Function getApplier

plugins/transfer/plugin.go:167–231

(ic *plugin.InitContext, uc unpackConfiguration, p specs.Platform)

}

func getApplier(ic *plugin.InitContext, uc unpackConfiguration, p specs.Platform) (diff.Applier, bool, error) {
	if uc.Differ != "" {
		inst, err := ic.GetByID(plugins.DiffPlugin, uc.Differ)
		if err != nil {
			if uc.Optional {
				return nil, true, nil
			}
			return nil, false, fmt.Errorf("failed to get instance for diff plugin %q: %w", uc.Differ, err)
		}
		return inst.(diff.Applier), false, nil
	}

	var (
		applier   diff.Applier
		applierID string
	)
	for _, candidate := range ic.GetAll() {
		if candidate.Registration.Type != plugins.DiffPlugin {
			continue
		}
		var matched bool
		for _, pd := range candidate.Meta.Platforms {
			// Note that we must use the platforms supported by the differ to
			// match the platform in `UnpackConfiguration`.
			//
			// For example, a differ might only support "linux/amd64", while
			// the platform in `UnpackConfiguration` is "linux(+erofs)/amd64".
			// If we reverse this logic, this wrong differ will be applied.
			if platforms.Only(pd).Match(p) {
				matched = true
			}
		}
		if !matched {
			continue
		}
		if applier != nil {
			skippedApplier := candidate.Registration.ID

			// Prefer the default when multiple plugins match
			if skippedApplier == defaults.DefaultDiffer {
				skippedApplier = applierID
			}

			log.G(ic.Context).Warnf("multiple differs match for platform, set `differ` option to choose, skipping %q", skippedApplier)

			if candidate.Registration.ID == skippedApplier {
				continue
			}
		}
		inst, err := candidate.Instance()
		if err != nil {
			if plugin.IsSkipPlugin(err) {
				continue
			}
			if uc.Optional {
				return nil, true, nil
			}
			return nil, false, fmt.Errorf("failed to get instance for diff plugin %q: %w", candidate.Registration.ID, err)