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Make possible to store longer values than 128 bytes, by implementing the tlv documentation #3

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Make possible to store longer values than 128 bytes, by implementing the tlv documentation #3

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91bf8cb
Make possible to make longer tlvs following the explanation here http…
Nov 7, 2022
98ade10
Remove the padding
Nov 7, 2022
8c3ff67
Remove redundant print
Nov 7, 2022
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40 changes: 31 additions & 9 deletions pytlv/TLV.py
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Original file line number Diff line number Diff line change
Expand Up @@ -186,7 +186,7 @@ def __init__(self, tags=None):
self.tags = emv_tags

self.tlv_string = ''

self.tag_lengths = set()
for tag, tag_name in self.tags.items():
self.tag_lengths.add(len(tag))
Expand All @@ -197,21 +197,34 @@ def parse(self, tlv_string):
"""
parsed_data = OrderedDict()
self.tlv_string = tlv_string

i = 0
while i < len(self.tlv_string):
while i < len(self.tlv_string):
tag_found = False

for tag_length in self.tag_lengths:
for tag, tag_name in self.tags.items():
if self.tlv_string[i:i+tag_length] == tag:
try:
value_length = int(self.tlv_string[i+tag_length:i+tag_length+2], 16)
offset = 2
_val_length = self.tlv_string[i+tag_length:i+tag_length+2]

if _val_length == '81':
offset +=2
value_length = int(self.tlv_string[i+tag_length:i+tag_length+offset][2:], 16)
elif _val_length == '82':
offset += 4
value_length = int(self.tlv_string[i + tag_length:i + tag_length + offset][4:], 16)

elif _val_length == '83':
offset += 4
value_length = int(self.tlv_string[i + tag_length:i + tag_length + offset][6:], 16)
else:
value_length = int(_val_length, 16)

except ValueError:
raise ValueError('Parse error: tag ' + tag + ' has incorrect data length')

value_start_position = i+tag_length+2
value_end_position = i+tag_length+2+value_length*2
value_start_position = i+tag_length+offset
value_end_position = i+tag_length+offset+value_length*2

if value_end_position > len(self.tlv_string):
raise ValueError('Parse error: tag ' + tag + ' declared data of length ' + str(value_length) + ', but actual data length is ' + str(int(len(self.tlv_string[value_start_position-1:-1])/2)))
Expand All @@ -227,6 +240,15 @@ def parse(self, tlv_string):
raise ValueError(msg)
return parsed_data

def compute_tag_length(self, length:int):
if length <= 128:
return hexify(length)
if 128 < length <= 255:
return '81'+hexify(length)
elif 255 < length <= 65535:
return '82'+hexify(length)
else:
return '83'+hexify(length)

def build(self, data_dict):
"""
Expand All @@ -239,7 +261,7 @@ def build(self, data_dict):
if divmod(len(value), 2)[1] == 1:
raise ValueError('Invalid value length - the length must be even')

self.tlv_string = self.tlv_string + tag.upper() + hexify(len(value) / 2) + value.upper()
self.tlv_string = self.tlv_string + tag.upper() + self.compute_tag_length(len(value) // 2) + value.upper()

return self.tlv_string

Expand All @@ -263,7 +285,7 @@ def _parse_tvr(self, tvr, left_indent='', desc_column_width=48):
if byte_value > 0:
byte_value_binary = '{0:b}'.format(byte_value).rjust(8, '0')
tvr_dump = tvr_dump + '\n' + left_indent + 'Byte {}: [{}]\n'.format(byte, byte_value_binary)

for j in range(0, 8):
if (byte_value >> j & 1) == 1:
tvr_dump = tvr_dump + left_indent + tvr_bit_names[byte][j][:desc_column_width].rjust(desc_column_width, ' ') + ': [1]\n'
Expand Down
5 changes: 5 additions & 0 deletions pytlv/tests.py
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Original file line number Diff line number Diff line change
Expand Up @@ -117,6 +117,11 @@ def test_tlv_parse_known_tag_no_length_4(self):
with self.assertRaisesRegex(ValueError, 'Parse error: tag 9F02 declared data of length 4, but actual data length is 3'):
self.tlv.parse('9F0204010203')

def test_parse_long_tlv(self):
self.tlv = TLV(['9F06', '9F22', 'DF03', 'DF04', 'DF02'])
ff = "9F0605A0000000049F2201F3DF0314A69AC7603DAF566E972DEDC2CB433E07E8B01A9ADF040103DF02819098F0C770F23864C2E766DF02D1E833DFF4FFE92D696E1642F0A88C5694C6479D16DB1537BFE29E4FDC6E6E8AFD1B0EB7EA0124723C333179BF19E93F10658B2F776E829E87DAEDA9C94A8B3382199A350C077977C97AFF08FD11310AC950A72C3CA5002EF513FCCC286E646E3C5387535D509514B3B326E1234F9CB48C36DDD44B416D23654034A66F403BA511C5EFA3"
print(self.tlv.parse(ff))

"""
tlv.build()
"""
Expand Down