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 server.stop();

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

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

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