How to Web2py custom download function - python-2.7

Question

I'm developing a simple webapp in web2py and I want to create a link that let's the user download a file. Like this:
<a href="{{=URL('download',args = FILE)}}" download>
However, I want to do this without having to pass the FILE to the user in the page handler. I want to retrieve an ID from the server asynchronously that will correspond to the file I want to download and then pass it to a custom download function like this:
<a href="{{=URL('custom_download',args = FILEID)}}" download>
This way, I will be able to upload files to the server asynchronously, (I already figured out how to do that) and the download link on the page for that file will work right away without having to reload the page.
So, on the server side, I would do something like this:
def custom_download():
download_row = db(db.computers.FILEID == request.args(0)).select()
download_file = download_row.filefield
return download_file
However, I'm not entirely sure what I need to write in order for this to work.

Answer 1

I assumed that your files are stored in uploads folder, then your custom download function will be:
def custom_download():
download_row = db(db.computers.FILEID == request.args(0)).select().first()
download_file = download_row.filefield
# Name of file is table_name.field.XXXXX.ext, so retrieve original file name
org_file_name = db.computers.filefield.retrieve(download_file)[0]
file_header = "attachment; filename=" + org_file_name
response.headers['ContentType'] = "application/octet-stream"
response.headers['Content-Disposition'] = file_header
file_full_path = os.path.join(request.folder, 'uploads', download_file)
fh = open(file_full_path, 'rb')
return response.stream(fh)