@SuppressWarnings("removal") // TODO: Remove on Vespa 9
        public Routable decode(DocumentDeserializer in) {
            byte pri = in.getByte(null); // TODO: ignore on Vespa 9
            in.getInt(null); // Ignored load type
            DocumentMessage msg = doDecode(in);
            if (msg != null) {
                msg.setPriority(DocumentProtocol.getPriority(pri));
            }
            return msg;
        }
This method decodes a message from the given deserializer. You are guaranteed to only receive byte buffers
generated by a previous call to {@link #doEncode(DocumentMessage, DocumentSerializer)}.
<p>
This method is NOT exception safe. Return null to signal failure.

@param deserializer The deserializer to use for decoding.
@return The decoded message.
documentapi/src/main/java/com/yahoo/documentapi/messagebus/protocol/RoutableFactories60.java