copy/multiple: error on EnsureCompressionVariant and CopySpecificImages

Following option does not provides a way to detect and exclude
compression if it already exists, this feature may be implemented in
future.

See: #1987 (comment)

Signed-off-by: Aditya R <[email protected]>

copy/multiple.go

@@ -13,6 +13,7 @@ import (
  internalManifest "github.com/containers/image/v5/internal/manifest"
  "github.com/containers/image/v5/internal/set"
  "github.com/containers/image/v5/manifest"
+ "github.com/containers/image/v5/pkg/compression"
  digest "github.com/opencontainers/go-digest"
  imgspecv1 "github.com/opencontainers/image-spec/specs-go/v1"
  "github.com/sirupsen/logrus"
@@ -82,9 +83,31 @@ func platformCompressionMap(list internalManifest.List, instanceDigests []digest
  return res, nil
 }
 
+func validateCompressionVariantExists(input []OptionCompressionVariant) error {
+ for _, option := range input {
+ _, err := compression.AlgorithmByName(option.Algorithm.Name())
+ if err != nil {
+ return fmt.Errorf("invalid algorithm %q in option.EnsureCompressionVariantsExist: %w", option.Algorithm.Name(), err)
+ }
+ }
+ return nil
+}
+
 // prepareInstanceCopies prepares a list of instances which needs to copied to the manifest list.
 func prepareInstanceCopies(list internalManifest.List, instanceDigests []digest.Digest, options *Options) ([]instanceCopy, error) {
  res := []instanceCopy{}
+ if options.ImageListSelection == CopySpecificImages && len(options.EnsureCompressionVariantsExist) > 0 {
+ // List can already contain compressed instance for a compression selected in `EnsureCompressionVariantsExist`
+ // It’s unclear what it means when `CopySpecificImages` includes an instance in options.Instances,
+ // EnsureCompressionVariantsExist asks for an instance with some compression,
+ // an instance with that compression already exists, but is not included in options.Instances.
+ // We might define the semantics and implement this in the future.
+ return res, fmt.Errorf("EnsureCompressionVariantsExist is not implemented for CopySpecificImages")
+ }
+ err := validateCompressionVariantExists(options.EnsureCompressionVariantsExist)
+ if err != nil {
+ return res, err
+ }
  compressionsByPlatform, err := platformCompressionMap(list, instanceDigests)
  if err != nil {
  return nil, err