Chapter 7. Debugging and Tools

Previous chapters have gone into depth on building out solutions for using WebSocket in your applications. While in the process of integrating any technology into a new or existing project, perhaps the most vital tool is learning how to debug when things don’t go as originally planned.

In this chapter you’ll explore several areas of the WebSocket lifecycle and review tools that can aid in your journey across the WebSocket landscape. Let’s take one of the previous examples for a spin, and take a look at what’s being passed around and how you can use the tools to see what’s going on under the hood.

A typical WebSocket lifecycle consists of three main areas: the opening handshake, sending and receiving frames, and the closing handshake. Each can present its own challenges. Outlining all of them here would be impossible, but I’ll show some methods of investigating should challenges arise while debugging.

The Handshake

The expected data the server receives from a valid client must include several HTTP headers like Host, Connection, Upgrade, Sec-WebSocket-Key, Sec-WebSocket-Version, and others that are optional to WebSocket. Proxies and security tools on some corporate networks might modify headers before they are transmitted to the server and could likely cause the handshake to fail. For testing purposes you can use OWASP ZAP. ZAP was designed to assist penetration testers with finding vulnerabilities in web applications, and you can use it to intercept ...

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