For our chat application, we implemented our own http.Handler type (the room) in order to easily compile, execute, and deliver HTML content to browsers. Since this is a very simple but powerful interface, we are going to continue to use it wherever possible when adding functionality to our HTTP processing.
In order to determine whether a user is allowed to proceed, we will create an authorization wrapper handler that will perform the check and pass the execution on to the inner handler only if the user is authorized.
Our wrapper handler will satisfy the same http.Handler interface as the object inside it, allowing us to wrap any valid handler. In fact, even the authentication handler we are about to write could be later encapsulated inside a similar wrapper if required.
Chaining pattern when applied to HTTP handlers
The preceding diagram shows how this pattern could be applied in a more complicated HTTP handler scenario. Each object implements the http.Handler interface...