Bun HTTP Server

Bun has a built-in high-performance HTTP server via Bun.serve().

Quick Start

const server = Bun.serve({
  port: 3000,
  fetch(req) {
    return new Response("Hello World!");
  },
});

console.log(`Server running at http://localhost:${server.port}`);

Request Handling

Bun.serve({
  fetch(req) {
    const url = new URL(req.url);

    // Method
    console.log(req.method); // GET, POST, etc.

    // Path
    console.log(url.pathname); // /api/users

    // Query params
    console.log(url.searchParams.get("id")); // ?id=123

    // Headers
    console.log(req.headers.get("Content-Type"));

    return new Response("OK");
  },
});

Body Parsing

Bun.serve({
  async fetch(req) {
    // JSON
    const json = await req.json();

    // Form data
    const form = await req.formData();

    // Text
    const text = await req.text();

    // ArrayBuffer
    const buffer = await req.arrayBuffer();

    // Blob
    const blob = await req.blob();

    return new Response("Received");
  },
});

Response Types

Bun.serve({
  fetch(req) {
    const url = new URL(req.url);

    switch (url.pathname) {
      case "/json":
        return Response.json({ message: "Hello" });

      case "/html":
        return new Response("<h1>Hello</h1>", {
          headers: { "Content-Type": "text/html" },
        });

      case "/redirect":
        return Response.redirect("/new-location", 302);

      case "/file":
        return new Response(Bun.file("./image.png"));

      case "/stream":
        return new Response(
          new ReadableStream({
            start(controller) {
              controller.enqueue("chunk1");
              controller.enqueue("chunk2");
              controller.close();
            },
          })
        );

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

Simple Routing

Bun.serve({
  fetch(req) {
    const url = new URL(req.url);
    const path = url.pathname;
    const method = req.method;

    // Static routes
    if (method === "GET" && path === "/") {
      return new Response("Home");
    }

    if (method === "GET" && path === "/api/users") {
      return Response.json([{ id: 1, name: "Alice" }]);
    }

    // Dynamic routes
    const userMatch = path.match(/^\/api\/users\/(\d+)$/);
    if (method === "GET" && userMatch) {
      const userId = userMatch[1];
      return Response.json({ id: userId });
    }

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

Error Handling

Bun.serve({
  fetch(req) {
    try {
      // Handle request
      throw new Error("Something went wrong");
    } catch (error) {
      return new Response(
        JSON.stringify({ error: error.message }),
        {
          status: 500,
          headers: { "Content-Type": "application/json" }
        }
      );
    }
  },
  error(error) {
    // Global error handler
    return new Response(`Error: ${error.message}`, { status: 500 });
  },
});

Server Options

const server = Bun.serve({
  port: 3000,           // Default: 3000
  hostname: "0.0.0.0",  // Default: "0.0.0.0"

  development: true,    // Pretty errors in browser

  // TLS/HTTPS
  tls: {
    key: Bun.file("./key.pem"),
    cert: Bun.file("./cert.pem"),
  },

  // Unix socket
  unix: "/tmp/my-socket.sock",

  // Max request body size (default 128MB)
  maxRequestBodySize: 1024 * 1024 * 10, // 10MB

  fetch(req) {
    return new Response("OK");
  },
});

Server Methods

const server = Bun.serve({ ... });

// Server info
console.log(server.port);        // 3000
console.log(server.hostname);    // "0.0.0.0"
console.log(server.url);         // URL object

// Stop server (Bun 1.2+: returns a Promise — await it to flush in-flight
// requests; calling it without await may not drain connections).
await server.stop();

// Reload with new config
server.reload({
  fetch(req) {
    return new Response("Updated!");
  },
});

// Pending requests count
console.log(server.pendingRequests);

Routing with routes (Bun 1.2+)

The examples above use the classic fetch(req) handler with manual URL parsing, which still works. As of Bun 1.2, the canonical way to declare route maps is the routes option, with dynamic params available on req.params:

Bun.serve({
  routes: {
    "/api/users": {
      GET: () => Response.json([{ id: 1, name: "Alice" }]),
      POST: async (req) => Response.json(await req.json(), { status: 201 }),
    },
    "/api/users/:id": (req) => {
      const { id } = req.params;
      return Response.json({ id });
    },
  },
  fetch(req) {
    return new Response("Not Found", { status: 404 });
  },
});

Use routes for new code; keep fetch as a fallback for unmatched paths.

Static Files

Bun.serve({
  fetch(req) {
    const url = new URL(req.url);

    // Serve static files from public/
    if (url.pathname.startsWith("/static/")) {
      const filePath = `./public${url.pathname.replace("/static", "")}`;
      const file = Bun.file(filePath);

      if (await file.exists()) {
        return new Response(file);
      }
      return new Response("Not Found", { status: 404 });
    }

    return new Response("API");
  },
});

CORS

function corsHeaders() {
  return {
    "Access-Control-Allow-Origin": "*",
    "Access-Control-Allow-Methods": "GET, POST, PUT, DELETE, OPTIONS",
    "Access-Control-Allow-Headers": "Content-Type, Authorization",
  };
}

Bun.serve({
  fetch(req) {
    // Handle preflight
    if (req.method === "OPTIONS") {
      return new Response(null, { headers: corsHeaders() });
    }

    // Add CORS headers to response
    return new Response("OK", { headers: corsHeaders() });
  },
});

Common Errors

Error	Cause	Fix
EADDRINUSE	Port in use	Use different port or kill process
Cannot read body	Body already consumed	Read body once only
CORS error	Missing headers	Add CORS headers
413 Payload Too Large	Body exceeds limit	Increase maxRequestBodySize

When to Load References

Load references/tls-config.md when:

• HTTPS/TLS setup
• Certificate configuration
• mTLS authentication

Load references/streaming.md when:

• Server-sent events
• Streaming responses
• Chunked transfer encoding