This middleware returns a file’s contents from disk in the body response. When initialized it can accept an optional ‘Cache-Control’ header which will be set when a response containing a file’s contents is delivered.
This middleware will render the file specified in `env[“PATH_INFO”]` where the base path is in the root directory. For example if the root is set to `public/` then a request with `env[“PATH_INFO”]` of `assets/application.js` will return a response with contents of a file located at `public/assets/application.js` if the file exists. If the file does not exist a 404 “File not Found” response will be returned.