container: add support for uploading to registries

Add a new generic container registry client via a new `container`
package. Use this to create a command line utility as well as a
new upload target for container registries.

The code uses the github.com/containers/* project and packages to
interact with container registires that is also used by skopeo,
podman et al. One if the dependencies is `proglottis/gpgme` that
is using cgo to bind libgpgme, so we have to add the corresponding
devel package to the BuildRequires as well as installing it on CI.

Checks will follow later via an integration test.

vendor/github.com/containers/image/v5/internal/blobinfocache/blobinfocache.go

@@ -0,0 +1,64 @@
+package blobinfocache
+
+import (
+	"github.com/containers/image/v5/pkg/compression"
+	compressiontypes "github.com/containers/image/v5/pkg/compression/types"
+	"github.com/containers/image/v5/types"
+	digest "github.com/opencontainers/go-digest"
+)
+
+// FromBlobInfoCache returns a BlobInfoCache2 based on a BlobInfoCache, returning the original
+// object if it implements BlobInfoCache2, or a wrapper which discards compression information
+// if it only implements BlobInfoCache.
+func FromBlobInfoCache(bic types.BlobInfoCache) BlobInfoCache2 {
+	if bic2, ok := bic.(BlobInfoCache2); ok {
+		return bic2
+	}
+	return &v1OnlyBlobInfoCache{
+		BlobInfoCache: bic,
+	}
+}
+
+type v1OnlyBlobInfoCache struct {
+	types.BlobInfoCache
+}
+
+func (bic *v1OnlyBlobInfoCache) RecordDigestCompressorName(anyDigest digest.Digest, compressorName string) {
+}
+
+func (bic *v1OnlyBlobInfoCache) CandidateLocations2(transport types.ImageTransport, scope types.BICTransportScope, digest digest.Digest, canSubstitute bool) []BICReplacementCandidate2 {
+	return nil
+}
+
+// CandidateLocationsFromV2 converts a slice of BICReplacementCandidate2 to a slice of
+// types.BICReplacementCandidate, dropping compression information.
+func CandidateLocationsFromV2(v2candidates []BICReplacementCandidate2) []types.BICReplacementCandidate {
+	candidates := make([]types.BICReplacementCandidate, 0, len(v2candidates))
+	for _, c := range v2candidates {
+		candidates = append(candidates, types.BICReplacementCandidate{
+			Digest:   c.Digest,
+			Location: c.Location,
+		})
+	}
+	return candidates
+}
+
+// OperationAndAlgorithmForCompressor returns CompressionOperation and CompressionAlgorithm
+// values suitable for inclusion in a types.BlobInfo structure, based on the name of the
+// compression algorithm, or Uncompressed, or UnknownCompression.  This is typically used by
+// TryReusingBlob() implementations to set values in the BlobInfo structure that they return
+// upon success.
+func OperationAndAlgorithmForCompressor(compressorName string) (types.LayerCompression, *compressiontypes.Algorithm, error) {
+	switch compressorName {
+	case Uncompressed:
+		return types.Decompress, nil, nil
+	case UnknownCompression:
+		return types.PreserveOriginal, nil, nil
+	default:
+		algo, err := compression.AlgorithmByName(compressorName)
+		if err == nil {
+			return types.Compress, &algo, nil
+		}
+		return types.PreserveOriginal, nil, err
+	}
+}

vendor/github.com/containers/image/v5/internal/blobinfocache/types.go

@@ -0,0 +1,45 @@
+package blobinfocache
+
+import (
+	"github.com/containers/image/v5/types"
+	digest "github.com/opencontainers/go-digest"
+)
+
+const (
+	// Uncompressed is the value we store in a blob info cache to indicate that we know that
+	// the blob in the corresponding location is not compressed.
+	Uncompressed = "uncompressed"
+	// UnknownCompression is the value we store in a blob info cache to indicate that we don't
+	// know if the blob in the corresponding location is compressed (and if so, how) or not.
+	UnknownCompression = "unknown"
+)
+
+// BlobInfoCache2 extends BlobInfoCache by adding the ability to track information about what kind
+// of compression was applied to the blobs it keeps information about.
+type BlobInfoCache2 interface {
+	types.BlobInfoCache
+	// RecordDigestCompressorName records a compressor for the blob with the specified digest,
+	// or Uncompressed or UnknownCompression.
+	// WARNING: Only call this with LOCALLY VERIFIED data; don’t record a compressor for a
+	// digest just because some remote author claims so (e.g. because a manifest says so);
+	// otherwise the cache could be poisoned and cause us to make incorrect edits to type
+	// information in a manifest.
+	RecordDigestCompressorName(anyDigest digest.Digest, compressorName string)
+	// CandidateLocations2 returns a prioritized, limited, number of blobs and their locations
+	// that could possibly be reused within the specified (transport scope) (if they still
+	// exist, which is not guaranteed).
+	//
+	// If !canSubstitute, the returned cadidates will match the submitted digest exactly; if
+	// canSubstitute, data from previous RecordDigestUncompressedPair calls is used to also look
+	// up variants of the blob which have the same uncompressed digest.
+	//
+	// The CompressorName fields in returned data must never be UnknownCompression.
+	CandidateLocations2(transport types.ImageTransport, scope types.BICTransportScope, digest digest.Digest, canSubstitute bool) []BICReplacementCandidate2
+}
+
+// BICReplacementCandidate2 is an item returned by BlobInfoCache2.CandidateLocations2.
+type BICReplacementCandidate2 struct {
+	Digest         digest.Digest
+	CompressorName string // either the Name() of a known pkg/compression.Algorithm, or Uncompressed or UnknownCompression
+	Location       types.BICLocationReference
+}