Check media types when unmarshalling manifests

When unmarshalling manifests from JSON, check that the MediaType field
corresponds to the type that we are unmarshalling as. This makes sure
that when we retrieve a manifest from the manifest store, it will have
the same type as it was handled as before storing it in the manifest
store.

Signed-off-by: Owen W. Taylor <otaylor@fishsoup.net>

manifest/schema2/manifest_test.go

@@ -7,6 +7,7 @@ import (
 	"testing"
 
 	"github.com/docker/distribution"
+	"github.com/docker/distribution/manifest"
 )
 
 var expectedManifestSerialization = []byte(`{
@@ -26,9 +27,12 @@ var expectedManifestSerialization = []byte(`{
    ]
 }`)
 
-func TestManifest(t *testing.T) {
-	manifest := Manifest{
-		Versioned: SchemaVersion,
+func makeTestManifest(mediaType string) Manifest {
+	return Manifest{
+		Versioned: manifest.Versioned{
+			SchemaVersion: 2,
+			MediaType:     mediaType,
+		},
 		Config: distribution.Descriptor{
 			Digest:    "sha256:1a9ec845ee94c202b2d5da74a24f0ed2058318bfa9879fa541efaecba272e86b",
 			Size:      985,
@@ -42,6 +46,10 @@ func TestManifest(t *testing.T) {
 			},
 		},
 	}
+}
+
+func TestManifest(t *testing.T) {
+	manifest := makeTestManifest(MediaTypeManifest)
 
 	deserialized, err := FromStruct(manifest)
 	if err != nil {
@@ -109,3 +117,46 @@ func TestManifest(t *testing.T) {
 		t.Fatalf("unexpected size in reference: %d", references[0].Size)
 	}
 }
+
+func mediaTypeTest(t *testing.T, mediaType string, shouldError bool) {
+	manifest := makeTestManifest(mediaType)
+
+	deserialized, err := FromStruct(manifest)
+	if err != nil {
+		t.Fatalf("error creating DeserializedManifest: %v", err)
+	}
+
+	unmarshalled, descriptor, err := distribution.UnmarshalManifest(
+		MediaTypeManifest,
+		deserialized.canonical)
+
+	if shouldError {
+		if err == nil {
+			t.Fatalf("bad content type should have produced error")
+		}
+	} else {
+		if err != nil {
+			t.Fatalf("error unmarshaling manifest, %v", err)
+		}
+
+		asManifest := unmarshalled.(*DeserializedManifest)
+		if asManifest.MediaType != mediaType {
+			t.Fatalf("Bad media type '%v' as unmarshalled", asManifest.MediaType)
+		}
+
+		if descriptor.MediaType != MediaTypeManifest {
+			t.Fatalf("Bad media type '%v' for descriptor", descriptor.MediaType)
+		}
+
+		unmarshalledMediaType, _, _ := unmarshalled.Payload()
+		if unmarshalledMediaType != MediaTypeManifest {
+			t.Fatalf("Bad media type '%v' for payload", unmarshalledMediaType)
+		}
+	}
+}
+
+func TestMediaTypes(t *testing.T) {
+	mediaTypeTest(t, "", true)
+	mediaTypeTest(t, MediaTypeManifest, false)
+	mediaTypeTest(t, MediaTypeManifest+"XXX", true)
+}