client: Fix failed to pull ubuntu image from docker.io

Manifests list feature in oci-distribution is already
implemented, default image in docker.io like busybox
use IMAGE_MANIFEST_LIST_MEDIA_TYPE, but ubuntu image
use OCI_IMAGE_INDEX_MEDIA_TYPE.

Fixes: #27

Signed-off-by: Wang, Arron <arron.wang@intel.com>

src/client.rs

@@ -696,6 +696,7 @@ impl Client {
             if media_type != IMAGE_MANIFEST_MEDIA_TYPE
                 && media_type != OCI_IMAGE_MEDIA_TYPE
                 && media_type != IMAGE_MANIFEST_LIST_MEDIA_TYPE
+                && media_type != OCI_IMAGE_INDEX_MEDIA_TYPE
             {
                 return Err(OciDistributionError::UnsupportedMediaTypeError(media_type));
             }
@@ -1521,6 +1522,7 @@ mod test {
     ];
     const GHCR_IO_IMAGE: &str = "ghcr.io/krustlet/oci-distribution/hello-wasm:v1";
     const DOCKER_IO_IMAGE: &str = "docker.io/library/hello-world@sha256:37a0b92b08d4919615c3ee023f7ddb068d12b8387475d64c622ac30f45c29c51";
+    const DOCKER_IO_UBUNTU: &str = "docker.io/library/ubuntu";
     const HTPASSWD: &str = "testuser:$2y$05$8/q2bfRcX74EuxGf0qOcSuhWDQJXrgWiy6Fi73/JM2tKC66qSrLve";
     const HTPASSWD_USERNAME: &str = "testuser";
     const HTPASSWD_PASSWORD: &str = "testpassword";
@@ -2375,6 +2377,20 @@ mod test {
         assert_eq!(manifest.config.media_type, manifest::WASM_CONFIG_MEDIA_TYPE);
     }
 
+    #[tokio::test]
+    async fn test_pull_docker_ubuntu() {
+        let reference = Reference::try_from(DOCKER_IO_UBUNTU).expect("failed to parse reference");
+        let mut c = Client::default();
+        assert!(c
+            .pull(
+                &reference,
+                &RegistryAuth::Anonymous,
+                vec![IMAGE_LAYER_GZIP_MEDIA_TYPE],
+            )
+            .await
+            .is_ok());
+    }
+
     #[tokio::test]
     #[ignore]
     async fn test_roundtrip_multiple_layers() {