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P1sec / pycrate

A Python library to ease the development of encoders and decoders for various protocols and file formats; contains ASN.1 and CSN.1 compilers.
GNU Lesser General Public License v2.1
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Question about tagging in CHARACTER STRING #162

Closed russhousley closed 2 years ago

russhousley commented 2 years ago

The tag for string-value is set to 1.

    _CHARACTER_STRING_string_value = OCT_STR(name='string-value', mode=MODE_TYPE, tag=(1, TAG_CONTEXT_SPEC, TAG_EXPLICIT))

I expected data-value-descriptor to have a tag of 1, and string-value to have a tag of 2.

I realize that the constraints mean that data-value-descriptor will never be present, but I think that AUTOMATIC TAGS still assigns a tag number to it.

( WITH COMPONENTS { ... , data-value-descriptor ABSENT } )
p1-bmu commented 2 years ago

CHARACTER STRING is a predefined object, built here: https://github.com/P1sec/pycrate/blob/26c1a0a6bd26f9b0ab8f22e6efc619cbda3642b3/pycrate_asn1c/asnproc.py#L531 Components are explicitly tagged, so there is no AUTOMATIC TAGS implied.

What is your exact question ?

russhousley commented 2 years ago

In the ASN.1 specification, the syntax for EmbeddedPDV, EXTERNAL, and CHARACTER STRING are provided, and the text says that AUTOMATIC TAGS are used. I believe that the data-value-descriptor gets a tag of 1 (but it is never present) and that string-value should be given a tag of 2.

p1-bmu commented 2 years ago

You are correct: I was missing the data-value-descriptor component in the CHARACTER STRING definition. I just fixed it in master. Thank you.