I assume this is just a proof-of-concept..? Any web browser can render an HTML-view of a directory's file structure using FTP without any need for a complicated Mongoose-backend. HTTP is for transferring hypermedia, not for transferring files. For that, we use any file-transfer protocol such as FTP, AFP, SMB, SFTP, etc. Will you be adding some more functionality to this app or..?

What is needed is a good multi-purpose NAS app supporting FTP, AFP, SMB, and SFTP. You could use HTTPS to control the device, but it isn't for transferring files.