Serve homepage and static content from root

In Golang, how do I serve static content out of the root directory while still having a root directory handler for serving the homepage.

Use the following simple web server as an example:

package main

import (
	"fmt"
	"net/http"
)

func main() {
	http.HandleFunc("/", HomeHandler) // homepage
	http.ListenAndServe(":8080", nil)
}

func HomeHandler(w http.ResponseWriter, r *http.Request) {
	fmt.Fprintf(w, "HomeHandler")
}

If I do

http.Handle("/", http.FileServer(http.Dir("./")))

I receive a panic saying that I have two registrations for "/". Every Golang example I've found on the internet suggests serving their static content out of different directories, but that doesn't help much for things like sitemap.xml, favicon.ico, robots.txt and other files which are by-practice or mandated to always be served out of the root.

The behavior I seek is the behavior which is found in most web servers such as Apache, Nginx, or IIS, where it first traverses your rules, and if no rule is found it looks for an actual file, and if no file is found it 404s. My guess is that instead of writing a http.HandlerFunc, I need to write a http.Handler which checks if I am referencing a file with an extension, and if so checks for file existence and serves the file, otherwise it 404s or serves the homepage is the request was for "/". Unfortunately I'm not certain how to even begin such a task.

Part of me says I'm massively over-complicating the situation which makes me think that I am missing something? Any guidance would be appreciated.

An alternative (not using ServeMux) solution is to serve explicitly each file located in the root directory. The idea behind is to keep the number of root-based files very small.
sitemap.xml, favicon.ico, robots.txt are indeed mandated to be served out of the root :

package main

import (
	"fmt"
	"net/http"
)

func HomeHandler(w http.ResponseWriter, r *http.Request) {
	fmt.Fprintf(w, "HomeHandler")
}

func serveSingle(pattern string, filename string) {
	http.HandleFunc(pattern, func(w http.ResponseWriter, r *http.Request) {
		http.ServeFile(w, r, filename)
	})
}

func main() {
	http.HandleFunc("/", HomeHandler) // homepage

	// Mandatory root-based resources
	serveSingle("/sitemap.xml", "./sitemap.xml")
	serveSingle("/favicon.ico", "./favicon.ico")
	serveSingle("/robots.txt", "./robots.txt")

	// Normal resources
	http.Handle("/static", http.FileServer(http.Dir("./static/")))

	http.ListenAndServe(":8080", nil)
}

Please move all other resources (CSS, JS, etc.) to a proper subdirectory, e.g. /static/ .

One thing I thought of that might help you is that you can create your own ServeMux. I added to your example so that chttp is a ServeMux that you can have serve static files. The HomeHandler then checks to see if it should serve a file or not. I just check for a "." but you could do a lot of things. Just an idea, might not be what you are looking for.

package main

import (
    "fmt"
    "net/http"
    "strings"
)   

var chttp = http.NewServeMux()

func main() {

    chttp.Handle("/", http.FileServer(http.Dir("./")))

    http.HandleFunc("/", HomeHandler) // homepage
    http.ListenAndServe(":8080", nil)
}   

func HomeHandler(w http.ResponseWriter, r *http.Request) {

    if (strings.Contains(r.URL.Path, ".")) {
        chttp.ServeHTTP(w, r)
    } else {
        fmt.Fprintf(w, "HomeHandler")
    }   
} 

Using Gorilla mux package :

r := mux.NewRouter()

//put your regular handlers here

//then comes root handler
r.HandleFunc("/", homePageHandler)
//if a path not found until now, e.g. "/image/tiny.png" 
//this will look at "./public/image/tiny.png" at filesystem
r.PathPrefix("/").Handler(http.FileServer(http.Dir("./public/")))

http.Handle("/", r)
http.ListenAndServe(":8080", nil)