Default configuration options for defined snaps in gadget.yaml

[Darren Wu]

gadget.yaml defines default configuration options for defined snaps, but ubuntu-image does not support it.

The gadget.yaml defines:
defaults:
  # Below is the store id of the wifi-ap snap
  2rGgvyaY0CCzlWuKAPwFtCWrgwkM8lqS:
    automatic-setup.disable: true

ubuntu-image error as:
ubuntu_image.parser.GadgetSpecificationError: Invalid gadget.yaml @ defaults:2rGgvyaY0CCzlWuKAPwFtCWrgwkM8lqS:automatic-setup.disable

The option is described in the official gadget.yaml format at https://github.com/snapcore/snapd/wiki/Gadget-snap

[Barry Warsaw (barry)]

I bet the problem is the dot in `automatic-setup.disable`.

As of 0.11 u-i parses and ignores the defaults: section but the regexp is probably too tight. It only supports a-z0-9 (case insensitive) and also dashes but not dots. The Gadget-snap spec doesn't really specify what's allowed but generally the same restriction as for the volume name is assumed (and volume name allowable characters *are* defined).

Should be an easy fix to allow dots in the defaults section; I'll ask on the snappy list about allowable characters.

[Simon Fels (morphis)]

@Barry: Thanks for taking this up! AFAIK the characters we need to allow are all those which are allowed for snap configuration options. Please not that the value for configuration items can be also any valid json data. See https://github.com/snapcore/snapd/blob/master/cmd/snap/cmd_set.go#L65

[Barry Warsaw (barry)]

@morphis: I think we'll just accept and ignore any values in the defaults section.