We have customers who are trying to download a setup.exe file over mobile connections that appear to be very slow.

They have reported that when they click on the downloaded setup.exe, the install wizard starts up, but part way through the wizard they get an error message indicating that a cab file is corrupt or missing.

They couriered a problem tablet to us, and we downloaded the file without a problem but I could replicate the problem by using https to download the file (https is normally used to access the rest of the site, although it is not necessary for the download). When I did this the downloaded file was 2.8MB. It should be 8MB.

I don't think that https is the root cause of the problem because I can see the download link in the browser history using http, so I know the customer tried to download using http. I think that the issue is that the poor connection is preventing a complete download, but the browser is acting as if it is complete.

Is there a way to ensure the file is downloaded fully, or not at all? Why does the browser not indicate that the download is incomplete?