Should RemoteMessages support properties map per default?

[juliapampus]

Currently, e.g., the TransferRequestMessage has a properties map to allow sending custom key-value-pairs via the old ids protocol.

The dataspace protocol does not define extensible properties, so I would remove this map. However, with json-ld, it would be possible to provide this for any message type. For instance, if a dataspace would define its own profile of dspace, the EDC would automatically support it.

Approach would be to move the properties to the interface:

public interface RemoteMessage {

    /**
     * Returns the transport protocol this message must be sent over.
     */
    String getProtocol();

    /**
     * Returns the recipient's connector address.
     */
    String getConnectorAddress();

    /**
     * Allows for values of custom namespaces.
     */
   Map<String, Object> getProperties();

}

The serialization output of

Map.of("foo", "bar")

should be

{
   "foo": "bar"
}

not

{
   "properties": [
      {
         "foo": "bar"
      }
   ]
}

[jimmarino]

Yes, we should support that since the DSpace protocol is built on JSON-LD and embraces its extensibility. This also means at the protocol layer, the message should be transformed into a JSON-LD structure using the JSON-P API and compaction performed before sending the serialized form on the wire.