fixup: address review comments

pkg/mutate/tar.go

@@ -14,7 +14,6 @@ import (
 
 	v1 "github.com/google/go-containerregistry/pkg/v1"
 	"github.com/google/go-containerregistry/pkg/v1/tarball"
-	"github.com/google/go-containerregistry/pkg/v1/types"
 )
 
 type tarConverter struct {
@@ -50,9 +49,10 @@ func OptTarSkipWhiteoutConversion(b bool) TarConverterOpt {
 	}
 }
 
-// TarLayer converts the base layer into a layer using the tar format. A dir
-// must be specified, which is used as a working directory during conversion.
-// The caller is responsible for cleaning up dir.
+// TarFromSquashfsLayer returns an opener that will provide a TAR conversion of
+// the SquashFS format base layer. A dir must be specified, which is used as a
+// working directory during conversion. The caller is responsible for cleaning
+// up dir.
 //
 // By default, this will attempt to locate a suitable SquashFS to tar converter,
 // currently only 'sqfs2tar', via exec.LookPath. To specify a path to a specific
@@ -62,10 +62,15 @@ func OptTarSkipWhiteoutConversion(b bool) TarConverterOpt {
 // converted to AUFS whiteout markers in the TAR layer. This can be disabled,
 // e.g. where it is known that the layer is part of a squashed image that will
 // not have any whiteouts, using OptTarSkipWhiteourConversion.
-//
-// Note - when whiteout conversion is performed the base layer will be read
-// twice. Callers should ensure it is cached, and is not a streaming layer.
-func TarLayer(base v1.Layer, dir string, opts ...TarConverterOpt) (v1.Layer, error) {
+func TarFromSquashfsLayer(base v1.Layer, dir string, opts ...TarConverterOpt) (tarball.Opener, error) {
+	mt, err := base.MediaType()
+	if err != nil {
+		return nil, err
+	}
+	if mt != squashfsLayerMediaType {
+		return nil, fmt.Errorf("%w: %v", errUnsupportedLayerType, mt)
+	}
+
 	c := tarConverter{
 		dir:             dir,
 		convertWhiteout: true,
@@ -85,7 +90,7 @@ func TarLayer(base v1.Layer, dir string, opts ...TarConverterOpt) (v1.Layer, err
 		c.converter = path
 	}
 
-	return c.layer(base)
+	return c.opener(base), nil
 }
 
 // makeSquashfs returns a the path to a TAR file that contains the contents of
@@ -160,23 +165,3 @@ func (c *tarConverter) opener(l v1.Layer) tarball.Opener {
 		return pr, nil
 	}
 }
-
-// layer converts base to TAR format.
-func (c *tarConverter) layer(base v1.Layer) (v1.Layer, error) {
-	mt, err := base.MediaType()
-	if err != nil {
-		return nil, err
-	}
-
-	//nolint:exhaustive // Exhaustive cases not appropriate.
-	switch mt {
-	case squashfsLayerMediaType:
-		return tarball.LayerFromOpener(c.opener(base))
-
-	case types.DockerLayer, types.DockerUncompressedLayer, types.OCILayer, types.OCIUncompressedLayer:
-		return base, nil
-
-	default:
-		return nil, fmt.Errorf("%w: %v", errUnsupportedLayerType, mt)
-	}
-}

pkg/mutate/tar_test.go

@@ -14,7 +14,7 @@ import (
 	"github.com/sebdah/goldie/v2"
 )
 
