Message constructor
Message(])
Creates a Message with the provided properties.
Implementation
Message(this.sourceId, this.targetId, this.type, this.action,
[List<int>? payload, String? requestId]) {
this.requestId = requestId ?? '${ExtendedTimestamp.now(false)}';
if (payload != null) {
_payloadString = base64.encode(payload);
}
hash = integrityHash(CommunicationSecret([]));
}