Number Attributes Grammar Enhancement.

[sbernard31]

Looking at specification LWM2M-v1.2.1@core§Table: 7.3.2.-1 class Attributes you could see that number grammar are :

// for positive Integer
1*DIGIT

// for positive decimal 
1*DIGIT ["." 1*DIGIT]

And with #563 maybe also :

// for Integer
["-"] 1*DIGIT

// for decimal 
["-"] 1*DIGIT ["." 1*DIGIT]

This grammar allow number like : 0012 or -000055 or 000.256 or -000130.235 ...
This is a small issue but could be improved by using Cardinal as defined in https://datatracker.ietf.org/doc/html/rfc6690#section-2

cardinal       = "0" / ( %x31-39 *DIGIT )

So fixed rules will look like that 👇 using cardinal rule (and so refer to https://datatracker.ietf.org/doc/html/rfc6690#section-2)

// for positive Integer
cardinal

// for Integer
["-"] cardinal

// for positive decimal 
cardinal ["." 1*DIGIT]

// for decimal 
["-"] cardinal ["." 1*DIGIT]

If it is wanted to not refer to cardinal and only use core rules from https://www.rfc-editor.org/rfc/rfc5234#appendix-B.1
Then it will look like :

// for positive Integer
"0" / ( %x31-39 *DIGIT )

// for Integer
["-"] ("0" / ( %x31-39 *DIGIT ))

// for positive decimal 
("0" / ( %x31-39 *DIGIT )) ["." 1*DIGIT]

// for decimal 
["-"] ("0" / ( %x31-39 *DIGIT )) ["." 1*DIGIT]

[svdwalt007]

Analysis: Well-Founded Grammar Tightening

The proposal is well-founded. Leading zeros in numeric attributes create parsing ambiguity — notably, C's strtol with base=0 interprets "012" as octal 10, not decimal 12. Adopting the cardinal production from RFC 6690 is clean and aligns with CoAP's own conventions.

The proposed grammar is sound:

• positive integer: cardinal → "0" / (DIGIT1 *DIGIT) — prevents leading zeros
• integer: ["-"] cardinal
• decimal: ["-"] cardinal ["." 1*DIGIT]

This is a non-breaking change — no valid implementation produces 0012 as a notification attribute value. Any value currently in use that doesn't have leading zeros already conforms to the proposed grammar.

Recommend adopting for v1.3.

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