How to server static files with virtual hosts functioality in Go - http

Question

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?

Answer 1

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.

Answer 2

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/")))