[erlang-questions] ASN.1 PER Does Not Correctly Handle Value Range Size Constraint

[Behdad Forghani]

Oops, I meant to delete the SIZE OF from my email, you are correct there 
as well.

Behdad Forghani wrote:
> Hi Kenneth,
>
> You are quite right about bit strings. I am not sure about SIZE OF. I 
> had missed the (SIZE(
>
> This was a test I had written based on the following NBAP specification:
> HARQ-MemoryPartitioningInfoExtForMIMO ::= SEQUENCE (SIZE (4|6|8)) OF 
> HARQ-MemoryPartitioningItem
>
> It is not a syntax error because ASN.1 grammar defines;
> TypeWithConstraint ::=
> .
> |
> SEQUENCE Constraint OF Type
> |
>
> But, I agree this is a semantic error.
>
> Thanks for clarifying this.
>
> Regards,
> Behdad
>
> Kenneth Lundin wrote:
>> Hi,
>>
>> You have spotted a weak point in the ASN.1 compiler but it is not the
>> type of wrong behaviour as
>> you think.
>>
>> For BIT STRING and SEQUENCE OF the standard defines that the following
>> constraints are
>> applicable:
>> - Single value,
>> - Contained Subtype
>> - Size constraint
>>
>> But not Value-range
>>
>> On Sat, May 21, 2011 at 9:35 PM, Behdad Forghani
>> <behdad.forghani@REDACTED>  wrote:
>>> Hi,
>>>
>>> I have tested this on R14B02.
>>>
>>> I noticed that ASN.1 compiler does not handle value range size 
>>> constraints
>>> for SEQUENCE OF and BIT STRING.
>>>
>>> For example:
>>> Abs ::= BIT STRING(0|1|7)
>> I don't know how to interpret  Abs, what does it mean? i.e. the 0|1|7
>> is it value 0, 1, 7? it is certainly not
>> the size since then you have to write (SIZE(0|1|7))
>>
>>> Bbs ::= BIT STRING(3..18)
>> This is a value range which is clearly not applicable (the compiler
>> should have rejected this)
>>
>> If you want a SIZE constraint you should write BIT STRING (SIZE(3..18))
>>
>>> Cbs ::= BIT STRING
>>>
>>>
>>> Abs has a size constraint of 0..7 and Bbs, 3..18.
>> These are not size constraints they are value ranges. Which are not 
>> applicable.
>> I have to check the standard regarding the union to see what it means
>> for a BIT STRING if it is
>> applicable at all.
>>> All three of the above will be encoded identically as length 
>>> indeterminant
>>> as 0x07DA. This is only correct for Cbs. The problem seems to be that
>>> encode_bit_string calls get_constraint(C,'SizeConstraint').
>>>
>>> However the constraint for the Abs is a UNION and for Bbs a 
>>> ValueRange. It
>>> seems to me the support for both constraints needs to be added.
>> No I don't think so. I think it should be added functionality to
>> reject constraints which are not applicable for the type in question.
>>> Just FYI, trying to give something back to the community. If I am 
>>> correct, I
>>> can easily fix it. In that case, can you enlighten me on how to 
>>> submit my
>>> code changes?
>>>
>>> Behdad
>>> _______________________________________________
>>> erlang-questions mailing list
>>> erlang-questions@REDACTED
>>> http://erlang.org/mailman/listinfo/erlang-questions
>>>
>> /Kenneth Erlang/OTP, Ericsson
>