libartifact: add BlobMountPaths()

The goal of this new interface is to expose the blob source path and the
target file name for a bind mount into a container.

libpod will call this and then take care of setting up the actual mounts
based on the returned paths.

Signed-off-by: Paul Holzinger <pholzing@redhat.com>

pkg/libartifact/store/store.go

@@ -346,6 +346,56 @@ func getArtifactAndImageSource(ctx context.Context, as ArtifactStore, nameOrDige
 	return arty, imgSrc, err
 }
 
+// BlobMountPaths allows the caller to access the file names from the store and how they should be mounted.
+func (as ArtifactStore) BlobMountPaths(ctx context.Context, nameOrDigest string, options *libartTypes.BlobMountPathOptions) ([]libartTypes.BlobMountPath, error) {
+	arty, imgSrc, err := getArtifactAndImageSource(ctx, as, nameOrDigest, &options.FilterBlobOptions)
+	if err != nil {
+		return nil, err
+	}
+	defer imgSrc.Close()
+
+	if len(options.Digest) > 0 || len(options.Title) > 0 {
+		digest, err := findDigest(arty, &options.FilterBlobOptions)
+		if err != nil {
+			return nil, err
+		}
+		// In case the digest is set we always use it as target name
+		// so we do not have to get the actual title annotation form the blob.
+		// Passing options.Title is enough because we know it is empty when digest
+		// is set as we only allow either one.
+		filename, err := generateArtifactBlobName(options.Title, digest)
+		if err != nil {
+			return nil, err
+		}
+		path, err := layout.GetLocalBlobPath(ctx, imgSrc, digest)
+		if err != nil {
+			return nil, err
+		}
+		return []libartTypes.BlobMountPath{{
+			SourcePath: path,
+			Name:       filename,
+		}}, nil
+	}
+
+	mountPaths := make([]libartTypes.BlobMountPath, 0, len(arty.Manifest.Layers))
+	for _, l := range arty.Manifest.Layers {
+		title := l.Annotations[specV1.AnnotationTitle]
+		filename, err := generateArtifactBlobName(title, l.Digest)
+		if err != nil {
+			return nil, err
+		}
+		path, err := layout.GetLocalBlobPath(ctx, imgSrc, l.Digest)
+		if err != nil {
+			return nil, err
+		}
+		mountPaths = append(mountPaths, libartTypes.BlobMountPath{
+			SourcePath: path,
+			Name:       filename,
+		})
+	}
+	return mountPaths, nil
+}
+
 // Extract an artifact to local file or directory
 func (as ArtifactStore) Extract(ctx context.Context, nameOrDigest string, target string, options *libartTypes.ExtractOptions) error {
 	arty, imgSrc, err := getArtifactAndImageSource(ctx, as, nameOrDigest, &options.FilterBlobOptions)

pkg/libartifact/types/config.go

@@ -25,3 +25,15 @@ type FilterBlobOptions struct {
 type ExtractOptions struct {
 	FilterBlobOptions
 }
+
+type BlobMountPathOptions struct {
+	FilterBlobOptions
+}
+
+// BlobMountPath contains the info on how the artifact must be mounted
+type BlobMountPath struct {
+	// Source path of the blob, i.e. full path in the blob dir.
+	SourcePath string
+	// Name of the file in the container.
+	Name string
+}