Sometimes we want to serve files from disk whose name is not a direct mapping from the URL. For example, let's say that you have an image and you want to allow the client to request the images in different sizes by setting a query parameter. e.g.
Clearly, we can not just map the path info portion of the URL to a file disk, because all the different sizes have the same name -- only the query parameter is different. Instead, the application will use some custom algorithm to calculate where the image lives on the disk. It may even need to generate the resized image on-demand. Once the application knows where the file lives on disk it can use serveFile to send that file as a Response using sendFile:
The first argument is a function which calculates the mime-type for a FilePath. The second argument is path to the file to send. So we might do something like:
Note that even though the file is named photo_medium.jpg on the disk, that name is not exposed to the client. They will only see the name they requested, i.e., photo.jpg.
guessContentTypeM will guess the content-type of the file by looking at the filename extension. But, if our photo app only supports JPEG files, there is no need to guess. Furthermore, the name of the file on the disk may not even have the proper extension. It could just be the md5sum of the file or something. So we can also hardcode the correct content-type:
The following, example attempts to serve its own source code for any incoming request.
[Source code for the app is here.]