code: public void dhtPutItem(byte[] publicKey, byte[] privateKey, Entry entry, byte[] salt) {
          s.dht_put_item(Vectors.bytes2byte_vector(publicKey),
                  Vectors.bytes2byte_vector(privateKey),
                  entry.swig(),
                  Vectors.bytes2byte_vector(salt));
      }
docs: calling the callback in between is convenient.