Functional Options for CreateContainer

[tri-adam]

sif.CreateContainer currently accepts a sif.CreateInfo:

sif/pkg/sif/sif.go

Lines 403 to 410 in 3a39a27

	// CreateInfo wraps all SIF file creation info needed.
	type CreateInfo struct {
	Pathname string // the end result output filename
	Launchstr string // the shell run command
	Sifversion string // the SIF specification version used
	ID uuid.UUID // image unique identifier
	InputDescr []DescriptorInput // slice of input info for descriptor creation
	}

With this pattern, users must understand the internals of SIF to effectively call CreateContainer. It would be better if these were defaulted, with potential overrides supplied via the functional options pattern. For example:

• Launchstr: default to sif.HdrLaunch
• Sifversion: default to sif.HdrVersion
• ID: default to a generated ID (perhaps the public API can avoid a UUID package at all, to prevent issues such as Replace Deprecated UUID Package #7).
• InputDescr: default to empty list, allow DescriptorInput via functional option.