getWriteLength method
Gets the length of the write data when WriteTo will be called. A subclass that overrides writeTo must also overwrite this method.
Implementation
int getWriteLength() {
var headerLength = 0;
final enc = MqttEncoding();
headerLength += enc.getByteCount(protocolName);
headerLength += 1; // protocolVersion
headerLength += MqttConnectFlags.getWriteLength();
headerLength += 2; // keepAlive
headerLength += 1; // returnCode
headerLength += enc.getByteCount(topicName.toString());
headerLength += 2; // MessageIdentifier
return headerLength;
}