Extend Applier's Apply() method with an optional options parameter

Extend the Applier interface's Apply method with an optional
options parameter.

For the container image encryption we intend to use the options
parameter to pass image decryption parameters ('dcparameters'),
which are primarily (privatte) keys, in form of a JSON document
under the map key '_dcparameters', and pass them to the Applier's
Apply() method. This helps us to access decryption keys and start
the pipeline with the layer decryption before the layer data are
unzipped and untarred.

Signed-off-by: Stefan Berger <stefanb@linux.ibm.com>
Signed-off-by: Harshal Patil <harshal.patil@in.ibm.com>

diff.go

@@ -45,9 +45,15 @@ type diffRemote struct {
 	client diffapi.DiffClient
 }
 
-func (r *diffRemote) Apply(ctx context.Context, diff ocispec.Descriptor, mounts []mount.Mount) (ocispec.Descriptor, error) {
+func (r *diffRemote) Apply(ctx context.Context, desc ocispec.Descriptor, mounts []mount.Mount, opts ...diff.ApplyOpt) (ocispec.Descriptor, error) {
+	var config diff.ApplyConfig
+	for _, opt := range opts {
+		if err := opt(&config); err != nil {
+			return ocispec.Descriptor{}, err
+		}
+	}
 	req := &diffapi.ApplyRequest{
-		Diff:   fromDescriptor(diff),
+		Diff:   fromDescriptor(desc),
 		Mounts: fromMounts(mounts),
 	}
 	resp, err := r.client.Apply(ctx, req)

diff/apply/apply.go

@@ -53,7 +53,7 @@ var emptyDesc = ocispec.Descriptor{}
 // Apply applies the content associated with the provided digests onto the
 // provided mounts. Archive content will be extracted and decompressed if
 // necessary.
-func (s *fsApplier) Apply(ctx context.Context, desc ocispec.Descriptor, mounts []mount.Mount) (d ocispec.Descriptor, err error) {
+func (s *fsApplier) Apply(ctx context.Context, desc ocispec.Descriptor, mounts []mount.Mount, opts ...diff.ApplyOpt) (d ocispec.Descriptor, err error) {
 	t1 := time.Now()
 	defer func() {
 		if err == nil {

diff/diff.go

@@ -51,6 +51,13 @@ type Comparer interface {
 	Compare(ctx context.Context, lower, upper []mount.Mount, opts ...Opt) (ocispec.Descriptor, error)
 }
 
+// ApplyConfig is used to hold parameters needed for a apply operation
+type ApplyConfig struct {
+}
+
+// ApplyOpt is used to configure an Apply operation
+type ApplyOpt func(*ApplyConfig) error
+
 // Applier allows applying diffs between mounts
 type Applier interface {
 	// Apply applies the content referred to by the given descriptor to
@@ -58,7 +65,7 @@ type Applier interface {
 	// implementation and content descriptor. For example, in the common
 	// case the descriptor is a file system difference in tar format,
 	// that tar would be applied on top of the mounts.
-	Apply(ctx context.Context, desc ocispec.Descriptor, mount []mount.Mount) (ocispec.Descriptor, error)
+	Apply(ctx context.Context, desc ocispec.Descriptor, mount []mount.Mount, opts ...ApplyOpt) (ocispec.Descriptor, error)
 }
 
 // WithMediaType sets the media type to use for creating the diff, without

diff/lcow/lcow.go

@@ -95,7 +95,7 @@ func NewWindowsLcowDiff(store content.Store) (CompareApplier, error) {
 // Apply applies the content associated with the provided digests onto the
 // provided mounts. Archive content will be extracted and decompressed if
 // necessary.
-func (s windowsLcowDiff) Apply(ctx context.Context, desc ocispec.Descriptor, mounts []mount.Mount) (d ocispec.Descriptor, err error) {
+func (s windowsLcowDiff) Apply(ctx context.Context, desc ocispec.Descriptor, mounts []mount.Mount, opts ...diff.ApplyOpt) (d ocispec.Descriptor, err error) {
 	t1 := time.Now()
 	defer func() {
 		if err == nil {

diff/windows/windows.go

@@ -87,7 +87,7 @@ func NewWindowsDiff(store content.Store) (CompareApplier, error) {
 // Apply applies the content associated with the provided digests onto the
 // provided mounts. Archive content will be extracted and decompressed if
 // necessary.
-func (s windowsDiff) Apply(ctx context.Context, desc ocispec.Descriptor, mounts []mount.Mount) (d ocispec.Descriptor, err error) {
+func (s windowsDiff) Apply(ctx context.Context, desc ocispec.Descriptor, mounts []mount.Mount, opts ...diff.ApplyOpt) (d ocispec.Descriptor, err error) {
 	t1 := time.Now()
 	defer func() {
 		if err == nil {

services/diff/local.go

@@ -99,8 +99,10 @@ func (l *local) Apply(ctx context.Context, er *diffapi.ApplyRequest, _ ...grpc.C
 		mounts  = toMounts(er.Mounts)
 	)
 
+	var opts []diff.ApplyOpt
+
 	for _, differ := range l.differs {
-		ocidesc, err = differ.Apply(ctx, desc, mounts)
+		ocidesc, err = differ.Apply(ctx, desc, mounts, opts...)
 		if !errdefs.IsNotImplemented(err) {
 			break
 		}