My idea concerning implicit tags used in the asn2eth compiler and my dissectors is little
bit different.
If implicit tag ocurs it is checked in the 'parent structure' and it is not cut but
passesd to the 'field decoder' with implicit_tag=TRUE.
And the 'field decoder' does not check tag value but can use all information about length
etc. Event it can pass that tag into the next subdecoder if nested.
Which constructs for CMIP could make problem with that approach?
Could you send me an exmaple?
Regards,
Tom
ronnie sahlberg wrote:
the idea was to make some CMIP stuff decode properly.
the idea is that IF implitic_tag is set, then the identifier and
length is not checked at all
instead it is assume the value spans until the end of the tvb, some
cases therefore need, to create a new sub tvb that only spans the
length.
i.e. CHOICE {
[1] IMPLICIT integer foo;
then the identifier and length is read in the coice dissector, and
since it was IMPLICIT
it creates a new tvb only containing as much data as length indicated.
then it calls the subdissector for integer/foo since implicit_tag
is now set instead of reading the identifier/length it assumes the
length is tvb_length_remaining()
it was the best i could come up with to handle some of the constructs for CMIP.
If you have a better approach, please have a go at it.
I can provide the cmip captures i had problems with for you to test with.
On Tue, 25 Jan 2005 16:00:32 +0100, Tomas Kukosa
<tomas.kukosa@xxxxxxxxxxx> wrote:
Hi Ronnie,
I have found with delay that some my dissectors does not work properly.
The reason is different behaviour of dissect_ber_sequence() if implicit_tag is TRUE.
What was your idea concernig implicit tag?
My original idea was that BER identifier and length is decoded for implicit tag too but
the tag is not checked.
But after your changes BER identifier and length is not decoded anymore for implicit tag.
Could we clarify it?
Regards,
Tom
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