Move images to core/images

Signed-off-by: Derek McGowan <derek@mcg.dev>

core/images/diffid.go

@@ -0,0 +1,82 @@
+/*
+   Copyright The containerd Authors.
+
+   Licensed under the Apache License, Version 2.0 (the "License");
+   you may not use this file except in compliance with the License.
+   You may obtain a copy of the License at
+
+       http://www.apache.org/licenses/LICENSE-2.0
+
+   Unless required by applicable law or agreed to in writing, software
+   distributed under the License is distributed on an "AS IS" BASIS,
+   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+   See the License for the specific language governing permissions and
+   limitations under the License.
+*/
+
+package images
+
+import (
+	"context"
+	"io"
+
+	"github.com/opencontainers/go-digest"
+	ocispec "github.com/opencontainers/image-spec/specs-go/v1"
+
+	"github.com/containerd/containerd/v2/archive/compression"
+	"github.com/containerd/containerd/v2/core/content"
+	"github.com/containerd/containerd/v2/labels"
+	"github.com/containerd/log"
+)
+
+// GetDiffID gets the diff ID of the layer blob descriptor.
+func GetDiffID(ctx context.Context, cs content.Store, desc ocispec.Descriptor) (digest.Digest, error) {
+	switch desc.MediaType {
+	case
+		// If the layer is already uncompressed, we can just return its digest
+		MediaTypeDockerSchema2Layer,
+		ocispec.MediaTypeImageLayer,
+		MediaTypeDockerSchema2LayerForeign,
+		ocispec.MediaTypeImageLayerNonDistributable: //nolint:staticcheck // deprecated
+		return desc.Digest, nil
+	}
+	info, err := cs.Info(ctx, desc.Digest)
+	if err != nil {
+		return "", err
+	}
+	v, ok := info.Labels[labels.LabelUncompressed]
+	if ok {
+		// Fast path: if the image is already unpacked, we can use the label value
+		return digest.Parse(v)
+	}
+	// if the image is not unpacked, we may not have the label
+	ra, err := cs.ReaderAt(ctx, desc)
+	if err != nil {
+		return "", err
+	}
+	defer ra.Close()
+	r := content.NewReader(ra)
+	uR, err := compression.DecompressStream(r)
+	if err != nil {
+		return "", err
+	}
+	defer uR.Close()
+	digester := digest.Canonical.Digester()
+	hashW := digester.Hash()
+	if _, err := io.Copy(hashW, uR); err != nil {
+		return "", err
+	}
+	if err := ra.Close(); err != nil {
+		return "", err
+	}
+	digest := digester.Digest()
+	// memorize the computed value
+	if info.Labels == nil {
+		info.Labels = make(map[string]string)
+	}
+	info.Labels[labels.LabelUncompressed] = digest.String()
+	if _, err := cs.Update(ctx, info, "labels"); err != nil {
+		log.G(ctx).WithError(err).Warnf("failed to set %s label for %s", labels.LabelUncompressed, desc.Digest)
+	}
+	return digest, nil
+}