Agent Skills: Bun Cloudflare Workers

Bun Cloudflare Workers

Build and deploy Cloudflare Workers using Bun for development.

Quick Start

# Create new Workers project
bunx create-cloudflare my-worker
cd my-worker

# Install dependencies
bun install

# Development
bun run dev

# Deploy
bun run deploy

Secure Installation

Scaffolding tools like bunx create-cloudflare download and execute remote code. Before running, follow supply chain security best practices:

• Block post-install scripts — Bun disables them by default; allow specific packages via trustedDependencies in package.json
• Cooldown period — Configure minimumReleaseAge in bunfig.toml to wait 7 days for new versions
• Audit before installing — Run socket package score npm <pkg> or use socket npm install <pkg> to check packages

Load the dependency-upgrade skill for full security configuration including Socket CLI integration, cooldown setup, lockfile validation, and CI enforcement.

Project Setup

package.json

{
  "scripts": {
    "dev": "wrangler dev",
    "deploy": "wrangler deploy",
    "build": "bun build src/index.ts --outdir=dist --target=browser"
  },
  "devDependencies": {
    "@cloudflare/workers-types": "^4.20250906.0",
    "wrangler": "^4.54.0"
  }
}

wrangler.toml

name = "my-worker"
main = "src/index.ts"
compatibility_date = "2024-01-01"

# Use Bun for local dev
[dev]
local_protocol = "http"

# Bindings
[[kv_namespaces]]
binding = "KV"
id = "xxx"

[[d1_databases]]
binding = "DB"
database_name = "my-db"
database_id = "xxx"

Basic Worker

// src/index.ts
export default {
  async fetch(request: Request, env: Env, ctx: ExecutionContext): Promise<Response> {
    const url = new URL(request.url);

    if (url.pathname === "/") {
      return new Response("Hello from Cloudflare Workers!");
    }

    if (url.pathname === "/api/data") {
      return Response.json({ message: "Hello" });
    }

    return new Response("Not Found", { status: 404 });
  },
};

interface Env {
  KV: KVNamespace;
  DB: D1Database;
}

Using Hono

// src/index.ts
import { Hono } from "hono";

type Bindings = {
  KV: KVNamespace;
  DB: D1Database;
};

const app = new Hono<{ Bindings: Bindings }>();

app.get("/", (c) => c.text("Hello Hono!"));

app.get("/api/users", async (c) => {
  const users = await c.env.DB.prepare("SELECT * FROM users").all();
  return c.json(users.results);
});

app.post("/api/users", async (c) => {
  const { name } = await c.req.json();
  await c.env.DB.prepare("INSERT INTO users (name) VALUES (?)").bind(name).run();
  return c.json({ success: true });
});

export default app;

KV Storage

export default {
  async fetch(request: Request, env: Env): Promise<Response> {
    const url = new URL(request.url);
    const key = url.searchParams.get("key");

    if (request.method === "GET" && key) {
      const value = await env.KV.get(key);
      return Response.json({ key, value });
    }

    if (request.method === "PUT" && key) {
      const value = await request.text();
      await env.KV.put(key, value, { expirationTtl: 3600 });
      return Response.json({ success: true });
    }

    return new Response("Bad Request", { status: 400 });
  },
};

D1 Database

export default {
  async fetch(request: Request, env: Env): Promise<Response> {
    // Query
    const { results } = await env.DB.prepare(
      "SELECT * FROM users WHERE active = ?"
    ).bind(1).all();

    // Insert
    const info = await env.DB.prepare(
      "INSERT INTO users (name, email) VALUES (?, ?)"
    ).bind("Alice", "alice@example.com").run();

    // Transaction
    const batch = await env.DB.batch([
      env.DB.prepare("INSERT INTO users (name) VALUES (?)").bind("Bob"),
      env.DB.prepare("INSERT INTO users (name) VALUES (?)").bind("Charlie"),
    ]);

    return Response.json(results);
  },
};

Durable Objects

// src/counter.ts
export class Counter {
  private state: DurableObjectState;
  private value = 0;

  constructor(state: DurableObjectState) {
    this.state = state;
    this.state.blockConcurrencyWhile(async () => {
      this.value = (await this.state.storage.get("value")) || 0;
    });
  }

  async fetch(request: Request): Promise<Response> {
    const url = new URL(request.url);

    if (url.pathname === "/increment") {
      this.value++;
      await this.state.storage.put("value", this.value);
    }

    return Response.json({ value: this.value });
  }
}

// src/index.ts
export { Counter } from "./counter";

export default {
  async fetch(request: Request, env: Env): Promise<Response> {
    const id = env.COUNTER.idFromName("global");
    const stub = env.COUNTER.get(id);
    return stub.fetch(request);
  },
};

