Router: Route StaticFS() not found to Router's NoRoute() (#1663)

Closes #1220

routergroup.go

@@ -185,11 +185,19 @@ func (group *RouterGroup) StaticFS(relativePath string, fs http.FileSystem) IRou
 func (group *RouterGroup) createStaticHandler(relativePath string, fs http.FileSystem) HandlerFunc {
 	absolutePath := group.calculateAbsolutePath(relativePath)
 	fileServer := http.StripPrefix(absolutePath, http.FileServer(fs))
-	_, nolisting := fs.(*onlyfilesFS)
+
 	return func(c *Context) {
-		if nolisting {
+		file := c.Param("filepath")
+
+		// Check if file exists and/or if we have permission to access it
+		if _, err := fs.Open(file); err != nil {
 			c.Writer.WriteHeader(http.StatusNotFound)
+			c.handlers = group.engine.allNoRoute
+			// Reset index
+			c.index = -1
+			return
 		}
+
 		fileServer.ServeHTTP(c.Writer, c.Request)
 	}
 }