Refactor checking for compressed diff type

darstahl · darstahl · commit 95a0b3af95df · 2018-01-23T15:25:17.000-08:00
Signed-off-by: Darren Stahl &lt;darst@microsoft.com&gt;
diff --git a/diff/walking/differ.go b/diff/walking/differ.go
@@ -6,7 +6,6 @@ import (
 	"fmt"
 	"io"
 	"io/ioutil"
-	"strings"
 	"time"
 
 	"github.com/containerd/containerd/archive"
@@ -75,18 +74,10 @@ func (s *walkingDiff) Apply(ctx context.Context, desc ocispec.Descriptor, mounts
 			}).Debugf("diff applied")
 		}
 	}()
-	var isCompressed bool
-	switch desc.MediaType {
-	case ocispec.MediaTypeImageLayer, images.MediaTypeDockerSchema2Layer:
-	case ocispec.MediaTypeImageLayerGzip, images.MediaTypeDockerSchema2LayerGzip:
-		isCompressed = true
-	default:
-		// Still apply all generic media types *.tar[.+]gzip and *.tar
-		if strings.HasSuffix(desc.MediaType, ".tar.gzip") || strings.HasSuffix(desc.MediaType, ".tar+gzip") {
-			isCompressed = true
-		} else if !strings.HasSuffix(desc.MediaType, ".tar") {
-			return emptyDesc, errors.Wrapf(errdefs.ErrNotImplemented, "unsupported diff media type: %v", desc.MediaType)
-		}
+
+	isCompressed, err := images.IsCompressedDiff(ctx, desc.MediaType)
+	if err != nil {
+		return emptyDesc, errors.Wrapf(errdefs.ErrNotImplemented, "unsupported diff media type: %v", desc.MediaType)
 	}
 
 	var ocidesc ocispec.Descriptor
diff --git a/diff/windows/windows.go b/diff/windows/windows.go
@@ -5,7 +5,6 @@ package windows
 import (
 	"io"
 	"io/ioutil"
-	"strings"
 	"time"
 
 	winio "github.com/Microsoft/go-winio"
@@ -74,18 +73,10 @@ func (s *windowsDiff) Apply(ctx context.Context, desc ocispec.Descriptor, mounts
 			}).Debugf("diff applied")
 		}
 	}()
-	var isCompressed bool
-	switch desc.MediaType {
-	case ocispec.MediaTypeImageLayer, images.MediaTypeDockerSchema2Layer:
-	case ocispec.MediaTypeImageLayerGzip, images.MediaTypeDockerSchema2LayerGzip:
-		isCompressed = true
-	default:
-		// Still apply all generic media types *.tar[.+]gzip and *.tar
-		if strings.HasSuffix(desc.MediaType, ".tar.gzip") || strings.HasSuffix(desc.MediaType, ".tar+gzip") {
-			isCompressed = true
-		} else if !strings.HasSuffix(desc.MediaType, ".tar") {
-			return emptyDesc, errors.Wrapf(errdefs.ErrNotImplemented, "unsupported diff media type: %v", desc.MediaType)
-		}
+
+	isCompressed, err := images.IsCompressedDiff(ctx, desc.MediaType)
+	if err != nil {
+		return emptyDesc, errors.Wrapf(errdefs.ErrNotImplemented, "unsupported diff media type: %v", desc.MediaType)
 	}
 
 	ra, err := s.store.ReaderAt(ctx, desc.Digest)
diff --git a/images/image.go b/images/image.go
@@ -3,6 +3,7 @@ package images
 import (
 	"context"
 	"encoding/json"
+	"strings"
 	"time"
 
 	"github.com/containerd/containerd/content"
@@ -359,3 +360,22 @@ func RootFS(ctx context.Context, provider content.Provider, configDesc ocispec.D
 	}
 	return config.RootFS.DiffIDs, nil
 }
+
+// IsCompressedDiff returns true if mediaType is a known compressed diff media type.
+// It returns false if the media type is a diff, but not compressed. If the media type
+// is not a known diff type, it returns errdefs.ErrNotImplemented
+func IsCompressedDiff(ctx context.Context, mediaType string) (bool, error) {
+	switch mediaType {
+	case ocispec.MediaTypeImageLayer, MediaTypeDockerSchema2Layer:
+	case ocispec.MediaTypeImageLayerGzip, MediaTypeDockerSchema2LayerGzip:
+		return true, nil
+	default:
+		// Still apply all generic media types *.tar[.+]gzip and *.tar
+		if strings.HasSuffix(mediaType, ".tar.gzip") || strings.HasSuffix(mediaType, ".tar+gzip") {
+			return true, nil
+		} else if !strings.HasSuffix(mediaType, ".tar") {
+			return false, errdefs.ErrNotImplemented
+		}
+	}
+	return false, nil
+}
