1550797 - Improve BITS support for handling multiple downloads

Status: NEW

(Toolkit :: Application Update, defect, P3)

Description

[Robin Steuber (she/her) [:bytesized]]

BITS Download support was added in Bug 1520321, but has only been used in the updater to download one file at a time. In theory, this download mechanism should be able to support multiple downloads from multiple components.

The main barriers to this at the moment are initialization and download destination selection.

The initialization is a problem because it only happens once and affects all downloads. If different components want a different timeout lengths, whichever one asks second is out of luck.

The download destination is a related problem. To prevent the BITS download mechanism from downloading files to malicious locations, the initialization sets an immutable download directory, which all downloads must be downloaded to. The updater currently sets this to the update directory. If other Firefox components ever need to download files to anywhere other than the update directory, the way this works will need to be changed.