Verglas JavaScript Cloudflare Workers

This package builds an ordinary Cloudflare-style Worker project into a WebAssembly component. Tenant code imports DurableObject from cloudflare:workers; it does not import a Verglas shim.

Build a project

The supported wrangler.jsonc subset is:

{
  "name": "counter",
  "main": "worker.js",
  "compatibility_date": "2025-01-01",
  "compatibility_flags": [],
  "durable_objects": {
    "bindings": [
      { "name": "COUNTER", "class_name": "Counter" }
    ]
  },
  "migrations": [
    { "tag": "v1", "new_sqlite_classes": ["Counter"] }
  ],
  "vars": { "GREETING": "hello" }
}

Unknown keys are errors. Migration entries accept tag, new_classes, and new_sqlite_classes; other migration kinds are errors. The build command is:

npm install --save-dev @verglas-org/worker-js
npx verglas-worker-build ./my-worker --out ./build [--gateway <gateway.json>]

The builder bundles the project, aliases the cloudflare:workers module, and componentizes it against the service WIT world. It writes a digest-named <sha256>.wasm artifact and a Wrangler-shaped manifest.out.json whose artifacts.worker descriptor (and artifacts.durable_object when Durable Objects are declared) names the exact digest and output directory. If the selected gateway manifest exists, it must already use those nested descriptors; the builder updates them and preserves a final newline. Retired top-level component_digest and component_dir fields are rejected.

Cloudflare authoring surface

A project uses the documented Cloudflare shape:

import { DurableObject } from "cloudflare:workers";

export class Counter extends DurableObject {
  async fetch(request) {
    const row = this.ctx.storage.sql.exec("SELECT count FROM counter").one();
    return Response.json(row);
  }
}

export default {
  async fetch(request, env, ctx) {
    const id = env.COUNTER.idFromName("global");
    return env.COUNTER.get(id).fetch(request);
  },
};

env contains vars and Durable Object namespace bindings. A namespace implements idFromName, idFromString, newUniqueId, and get. Named IDs are lowercase hexadecimal SHA-256 digests of their names. A stub's fetch method is routed through the WIT bindings.do-fetch host capability.

ctx.waitUntil(promise) is awaited before a Worker event completes. This is a known v0 divergence from Cloudflare's ability to continue work after sending a response. passThroughOnException is accepted by the context but has no pass-through host route.

Pipeline Stream bindings

The manifest accepts the exact Cloudflare-shaped binding form:

"pipelines": [
  { "binding": "STREAM", "stream": "stream-id" }
]

Unknown keys are hard errors. env.STREAM is a dedicated binding with only send(records). It requires an array whose values are JSON-serializable, encodes the array as compact UTF-8 JSON, and rejects encoded requests above 5 MiB before calling verglas:do-worker/[email protected] do-fetch. The call is (binding, stream, { method: "POST", uri: "https://verglas.internal/stream/append", headers: [["content-type", "application/json"]], body, ws: undefined }). Only a 2xx response resolves the Promise; host errors and every other status reject, with no fallback path. Structured Stream schema validation is not part of this SDK surface yet; Pipeline processing must perform that validation.

Durable Object storage and events

DurableObject receives the Cloudflare ctx and env constructor arguments. ctx.storage.get, put, delete, and list send structured-clone bytes over the WIT storage verbs. The guest does not create a KV table and does not submit canonical transaction envelopes; the sandboxed host owns event transactions, commit ordering, and durability. Missing storage capabilities fail clearly.

ctx.storage.sql.exec(query, ...bindings) sends one SQL statement to storage.sql-rows. The returned cursor has toArray(), one(), raw(), columnNames, rowsRead, and rowsWritten. Positional bindings are rendered as SQL literals before crossing WIT because the v2 SQL verb carries one statement string. SQL rows are JSON objects supplied by the host.

ctx.storage.setAlarm, getAlarm, and deleteAlarm call the alarm WIT verbs. The handler export maps alarm() to the user's Durable Object alarm method.

The guest uses StarlingMonkey's real WHATWG Request, Response, Headers, WebSocketPair, and WebSocket globals. Only request and response records with byte bodies and ordered header tuples cross WIT. A pending upgrade request is accepted by ctx.acceptWebSocket(server) and a Response with status 101 and the client WebSocket; the handler response carries the accepted WIT socket ID. Socket messages and closes are delivered as Durable Object methods.

Component imports and audit

The component imports only:

• verglas:do-worker/[email protected]
• verglas:do-worker/[email protected]
• verglas:do-worker/[email protected]

It exports the Worker fetch interface and the Durable Object handler interface. ComponentizeJS is invoked with --disable=all; the build requests no WASI imports. The storage adapter is a sandboxed guest adapter and crosses only the declared WIT imports.

Local checks

pnpm install
pnpm --dir packages/worker-js test
npx verglas-worker-build examples/do-workers/js-counter --out /tmp/js-build

The tests cover the SHA-256 namespace IDs, structured-clone storage, SQL cursors, alarms, concurrency and waitUntil, HTTP boundary conversions, strict Wrangler manifest parsing, digest/gateway synchronization, component WIT conformance, and the no-WASI import audit.