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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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Accessing message name for RRC messages #123

Closed aveer28 closed 3 years ago

aveer28 commented 3 years ago

I'm decoding RRC messages as follows

defs = RRCLTE.EUTRA_RRC_Definitions
msg = defs.BCCH_DL_SCH_Message

msg.from_uper(unhexlify(input))
decoded = msg._val

Is there any way to access the message name e.g. measurementControl from the decoded or other object.

p1-bmu commented 3 years ago

Sorry, but I cannot really understand your question. Please show what's inside your decoded dict, and explain what other object you are considering.

aveer28 commented 3 years ago

Here is an example of the decoded dict. 

{'message': ('c1', ('systemInformationBlockType1', {'cellAccessRelatedInfo': {'plmn-IdentityList': [{'plmn-Identity': {'mcc': [2, 3, 4], 'mnc': [1, 0]}, 'cellReservedForOperatorUse': 'reserved'}, {'plmn-Identity': {'mcc': [2, 3, 4], 'mnc': [1, 5]}, 'cellReservedForOperatorUse': 'notReserved'}], 'trackingAreaCode': (8254, 16), 'cellIdentity': (128062750, 28), 'cellBarred': 'notBarred', 'intraFreqReselection': 'allowed', 'csg-Indication': False}, 'cellSelectionInfo': {'q-RxLevMin': -62}, 'p-Max': 23, 'freqBandIndicator': 20, 'schedulingInfoList': [{'si-Periodicity': 'rf16', 'sib-MappingInfo': []}, {'si-Periodicity': 'rf16', 'sib-MappingInfo': ['sibType3']}, {'si-Periodicity': 'rf16', 'sib-MappingInfo': ['sibType5']}, {'si-Periodicity': 'rf16', 'sib-MappingInfo': ['sibType6']}, {'si-Periodicity': 'rf16', 'sib-MappingInfo': ['sibType7']}], 'si-WindowLength': 'ms20', 'systemInfoValueTag': 16}))}

For me to access the message name systemInformationBlockType1 or other params, I would have to step down through the dict and tuples. I was wondering if there was an easier way to access this, as it appears for the NAS decoder, which creates objects corresponding to the different message types. I realise that NAS is more advanced and thus this functionality may not exist.

p1-bmu commented 3 years ago

As shortly introduced in https://github.com/P1sec/pycrate/wiki/Using-the-pycrate-asn1-runtime#rrc-3g, you can use get_at() and get_val_at() methods to navigate within an object or its value. This however does not save you to know the object content, which only depends of the compiled ASN.1 schema, and nothing else.