Better error message when getting legacy manifests (#600)

Signed-off-by: Valentin Delaye <jonesbusy@users.noreply.github.com>

Author: jonesbusy

src/main/java/land/oras/OCI.java

@@ -231,7 +231,8 @@ protected boolean isIndexMediaType(String mediaType) {
      */
     protected boolean isManifestMediaType(String mediaType) {
         return mediaType.equals(Const.DEFAULT_MANIFEST_MEDIA_TYPE)
-                || mediaType.equals(Const.DOCKER_MANIFEST_MEDIA_TYPE);
+                || mediaType.equals(Const.DOCKER_MANIFEST_MEDIA_TYPE)
+                || mediaType.equals(Const.LEGACY_MANIFEST_MEDIA_TYPE);
     }
 
     /**

src/main/java/land/oras/Registry.java

@@ -691,6 +691,11 @@ public Manifest getManifest(ContainerRef containerRef) {
             throw new OrasException(
                     "Expected manifest but got index. Probably a multi-platform image instead of artifact");
         }
+        if (contentType.equals(Const.LEGACY_MANIFEST_MEDIA_TYPE)) {
+            throw new OrasException(
+                    "Schema version 1 with manifest media type '%s' is not supported. Please use schema version 2 or higher"
+                            .formatted(contentType));
+        }
         String json = descriptor.getJson();
         String digest = descriptor.getDigest();
         if (digest == null) {

src/main/java/land/oras/utils/Const.java

@@ -163,6 +163,12 @@ private Const() {
      */
     public static final String DEFAULT_INDEX_MEDIA_TYPE = "application/vnd.oci.image.index.v1+json";
 
+    /**
+     * Legacy manifest media type for Docker distribution manifest v1, which is a JWS (JSON Web Signature) format and is not widely used anymore, but some registries may still support it for backward compatibility
+     * Ensure to raise a proper error message when we encounter this media type, as it is not supported by the SDK
+     */
+    public static final String LEGACY_MANIFEST_MEDIA_TYPE = "application/vnd.docker.distribution.manifest.v1+prettyjws";
+
     /**
      * The artifact manifest media type
      */