manifest: explicitly error if whitespace reconstruction has failed

This behavior should not break any more use cases than before.
Previously, if the mismatch occured, we would actually push a manifest
that we then never referred to in the manifest list! If this was done in
a new repository, the command would fail with an obscure error from the
registry - the content wouldn't exist with the descriptor we expect it
to.

Signed-off-by: Justin Chadwell <me@jedevc.com>

cli/command/manifest/push.go

@@ -218,28 +218,41 @@ func buildPutManifestRequest(imageManifest types.ImageManifest, targetRef refere
 		return mountRequest{}, err
 	}
 
+	// Attempt to reconstruct indentation of the manifest to ensure sha parity
+	// with the registry.
+	//
+	// This is neccessary because our previous internal storage format did not
+	// preserve whitespace. If we don't have the newer format present, we can
+	// attempt the reconstruction like before, but explicitly error if the
+	// reconstruction failed!
 	switch {
 	case imageManifest.SchemaV2Manifest != nil:
-		// This indentation has to be added to ensure sha parity with the registry
 		dt, err := json.MarshalIndent(imageManifest.SchemaV2Manifest, "", "   ")
 		if err != nil {
 			return mountRequest{}, err
 		}
-		// indent only the DeserializedManifest portion of this, in order to maintain parity with the registry
-		// and not alter the sha
+
+		dig := imageManifest.Descriptor.Digest
+		if dig2 := dig.Algorithm().FromBytes(dt); dig != dig2 {
+			return mountRequest{}, errors.Errorf("internal digest mismatch for %s: expected %s, got %s", imageManifest.Ref, dig, dig2)
+		}
+
 		var manifest schema2.DeserializedManifest
 		if err = manifest.UnmarshalJSON(dt); err != nil {
 			return mountRequest{}, err
 		}
 		imageManifest.SchemaV2Manifest = &manifest
 	case imageManifest.OCIManifest != nil:
-		// This indentation has to be added to ensure sha parity with the registry
 		dt, err := json.MarshalIndent(imageManifest.OCIManifest, "", "  ")
 		if err != nil {
 			return mountRequest{}, err
 		}
-		// indent only the DeserializedManifest portion of this, in order to maintain parity with the registry
-		// and not alter the sha
+
+		dig := imageManifest.Descriptor.Digest
+		if dig2 := dig.Algorithm().FromBytes(dt); dig != dig2 {
+			return mountRequest{}, errors.Errorf("internal digest mismatch for %s: expected %s, got %s", imageManifest.Ref, dig, dig2)
+		}
+
 		var manifest ocischema.DeserializedManifest
 		if err = manifest.UnmarshalJSON(dt); err != nil {
 			return mountRequest{}, err