#840 ASN Library

[Wajih]

Dear TCL Experts and Developer,

Recently , I used TCL Asn linrary package which made
lots of thing easier. However, I found that bugs or
possibilites of improvement.

Please check the following and see if it will be a
good idea to make following changes:

1. TAG Verification
In all of the asn Package, after reading TAG value it
is verified with Universal TAG , e.g.

if {$tag != 0x02} {
return -code error \
[format "Expected Integer (0x02), but got
%02x" $tag]
}

This , however , is true only when universal TAGs are
in use. In many cases private TAG are also use for
the data encoding.

I think , such checks should be removed as it should
be consider programmer responsibility to verify if
the TAG is expected , universal or private. Library
should not provide any restriction.

2. TAG Length
The library package consider TAG length as one byte
only. This , however , might not be true in some case
where the TAG can be of 2 bytes.

This should be corrected with the possibility of TAG
with variable length.

3. PeekBytes Procedure?
There is no procedure for PeekBytes. Sometimes it is
necessary to read the byte/bytes without affecting
the original Data. ::asn::asnPeekByte though exist
but there is nothing like PeekBytes

4. Output of getByte
The output byte of asnGetByte gives the result in
decimal format. Since it is binary data I will
suggest the result should be hex coded format to keep
all things in same format.

5. Introduction of Choce Structure ( and others )
The ASN library package should be able to handle
other kinds of ASN structure e.g. Choice structure

The Choice structure allows to match one of the
various possibilites:

Choice :: {

1. Money
2. Car
3. Nothing

}

With this type of encoding any one of the above
choice may happen. Therefore , there should be a
possibility of passing TAG values as an argument and
the procedure should try which to match the TAG and
then pass the value back of the choice which actually
appeared .

Similarly , we have SEQOF , SETOF types of data
structure which should also be consider.

Many thanks!

Wajih

[Michael Schlenker]

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Some of this is fixed in asn 0.8. I added a asn::peekTag, and some others to handle multi-byte tags and retag things. Not the best solution currently, but works.

PeekBytes is basically not needed, as the asn data is just a string. If you want a peek at the first x bytes, simply use string range for now, it works fine with binary data.