Re: Adding extra items to ASN.1

[Vasil Velichkov <vasil.velichkov@xxxxxxxxxxxx>]

Hi Simon,

To indicate that a type is extensible, put extension marker “...” in its 
definition.

Something like:

TestAttribs {
Test1           Test1Type OPTIONAL,
Test2           Test2Type OPTIONAL,
Test3           Test3Type OPTIONAL,
...
}

So later when you add newElement, receiving party will decode it like 
extenstion and can ignore it.

BR

Kearn, Simon (EXP) wrote:

> Dear All,
>
> I currently use SNACC 1.3 to build a number of message definitions, 
> and wanted to know if it was possible to add extra items to the end of 
> a type declaration that can be ignored by the other end.
>
> I have one system that I want to update regularly by adding new 
> elements but the other end that my system connects to I want to stay 
> as per its original declaration (the new elements would not 
> necessarily be used by the other system but perhaps by another system 
> that I have to connect to. I was under the impression that if I sent a 
> message with types declared and one of those types had an extra 
> optional element declared at the end, that the receiving system would 
> ignore it and carry on processing the rest of the message (similar to 
> Extensibility Implied in a way). As an example please see below;
>
> MsgOne {
>  HeaderInfo     HeaderInfoType,
>  TestAttribs    TestAttribsType OPTIONAL,
>  TestParams     TestParamsType OPTIONAL
> }
>
> HeaderInfo {
> HeaderID        HeaderIDType,
> HeaderName      HeaderNameType
> }
>
> TestAttribs {
> Test1           Test1Type OPTIONAL,
> Test2           Test2Type OPTIONAL,
> Test3           Test3Type OPTIONAL,
> newElement      NewElementType OPTIONAL         (New element added)
> }
>
> TestParams {
> TestP1          TestP1Type OPTIONAL,
> TestP2          TestP2Type OPTIONAL,
> TestP3          TestP3Type OPTIONAL,
> }
>
>
> In the above example I have declared a new optional type called 
> newElement. In the other system this new element is not declared so it 
> will not know about. What I wanted to do was send a message with the 
> new element and hope that the other end would ignore it. The ASN.1 
> code would suggest that when it sees this element it would just drop 
> out of the bottom of the code in a 'when others' declaration and carry 
> on processing the rest of the message, but all I get is an error 
> stating that there was a length discrepancy. The message would be 
> something like (in a simple format);
>
> MsgOne
>         HeaderID        1
>         HeaderName      Test
>         Test1           1      
>         Test2           2
>         Test3           3
>         newElement      new
>         TestP1          P1
>         TestP2          P2
>         TestP3          P3
>
> Thanks,
>
> Simon Kearn
> (+44 (0)23 9244 3188
> *simon.kearn@xxxxxxxx