Bun.sh WebSocket Upgrade Issue With Http.createServer

by Alex Johnson 54 views

Introduction

Are you experiencing issues with WebSocket upgrades when using http.createServer in Bun.sh? You're not alone. This article dives deep into a specific problem encountered with Bun.sh, where WebSocket traffic fails to be properly handled by a server created with the http module. We'll explore the bug, how to reproduce it, the expected behavior, and what actually occurs. If you're struggling with WebSocket connections in your Bun.sh applications, this guide is for you. Let's get started and troubleshoot this issue together.

The WebSocket Upgrade Problem in Bun.sh

When working with real-time applications, WebSockets are essential for maintaining persistent connections between the client and server. A crucial part of establishing a WebSocket connection is the HTTP Upgrade mechanism. This process allows an existing HTTP connection to be upgraded to a WebSocket connection. However, a peculiar issue arises in Bun.sh when using the http.createServer method: the WebSocket upgrade communication doesn't work as expected. This article will explore the specifics of this problem, offering insights and potential solutions for developers encountering this hiccup.

The core of the issue lies in how Bun.sh handles the upgrade event emitted by the http.Server. In Node.js, this event provides the necessary sockets and headers to facilitate the upgrade to a WebSocket connection. However, in Bun.sh, there appears to be a discrepancy in this process, leading to failed WebSocket handshakes. This problem manifests as an inability to send the necessary response to the client's upgrade request, leaving the client hanging and the WebSocket connection unestablished. Understanding this issue is critical for developers aiming to build real-time applications with Bun.sh.

Why WebSocket Upgrades Matter

Before diving deeper into the specifics of the bug, it's essential to understand why WebSocket upgrades are crucial for modern web applications. WebSockets provide a full-duplex communication channel over a single TCP connection, allowing for real-time data transfer between the client and server. This is in stark contrast to the traditional HTTP request-response model, where the client must initiate each request. WebSocket upgrades are the mechanism by which an HTTP connection is transformed into a WebSocket connection. This process begins with the client sending an HTTP request with specific headers, signaling its desire to upgrade the connection. The server then responds with a 101 Switching Protocols status code, completing the upgrade. Without this successful upgrade, real-time communication is impossible, impacting applications like chat applications, live dashboards, and online games.

Understanding the Bug in Detail

The specific bug we're addressing here revolves around the server's inability to properly respond to the client's Upgrade request. In a typical scenario, when a client sends an HTTP request with the headers Connection: upgrade and Upgrade: websocket, the server should detect this and initiate the WebSocket handshake. This involves sending back a specific HTTP response, including the 101 Switching Protocols status code. However, in Bun.sh, this response isn't being sent correctly when using http.createServer. The server fails to transmit the necessary headers and body, leaving the client in a state of limbo, waiting for a response that never comes. This behavior deviates from the expected outcome in Node.js, where the upgrade process functions smoothly. This discrepancy can cause significant issues when porting applications from Node.js to Bun.sh, particularly those relying heavily on WebSocket communication.

Reproducing the WebSocket Upgrade Bug

To better understand the issue, let's delve into the steps required to reproduce the WebSocket upgrade bug in Bun.sh. By replicating the problem, you can gain a clearer understanding of its nature and potentially explore avenues for resolution or workarounds. We will use a simple test server written in JavaScript and curl commands to simulate client requests. This hands-on approach will help solidify your understanding of the bug and its impact.

Setting Up the Test Server

The first step in reproducing the bug is setting up a test server using the http module in JavaScript. This server will listen for incoming HTTP requests and handle the upgrade event, which is triggered when a client requests a protocol upgrade (such as to WebSocket). Here's the code for the test server:

const http = require('http');

const server = http.createServer((req, res) => {
 res.writeHead(200, { 'Content-Type': 'text/plain' });
 res.end('Normal HTTP request works\n');
});

server.on('upgrade', (req, clientSocket, head) => {
 clientSocket.write(raw_response); // Not actually sending anything
 clientSocket.end();
});

const raw_response = (
 'HTTP/1.1 418 I\'m a teapot\r\n' +
 'Content-Type: text/plain\r\n' +
 'Content-Length: 30\r\n' +
 '\r\n' +
 'Upgrade request not supported\n'
);

server.listen(3000, () => { console.log('Server listening on port 3000'); });

This server does the following:

  1. Creates an HTTP server using http.createServer.
  2. Handles normal HTTP requests with a 200 OK response.
  3. Listens for upgrade events, attempting to send a custom response (418 I'm a teapot) when an upgrade request is received.
  4. Defines a raw_response string, which represents the HTTP response that should be sent for upgrade requests.
  5. Starts the server on port 3000.

Sending Requests with Curl

With the server set up, we can now send requests to it using curl. We'll send two types of requests:

  1. A normal HTTP request to verify the server is running.
  2. An HTTP request with headers that trigger the upgrade event.

Here are the curl commands to use:

curl http://localhost:3000/ -v
curl -H "Connection: upgrade" -H "Upgrade: websocket" http://localhost:3000/ -v

The first command sends a basic HTTP request. The -v flag enables verbose output, allowing us to see the headers and response. The second command sends a request with the Connection: upgrade and Upgrade: websocket headers, which should trigger the upgrade event on the server.

Observing the Behavior

When running this setup in Bun.sh, you'll observe the following:

  • The normal HTTP request (curl http://localhost:3000/ -v) works as expected, returning a 200 OK response with the message "Normal HTTP request works”.
  • The upgrade request (`curl -H