vibe.d: How to get the conent of a file upload ?

[wjoe via Digitalmars-d-learn]

I found this [1] but unfortunately the post this refers to is a 
dead link and the content, unfortunately, didn't tell me anything 
that I didn't already find in the docs.

What I can get from the form is the form fields with content, the 
field name for the file upload and the file name. But the file 
name is useless to me because I need the file content.

Where is it stored ?

[1] https://aberba.com/2017/multiple-file-upload-in-vibe-d/