B4J Question messagearrived mqtt payload question about Hex array

[giggetto71]

Hi,
maybe this is a really stupid question and in that case I apologize in advance...
I am trying to receive on B4J mqtt client an HEX array payload. the issue (which I am sure has been already discussed but I did not find a clear answer) is that the method

Sub mqtt_MessageArrived (Topic As String, Payload() As Byte)

has the Payload() input parameter as Byte (signed byte -127 -> 128) so if the HEX number I get is below 128 then I get it right in the function payload : for example if I publish from another client (in this case I am using MqttBox) the Hex number 0x7F (127), the payload() array contains one element and its value is 127 (0x7F).
If from the test client I publish an hex number higher than 127 I get two elements in the array..For example with 0x80 published (128 decimal) the payload byte I get in the messagearrived function is a two elements array with element 0 equal to 0xFFFFFFC2 and element 1 equale to 0xFFFFFF80

Is there a way to get an unsigned bytes array ?
thanks

 

[DonManfred]

Maybe with this Method?

Sub ToUnsigned(b As Byte) As Int
   Return Bit.And(0xFF, b)
End Sub

 

[giggetto71]

thanks Don. my problem is not actually convert to unsigned. I would just like to understand why I get two bytes when on the B4j client when I publish a number higher than 129 on the mqttbox side. maybe it's just an issue on the mqttbox client..I have tried to publish from the B4j client and I did not notice any issue...
so really it's just an issue with MqttBox..I will make more tests.

 

[Erel]

an HEX array payload

I don't know what that means.

Please post the code that sends the message.

 

[giggetto71]

HI,
I cannot post the publish code because the client is a 3rd party product called MqttBox that I have been using many times for testing purposes. This product allows to send different types of payload:
- Strings/JSON/XML/Characters
- Binary Array
- Octal Array
- Decimal Array
- Hex Array

if I select the array type (even the decimal) I receive perfectly on B4J if the numbers are lower than 127 for example:

on messagearrived side I get:

If I try the same array with values higher than 127 this is what I get:

thanks for any help.

 

[Erel]

The client which is probably written in Java, converts the values larger than 127 to shorts = 2 bytes.