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Replace the regex parsing by binary data parsing

environments/stage/deployments/50
Patrick Dohmen 2018-10-12 18:35:00 +02:00
parent 5b7dba4d6e
commit 6c898a167c
1 changed files with 33 additions and 18 deletions
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51
db/base/decoders/elfin_pp.py
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@ -1,31 +1,46 @@
#
# Preprocessor used in katai struct to remove the escape sequences of
# Preprocessor used in kaitai struct to remove the escape sequences of
# an ELFIN STAR telemetry frame
#
# Patrick Dohmen, DL4PD (dl4pd@darc.de)
# With the kind help of Mikhail Yakshin
#
# Usage in 'kaitai struct':
#
# - id: ax25_info
# type: elfin_tlm_data
# process: elfin_pp
# size-eos: true
# types:
# preprocessor:
# seq:
# - id: databuf
# process: elfin_pp
# size-eos: true
#
import re, binascii
import binascii
class ElfinPp:
def decode(self, bindata):
# convert bin to hex to use regex for substitution
hexdata = binascii.hexlify(bindata)
# substitute ELFIN STAR payload escape sequence
hexdata = re.sub('2727', '27', hexdata)
hexdata = re.sub('275[Ee]', '5E', hexdata)
hexdata = re.sub('2793', '93', hexdata)
# convert back to binary
returnbuf = binascii.unhexlify(hexdata)
return returnbuf
i = 0
binlen = len(bindata)
out = b''
while i < binlen:
ch = ord(bindata[i])
if ch == 0x27 and i + 1 < binlen:
next_ch = ord(bindata[i + 1])
if next_ch == 0x27 or next_ch == 0x5e or next_ch == 0x9e:
i += 1
out += bindata[i]
i += 1
return out
if __name__ == "__main__":
# some examples
dec = ElfinPp()
print binascii.hexlify(binascii.unhexlify('0011272722'))
print binascii.hexlify(dec.decode(binascii.unhexlify('0011272722')))
print binascii.hexlify(binascii.unhexlify('0011a2727220'))
print binascii.hexlify(dec.decode(binascii.unhexlify('0011a2727220')))
print binascii.hexlify(binascii.unhexlify('930027005e0027932727275e'))
print binascii.hexlify(dec.decode(binascii.unhexlify('930027005e0027932727275e')))