-func Test_TARLayer(t *testing.T) {
+func Test_TarFromSquashfsLayer(t *testing.T) {
 	tests := []struct {
 		name              string
 		layer             v1.Layer
@@ -43,15 +43,15 @@ func Test_TARLayer(t *testing.T) {
 			name: "OverlayFSBlob",
 			layer: testLayer(t, "overlayfs-docker-v2-manifest", v1.Hash{
 				Algorithm: "sha256",
-				Hex:       "2addb7e8ed33f5f080813d437f455a2ae0c6a3cd41f978eaa05fc776d4f7a887",
+				Hex:       "1887579465ca7b9a51295c5c11db2c3b3b383699208576c3a466f25a3ea4d399",
 			}),
 			noConvertWhiteout: false,
 		},
 		{
 			name: "OverlayFSBlob_SkipWhiteoutConversion",
 			layer: testLayer(t, "overlayfs-docker-v2-manifest", v1.Hash{
 				Algorithm: "sha256",
-				Hex:       "2addb7e8ed33f5f080813d437f455a2ae0c6a3cd41f978eaa05fc776d4f7a887",
+				Hex:       "1887579465ca7b9a51295c5c11db2c3b3b383699208576c3a466f25a3ea4d399",
 			}),
 			noConvertWhiteout: true,
 		},
@@ -62,14 +62,14 @@ func Test_TARLayer(t *testing.T) {
 				t.Skip(err)
 			}
 
-			l, err := TarLayer(tt.layer, t.TempDir(),
+			opener, err := TarFromSquashfsLayer(tt.layer, t.TempDir(),
 				OptTarSkipWhiteoutConversion(tt.noConvertWhiteout),
 			)
 			if err != nil {
 				t.Fatal(err)
 			}
 
-			rc, err := l.Uncompressed()
+			rc, err := opener()
 			if err != nil {
 				t.Fatal(err)
 			}

test/images/gen_images.go

@@ -6,6 +6,7 @@ package main
 
 import (
 	"archive/tar"
+	"errors"
 	"fmt"
 	"io"
 	"os"
@@ -20,6 +21,7 @@ import (
 	"github.com/google/go-containerregistry/pkg/v1/partial"
 	"github.com/google/go-containerregistry/pkg/v1/remote"
 	"github.com/google/go-containerregistry/pkg/v1/tarball"
+	ocimutate "github.com/sylabs/oci-tools/pkg/mutate"
 )
 
 // Use a fixed digest, so that this is repeatable.
@@ -465,6 +467,85 @@ func generateManyLayerImage(path string) error {
 	return nil
 }
 
+var errMultipleImages = errors.New("multiple images found in index")
+
+func generateSquashFSImages(path string) error {
+	images := []struct {
+		source       string
+		destination  string
+		squashLayers bool
+	}{
+		{
+			source:       filepath.Join(path, "aufs-docker-v2-manifest"),
+			destination:  filepath.Join(path, "overlayfs-docker-v2-manifest"),
+			squashLayers: false, // need to preserve whiteout test files
+		},
+	}
+
+	for _, im := range images {
+		ii, err := layout.ImageIndexFromPath(im.source)
+		if err != nil {
+			return err
+		}
+
+		ix, err := ii.IndexManifest()
+		if err != nil {
+			return err
+		}
+		if len(ix.Manifests) != 1 {
+			return errMultipleImages
+		}
+
+		ih := ix.Manifests[0].Digest
+		img, err := ii.Image(ih)
+		if err != nil {
+			return err
+		}
+
+		if im.squashLayers {
+			img, err = ocimutate.Squash(img)
+			if err != nil {
+				return err
+			}
+		}
+
+		ms := []ocimutate.Mutation{}
+		ls, err := img.Layers()
+		if err != nil {
+			return err
+		}
+
+		for i, l := range ls {
+			squashfsLayer, err := ocimutate.SquashfsLayer(l, os.TempDir())
+			if err != nil {
+				return err
+			}
+			ms = append(ms, ocimutate.SetLayer(i, squashfsLayer))
+		}
+
+		img, err = ocimutate.Apply(img, ms...)
+		if err != nil {
+			return err
+		}
+
+		desc, err := partial.Descriptor(img)
+		if err != nil {
+			return err
+		}
+
+		ii = mutate.AppendManifests(empty.Index, mutate.IndexAddendum{
+			Add:        img,
+			Descriptor: *desc,
+		})
+
+		if _, err := layout.Write(im.destination, ii); err != nil {
+			return err
+		}
+	}
+
+	return nil
+}
+
 func main() {
 	path := "."
 	if len(os.Args) > 1 {
@@ -490,4 +571,9 @@ func main() {
 		fmt.Fprintln(os.Stderr, "Error:", err)
 		os.Exit(1)
 	}
+
+	if err := generateSquashFSImages(path); err != nil {
+		fmt.Fprintln(os.Stderr, "Error:", err)
+		os.Exit(1)
+	}
 }

test/images/overlayfs-docker-v2-manifest/blobs/sha256/853a0e609ae7e88e02720e4c7960c2526d968d30955fd8bc0fbc5dcfb1fbbebd