# wrangler.toml
[[durable_objects.bindings]]
name = "COUNTER"
class_name = "Counter"

[[migrations]]
tag = "v1"
new_classes = ["Counter"]

R2 Storage

export default {
  async fetch(request: Request, env: Env): Promise<Response> {
    const url = new URL(request.url);
    const key = url.pathname.slice(1);

    if (request.method === "GET") {
      const object = await env.BUCKET.get(key);
      if (!object) {
        return new Response("Not Found", { status: 404 });
      }
      return new Response(object.body, {
        headers: { "Content-Type": object.httpMetadata?.contentType || "application/octet-stream" },
      });
    }

    if (request.method === "PUT") {
      await env.BUCKET.put(key, request.body, {
        httpMetadata: { contentType: request.headers.get("Content-Type") || undefined },
      });
      return Response.json({ success: true });
    }

    return new Response("Method Not Allowed", { status: 405 });
  },
};

Development with Bun

Local Development

# Run with wrangler (uses Bun for TypeScript)
bun run dev

# Or directly
bunx wrangler dev

Testing with Bun

// src/index.test.ts
import { describe, test, expect } from "bun:test";

// Mock worker
const worker = {
  async fetch(request: Request) {
    return new Response("Hello");
  },
};

describe("Worker", () => {
  test("returns hello", async () => {
    const request = new Request("http://localhost/");
    const response = await worker.fetch(request);
    expect(await response.text()).toBe("Hello");
  });
});

Miniflare for Testing

import { Miniflare } from "miniflare";

const mf = new Miniflare({
  script: await Bun.file("./dist/index.js").text(),
  kvNamespaces: ["KV"],
});

const response = await mf.dispatchFetch("http://localhost/");
console.log(await response.text());

Build for Production

// build.ts
await Bun.build({
  entrypoints: ["./src/index.ts"],
  outdir: "./dist",
  target: "browser", // Workers use browser APIs
  minify: true,
  sourcemap: "external",
});

bun run build.ts
bunx wrangler deploy

Environment Variables

# wrangler.toml
[vars]
API_URL = "https://api.example.com"

# Secrets (set via CLI)
# wrangler secret put API_KEY

export default {
  async fetch(request: Request, env: Env): Promise<Response> {
    console.log(env.API_URL);    // From vars (non-secret, safe to log)
    // Access a Worker secret (NEVER log it — wrangler tail / Logpush persist logs)
    if (env.API_KEY) {
      // use env.API_KEY to call the upstream API
    }
    // ❌ NEVER: console.log(env.API_KEY) — secrets must not appear in logs
    return new Response("OK");
  },
};

Scheduled Workers (Cron)

export default {
  async scheduled(event: ScheduledEvent, env: Env, ctx: ExecutionContext): Promise<void> {
    console.log("Cron triggered at:", event.scheduledTime);
    // Perform scheduled task
    await env.DB.prepare("DELETE FROM logs WHERE created_at < ?")
      .bind(Date.now() - 7 * 24 * 60 * 60 * 1000)
      .run();
  },

  async fetch(request: Request, env: Env): Promise<Response> {
    return new Response("OK");
  },
};

# wrangler.toml
[triggers]
crons = ["0 * * * *"]  # Every hour

Common Errors

| Error | Cause | Fix | |-------|-------|-----| | Bun API not available | Workers use V8 | Use Web APIs only | | Module not found | Build issue | Check bundler config | | Script too large | Exceeds 10MB | Optimize bundle | | CPU time exceeded | Long execution | Optimize or use queues |

API Compatibility

Workers support Web APIs, NOT Bun-specific APIs:

| Available | Not Available | |-----------|---------------| | fetch() | Bun.file() | | Response | Bun.serve() | | Request | bun:sqlite | | URL | bun:ffi | | crypto | fs | | TextEncoder | child_process |

When to Load References

Load references/bindings.md when:

• Advanced KV/D1/R2 patterns
• Queue workers
• Service bindings

Load references/performance.md when:

• Bundle optimization
• Cold start reduction
• Caching strategies