Generates a unique file name for a new user-specific data source.
If uid is non-null it will be used in the basename of the file, otherwise a unique
basename will be generated using util_generate_uid.
The returned File can then be passed to ServerSideSource. Unreference the File with unref when finished with it.
Note the data source file itself is not created here, only its name.
| uid |
unique identifier for a data source, or null |
|
the File for a new data source |