How to restrict web server written in golang to allow a particular address instead of a pattern?

Question

When I use

http.HandleFunc(\"/\", serveRest)  //serveRest is the method to handle request
http.ListenAndServe(\"localhost:4000\", nil)

It will

Answer 1

The URL pattern to which you register your handlers is documented in the http.ServeMux type:

Patterns name fixed, rooted paths, like "/favicon.ico", or rooted subtrees, like "/images/" (note the trailing slash). Longer patterns take precedence over shorter ones, so that if there are handlers registered for both "/images/" and "/images/thumbnails/", the latter handler will be called for paths beginning "/images/thumbnails/" and the former will receive requests for any other paths in the "/images/" subtree.

Note that since a pattern ending in a slash names a rooted subtree, the pattern "/" matches all paths not matched by other registered patterns, not just the URL with Path == "/".

So unfortunately there is no pattern which matches only the root ("/").

But you can easily check this in your handler, and do whatever you want to if the request path is not the root:

func serveRest(w http.ResponseWriter, r *http.Request) {
    if r.URL.Path != "/" {
        w.Write([]byte("Not root!"))
        return
    }
    
    w.Write([]byte("Hi, this is the root!"))
}

If you want to return HTTP 404 Not found error for non-roots:

func serveRest(w http.ResponseWriter, r *http.Request) {
    if r.URL.Path != "/" {
        http.NotFound(w, r)
        return
    }

    w.Write([]byte("Hi!"))
}

And Go tutorial: https://tour.golang.org/

Also check out the Go tag info here on SO, it has a section Go Tutorials.

Answer 2

You could check out https://github.com/julienschmidt/httprouter

Per its readme:

Only explicit matches: With other routers, like http.ServeMux, a requested URL path could match multiple patterns. Therefore they have some awkward pattern priority rules, like longest match or first registered, first matched. By design of this router, a request can only match exactly one or no route. As a result, there are also no unintended matches, which makes it great for SEO and improves the user experience.

Here is some good video content to get started in Go.