[ADD] index.html fallback

main.go

@@ -4,10 +4,24 @@ import (
 	"fmt"
 	"log"
 	"net/http"
+	"os"
+	"path"
 )
 
+func customFileServer(fs http.FileSystem) http.Handler {
+	fileServer := http.FileServer(fs)
+	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		_, err := fs.Open(path.Clean(r.URL.Path)) // Do not allow path traversals.
+		if os.IsNotExist(err) {
+			http.ServeFile(w, r, "./static/index.html")
+			return
+		}
+		fileServer.ServeHTTP(w, r)
+	})
+}
+
 func main() {
-	fs := http.FileServer(http.Dir("./static"))
+	fs := customFileServer(http.Dir("./static"))
 	http.Handle("/", fs)
 	fmt.Print("Listening on 4000")
 	err := http.ListenAndServe(":4000", nil)