@@ -0,0 +1 @@
+{"architecture":"arm64","container":"b2af51419cbf516f3c99b877a64906b21afedc175bd3cd082eb5798e2f277bb4","created":"2022-03-19T16:12:58.923371954Z","docker_version":"20.10.12","history":[{"created":"2022-03-19T16:12:58.834095198Z","created_by":"/bin/sh -c #(nop) COPY file:a79dd5bda1e77203401956a93401d3aef45221fc750295a4291896f3386f4f54 in / "},{"created":"2022-03-19T16:12:58.923371954Z","created_by":"/bin/sh -c #(nop)  CMD [\"/hello\"]","empty_layer":true}],"os":"linux","rootfs":{"type":"layers","diff_ids":["sha256:2addb7e8ed33f5f080813d437f455a2ae0c6a3cd41f978eaa05fc776d4f7a887"]},"config":{"Cmd":["/hello"],"Env":["PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin"],"Image":"sha256:cc0fff24c4ece63ade5d9f549e42c926cf569112c4f5c439a4a57f3f33f5588b"},"variant":"v8"}

test/images/overlayfs-docker-v2-manifest/blobs/sha256/422627f9dff4768fe49c54173be06a1542cba43d4f4df60cf77f0f7251918ae8 → test/images/overlayfs-docker-v2-manifest/blobs/sha256/c6ec7891ab06148a4097f8d3d638671a2ca03945c8f400b4d50061c2560cb11a

@@ -1 +1 @@
-{"schemaVersion":2,"mediaType":"application/vnd.docker.distribution.manifest.v2+json","config":{"mediaType":"application/vnd.docker.container.image.v1+json","size":722,"digest":"sha256:b9cdf2f5591da561b6a8d7dd7515a4b37b11c72c25bd11327e50da1126f227b8"},"layers":[{"mediaType":"application/vnd.sylabs.image.layer.v1.squashfs","size":4096,"digest":"sha256:2addb7e8ed33f5f080813d437f455a2ae0c6a3cd41f978eaa05fc776d4f7a887"}]}
+{"schemaVersion":2,"mediaType":"application/vnd.docker.distribution.manifest.v2+json","config":{"mediaType":"application/vnd.docker.container.image.v1+json","size":788,"digest":"sha256:853a0e609ae7e88e02720e4c7960c2526d968d30955fd8bc0fbc5dcfb1fbbebd"},"layers":[{"mediaType":"application/vnd.sylabs.image.layer.v1.squashfs","size":4096,"digest":"sha256:2addb7e8ed33f5f080813d437f455a2ae0c6a3cd41f978eaa05fc776d4f7a887"}]}

test/images/overlayfs-docker-v2-manifest/index.json

@@ -1 +1 @@
-{"schemaVersion":2,"mediaType":"application/vnd.oci.image.index.v1+json","manifests":[{"mediaType":"application/vnd.docker.distribution.manifest.v2+json","size":421,"digest":"sha256:422627f9dff4768fe49c54173be06a1542cba43d4f4df60cf77f0f7251918ae8"}]}
+{"schemaVersion":2,"mediaType":"application/vnd.oci.image.index.v1+json","manifests":[{"mediaType":"application/vnd.docker.distribution.manifest.v2+json","size":421,"digest":"sha256:c6ec7891ab06148a4097f8d3d638671a2ca03945c8f400b4d50061c2560cb11a"}]}

test/images/overlayfs-docker-v2-manifest/oci-layout

@@ -0,0 +1,3 @@
+{
+    "imageLayoutVersion": "1.0.0"
+}