How to server static files with virtual hosts functioality in Go

How can I server static files (with FileServer) for a virtual host in Go?

If I have my own handler function, the task seems to be easily solvable [1]:

package main

import (
    "fmt"
    "net/http"
)

func main() {
    http.HandleFunc("/", func(w http.ResponseWriter, r *http.Request) {
        fmt.Fprintf(w, "Hello, world!")
    })
    http.HandleFunc("qa.example.com/", func(w http.ResponseWriter, r *http.Request) {
        fmt.Fprintf(w, "Hello, improved world!")
    })
    http.ListenAndServe(":8080", nil)
}

But what if I need to serve static files (with FileServer)
for a virtual host?

This

r.PathPrefix("qa.example.com/").Handler(http.FileServer(http.Dir("/static/qa/")))

does not work — it is just ignored.

What am I doing wrong?
Is this approach generally wrong?

package main

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

//go:embed *.go
var f embed.FS

func main() {
	// embed.Fs defaule modtime use now or env value.
	now := time.Now()
	// use mapping host to http.FileSystem
	vhosts := make(map[string]http.FileSystem)
	vhosts["qa.example.com"] = http.FS(f)    // from embed.FS
	vhosts["my.example.com"] = http.Dir(".") // from http.Dir

	http.HandleFunc("/", func(w http.ResponseWriter, r *http.Request) {
		fmt.Fprintf(w, "Hello, world!")
	})
	http.HandleFunc("/static/", func(w http.ResponseWriter, r *http.Request) {
		// find host
		fs, ok := vhosts[r.Host]
		if !ok {
			w.WriteHeader(404)
			w.Write([]byte("404 not found vhost"))
			return
		}
		// open file from http.FileSystem
		file, err := fs.Open(strings.TrimPrefix(r.URL.Path, "/static/"))
		if err != nil {
			// reference go1.18.3/net/http/fs.go toHTTPError function hander file error.
			w.Write([]byte("check err is 403 or 404 or 500"))
			return
		}
		stat, _ := file.Stat()
		// fix embed modtime is zero.
		modtime := stat.ModTime()
		if modtime.IsZero() {
			modtime = now
		}
		// response
		http.ServeContent(w, r, stat.Name(), modtime, file)

	})

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

run test exec command curl -H "Host: my.example.com" 127.0.0.1:8080/static/01.go, 01.go replacte your static filename.

Register a handler for host/path. Strip the /path part only when invoking the file handler.

This registration serves files for qa.example.com/static/* from the directory ./static/qa/.

http.HandleFunc("qa.example.com/static/", http.StripPrefix("/static", http.FileServer(http.Dir("./static/qa/")))