Rationale

There are a number of special use cases that use the ubuntu download service whose requirements are different to those of the normal confined applications. The metadata dictionary allows these special use cases to provide information to perform certain actions.

Post download execution

• Use case: click-scope

• Metadata key: post-download-command

The click scope requires from the download manager executes a command line for each download performed. The command executed by the download manager can be passed via the post-download-command metadata key. If the command is correctly executed the finish signal is executed else the error signal will be used.

Object path

• Use case: click-scope

• Metadata key: objectpath

Ir order to reduce the number of dbus calls that the click-scope has to performed it was agreed that if a download contains an uuid in the objectpath metadata key this uuid will be used. This allows the click-scope to be able to anticipate the object path to be used by such a download and increases its speed.

Local file

• Use case: ubuntu-image-updates

• Metadata key: local-path

The ubuntu-image-updates can provide the local paths of a download either via the createDownloadGroup method or using the local-path key in the metadata. When that data is provided the download manager will download each download to the designated path else it will generate a secure path as the one used in AppArmor confined applications.