Ponte changing binary data

I am trying to send binary data through ponte.
I do send these files with Copper and I send a file.
These are the binary values that should be sent:
[4, -30, -30, -9, -115, 0, 1, 0, 1, 0, 96, -32, 46, 0, 0, 0]
But as soon as ponte got this value in its payload it becomes this:
[4, -17, -65, -67, -17, -65, -67, -17, -65, -67, -17, -65, -67, 0, 1, 0, 1, 0, 96, -17, -65, -67, 46, 0, 0, 0]
Any idea how to fix this?

[psorowka]

EDIT: Ponte does not alter the payload at all. Your MQTT client might convert the payload to a Buffer, though, so your issue might be in providing an incompatible data format or convert back wrongly on the receiver.

You should provide some code, then we might be able to give a proper hint.

I have seen that with the buffer. Is it possible that this is the problem?
Actually I did went back to the base version an did not alter any of the code. Just receive and forward.

Thank you. I will have a look.

@psorowka
So I finally found out what the problem is. Java is sending the bytes as signed values.
Ponte is using unsigned values. Decimals larger than 127 get "damaged".
In Ponte I tried to create an Int8Array, fill it with data and send it. And I still got the same issue.
Any idea how to solve this?

[psorowka]

Ponte should not and never alter any data but only receive a chunk of bytes and deliver it. We are using ponte productively with all sorts of data and never got any problems (after a fix that is at least 1,5years old).

I am still assuming that your receiver and/or sender is handling the data wrongly. But again, for helping you we need much more info. E.g. which channels do you use (coap, mqtt, http?) for receiving and sending data, does the problem happen for retained messages, then: which persistence do you use plus sample code to reproduce the problem.

Thank you for your helo!
I am sending a binary message via CoAp (Copper).
The correct values arrive in ponte payload, but the values are converted from signed to unsigned (as you can see above) and are stored in a Buffer.
Now I send this payload (with correct Data but as unsigned values):

  that._persistence.storeRetained(packet, function() {
    that._broker.publish(topic, payload, {}, function() {
      res.statusCode = '2.04';
      res.end();
      that._ponte.emit('updated', topic, payload);
    });
  });

Using amqp as a broker to send it to RabbitMQ. A worker then grabs a this message and just prints out the bytes. All unsigned values above 127 are turned into "-17, -65, -67"

//Edit:
I "solved" the problem now by base64-encoding my data before sending.
At least for me all messages have been converted to unsigned int before sending, which caused my problem. Maybe it was the broker. Still thanks for all your help!

[psorowka]

What I observe is that not only are bytes converted from signed to unsigned but also the number of bytes gets longer.

As said, Ponte does not change the payload object at any time, which I also verified again in the CoAP code (which I don't use). I suspect the persistence or amqp conversion to be the problem. If I were you I would start inserting debug messages at certain points of the ponte code (e.g. in the storeRetained and lookupRetained callbacks) to narrow down the point at which the payload is changed.

[chombium]

Hi @zeConehead,

as @psorowka already mentioned, Ponte does not alter the payload.
Have you tried sending the same binary values with another CoAP client directly to Ponte without amqp?

Base 64 encoding is a workaround, I will do few tests tonight and if everything is good, you can close this ticket.

Best Regards,
Jovan

@chombium
Thank you as well!
Yes I tried another CoAP client. The problem is, as I said the conversion between unsigned an signed byte arrays. Even creating an Int8Array in Ponte and sending it to RabbitMQ does not help.
So it should be the broker or even Java that sends / receives the messages wrong.
I think I can close this issue already now.
Still thanks for your help!