core compiled to WebAssembly, exposed through the standard @deltachat/jsonrpc-client TypeScript API. Core runs in a Web Worker; the page talks to it over a yerpc transport bridging postMessage — the exact seam where deltachat-desktop's browser edition uses a WebSocket.

import { startCore } from '@slothfulchat/core-wasm'

const core = startCore()
const { dc, transport } = core
await dc.rpc.getSystemInfo()          // typed, generated from core
await transport.request('get_system_info') // raw JSON-RPC
dc.on('event', ({ contextId, event }) => ...) // core events

Hosted demo: https://web.slothful.chat/demo/ — the same page the example script below serves locally. Pass ?proxy=ws://localhost:8641 to enable networking (instructions on the page).

startCore() also returns an fs side channel into core's in-memory filesystem (blob display, temp files, backup import/export):

await core.fsWrite('/tmp/a/b.bin', new Uint8Array([1, 2, 3])) // creates parent dirs
await core.fsExists('/tmp/a/b.bin') // -> true
await core.fsRead('/tmp/a/b.bin')   // -> Uint8Array, rejects if missing
await core.fsRemove('/tmp/a/b.bin') // file or directory tree

Build (from repo root)

pnpm apply-patches                                # patched core in build/core
cd build/core/deltachat-jsonrpc/typescript
pnpm install --ignore-workspace && cargo test -p deltachat-jsonrpc \
  && node scripts/generate-constants.js && ./node_modules/.bin/tsc \
  && ./node_modules/.bin/esbuild --format=esm --bundle dist/deltachat.js --outfile=dist/deltachat.bundle.js
cd -                                              # generated TS client at the pinned commit
pnpm install
pnpm --filter @slothfulchat/core-wasm build:wasm  # needs clang + wasm32 target, ~10 min release
pnpm --filter @slothfulchat/core-wasm build
pnpm smoke                                        # headless verification
pnpm --filter @slothfulchat/core-wasm example     # http://localhost:8642/example/index.html

Networking & persistence

• IMAP/SMTP/DNS tunnel through a WebSocket→TCP bridge: run @slothfulchat/ws-tcp-proxy and pass startCore({ wsProxyUrl: 'ws://localhost:8641' }). TLS terminates inside the wasm core — the bridge only ever relays ciphertext. Without a bridge, networking errors at runtime (everything else works).
• Storage (accounts, messages, blobs) persists in OPFS by default and survives reloads; pass persist: false for a fresh in-memory core.

Current limits

• Core's HTTP goes through the browser's fetch(), so requests are subject to CORS: endpoints without permissive CORS headers fail (some provider autoconfig/OAuth2 servers); ones with them work (e.g. the webxdc apps list). Push notifications don't work.
• One tab at a time: with persistence on, the core holds an exclusive lock on its OPFS storage, so a second tab of the same app fails to start its core until the first is closed.
• No sqlcipher; webxdc and iroh are descoped.
• Always use release wasm builds; dev-profile wasm crashes the tab.