Negative values handling for Write Attribute

[PFnord]

Question

Hello everyone,

I am trying to have a HTTP PUT method that will handle negative values for Attributes. Does leshan not handle negative values for them?
I have checked the code for DoubleAttributeModel and LongAttributeModel here but it seems to be checking for a DIGIT as the first char:

int start = parser.getPosition();
parser.consumeDIGIT();

This seems to throw an exception as the "-" sign (or % in the case of %2D) is not handled. So I have not found a way to use either curl or python requests library to write a negative attribute to my resource without altering the java code. Am I missing something?

Thanks in advance

[sbernard31]

I'm not sure to understand.
I guess you try to send WriteAttributeRequest using REST API of leshan-server-demo ?

If yes, when I look at LWM2M-v1.1.1@core§Table: 5.1.2.-2 class Attributes, I can not see attribute which supports negative value. (see CoRE Link param column)

Did I miss something ?

[PFnord]

Yes, I am mostly using REST API.

I agree, the specs seems to specify 1*DIGIT["." 1*DIGIT] for greater than for example, but being a float type I would have assumed a possibility of attributes being negative.

Here's where this can be of use. For Radio signal strength, the value is usually represented as negative, so using the greater than or less than should be, in general, a negative threshold. Maybe I'm looking at this the wrong way but it does seem to be that the specs are quite vague on this.

[sbernard31]

For Radio signal strength, the value is usually represented as negative, so using the greater than or less than should be, in general, a negative threshold.

🤔 you maybe find a specification issue ? At least, this seems NOT fixed in LwM2m-v1.2.1 ...

Let's open an issue at OMA to try to get an answer : OpenMobileAlliance/OMA_LwM2M_for_Developers#563

Please do not hesitate to add a comment to OMA issue above with your real use case ☝️.

[PFnord]

Thanks for that, I'll keep an eye on the answer!
I know other implementation of LwM2M handles the "-" sign for attributes so this could just be a small inconsistency/oversight in the documentation. 😄

[sbernard31]

I hope we will get an answer 🤞
By the way, thx for reporting this 🙏

[sbernard31]

We can some news from OMA :

• Using negative value in write attributes ? OpenMobileAlliance/OMA_LwM2M_for_Developers#563 (comment)

So I think I will adapt the code and this should be available for next milestone release 2.0.0-M14.

[sbernard31]

I created a PR about that : #1535

[sbernard31]

This is now integrated in master and should be available in next release 2.0.0-M14.

For pmin, pmax, epmin and epmax let's wait for OMA answer : OpenMobileAlliance/OMA_LwM2M_for_Developers#563 (comment)

[PFnord]

That's a very nice change, thanks, I will try and test that locally!

[sbernard31]

Some more question about attribute type : #1583