Harald Welte | e0f9ef1 | 2021-04-10 17:22:35 +0200 | [diff] [blame] | 1 | from construct import * |
Harald Welte | 2db5cfb | 2021-04-10 19:05:37 +0200 | [diff] [blame] | 2 | from pySim.utils import b2h, h2b, swap_nibbles |
Robert Falkenberg | b07a3e9 | 2021-05-07 15:23:20 +0200 | [diff] [blame] | 3 | import gsm0338 |
Harald Welte | e0f9ef1 | 2021-04-10 17:22:35 +0200 | [diff] [blame] | 4 | |
| 5 | """Utility code related to the integration of the 'construct' declarative parser.""" |
| 6 | |
| 7 | # (C) 2021 by Harald Welte <laforge@osmocom.org> |
| 8 | # |
| 9 | # This program is free software: you can redistribute it and/or modify |
| 10 | # it under the terms of the GNU General Public License as published by |
| 11 | # the Free Software Foundation, either version 2 of the License, or |
| 12 | # (at your option) any later version. |
| 13 | # |
| 14 | # This program is distributed in the hope that it will be useful, |
| 15 | # but WITHOUT ANY WARRANTY; without even the implied warranty of |
| 16 | # MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the |
| 17 | # GNU General Public License for more details. |
| 18 | # |
| 19 | # You should have received a copy of the GNU General Public License |
| 20 | # along with this program. If not, see <http://www.gnu.org/licenses/>. |
| 21 | |
| 22 | |
| 23 | class HexAdapter(Adapter): |
| 24 | """convert a bytes() type to a string of hex nibbles.""" |
| 25 | def _decode(self, obj, context, path): |
| 26 | return b2h(obj) |
| 27 | def _encode(self, obj, context, path): |
| 28 | return h2b(obj) |
| 29 | |
Harald Welte | 2db5cfb | 2021-04-10 19:05:37 +0200 | [diff] [blame] | 30 | class BcdAdapter(Adapter): |
| 31 | """convert a bytes() type to a string of BCD nibbles.""" |
| 32 | def _decode(self, obj, context, path): |
| 33 | return swap_nibbles(b2h(obj)) |
| 34 | def _encode(self, obj, context, path): |
| 35 | return h2b(swap_nibbles(obj)) |
| 36 | |
Robert Falkenberg | b07a3e9 | 2021-05-07 15:23:20 +0200 | [diff] [blame] | 37 | class Rpad(Adapter): |
| 38 | """ |
| 39 | Encoder appends padding bytes (b'\\xff') up to target size. |
| 40 | Decoder removes trailing padding bytes. |
| 41 | |
| 42 | Parameters: |
| 43 | subcon: Subconstruct as defined by construct library |
| 44 | pattern: set padding pattern (default: b'\\xff') |
| 45 | """ |
| 46 | |
| 47 | def __init__(self, subcon, pattern=b'\xff'): |
| 48 | super().__init__(subcon) |
| 49 | self.pattern = pattern |
| 50 | |
| 51 | def _decode(self, obj, context, path): |
| 52 | return obj.rstrip(self.pattern) |
| 53 | |
| 54 | def _encode(self, obj, context, path): |
| 55 | if len(obj) > self.sizeof(): |
| 56 | raise SizeofError("Input ({}) exceeds target size ({})".format(len(obj), self.sizeof())) |
| 57 | return obj + self.pattern * (self.sizeof() - len(obj)) |
| 58 | |
| 59 | class GsmStringAdapter(Adapter): |
| 60 | """Convert GSM 03.38 encoded bytes to a string.""" |
| 61 | |
| 62 | def __init__(self, subcon, codec='gsm03.38', err='strict'): |
| 63 | super().__init__(subcon) |
| 64 | self.codec = codec |
| 65 | self.err = err |
| 66 | |
| 67 | def _decode(self, obj, context, path): |
| 68 | return obj.decode(self.codec) |
| 69 | |
| 70 | def _encode(self, obj, context, path): |
| 71 | return obj.encode(self.codec, self.err) |
| 72 | |
Harald Welte | e0f9ef1 | 2021-04-10 17:22:35 +0200 | [diff] [blame] | 73 | def filter_dict(d, exclude_prefix='_'): |
| 74 | """filter the input dict to ensure no keys starting with 'exclude_prefix' remain.""" |
| 75 | res = {} |
| 76 | for (key, value) in d.items(): |
| 77 | if key.startswith(exclude_prefix): |
| 78 | continue |
| 79 | if type(value) is dict: |
| 80 | res[key] = filter_dict(value) |
| 81 | else: |
| 82 | res[key] = value |
| 83 | return res |
| 84 | |
| 85 | # here we collect some shared / common definitions of data types |
| 86 | LV = Prefixed(Int8ub, HexAdapter(GreedyBytes)) |
Robert Falkenberg | 9d16fbc | 2021-04-12 11:43:22 +0200 | [diff] [blame] | 87 | |
| 88 | # Default value for Reserved for Future Use (RFU) bits/bytes |
| 89 | # See TS 31.101 Sec. "3.4 Coding Conventions" |
| 90 | __RFU_VALUE = 0 |
| 91 | |
| 92 | # Field that packs Reserved for Future Use (RFU) bit |
| 93 | FlagRFU = Default(Flag, __RFU_VALUE) |
| 94 | |
| 95 | # Field that packs Reserved for Future Use (RFU) byte |
| 96 | ByteRFU = Default(Byte, __RFU_VALUE) |
| 97 | |
| 98 | # Field that packs all remaining Reserved for Future Use (RFU) bytes |
| 99 | GreedyBytesRFU = Default(GreedyBytes, b'') |
| 100 | |
| 101 | def BitsRFU(n=1): |
| 102 | ''' |
| 103 | Field that packs Reserved for Future Use (RFU) bit(s) |
| 104 | as defined in TS 31.101 Sec. "3.4 Coding Conventions" |
| 105 | |
| 106 | Use this for (currently) unused/reserved bits whose contents |
| 107 | should be initialized automatically but should not be cleared |
| 108 | in the future or when restoring read data (unlike padding). |
| 109 | |
| 110 | Parameters: |
| 111 | n (Integer): Number of bits (default: 1) |
| 112 | ''' |
| 113 | return Default(BitsInteger(n), __RFU_VALUE) |
| 114 | |
| 115 | def BytesRFU(n=1): |
| 116 | ''' |
| 117 | Field that packs Reserved for Future Use (RFU) byte(s) |
| 118 | as defined in TS 31.101 Sec. "3.4 Coding Conventions" |
| 119 | |
| 120 | Use this for (currently) unused/reserved bytes whose contents |
| 121 | should be initialized automatically but should not be cleared |
| 122 | in the future or when restoring read data (unlike padding). |
| 123 | |
| 124 | Parameters: |
| 125 | n (Integer): Number of bytes (default: 1) |
| 126 | ''' |
| 127 | return Default(Bytes(n), __RFU_VALUE) |
Robert Falkenberg | b07a3e9 | 2021-05-07 15:23:20 +0200 | [diff] [blame] | 128 | |
| 129 | def GsmString(n): |
| 130 | ''' |
| 131 | GSM 03.38 encoded byte string of fixed length n. |
| 132 | Encoder appends padding bytes (b'\\xff') to maintain |
| 133 | length. Decoder removes those trailing bytes. |
| 134 | |
| 135 | Exceptions are raised for invalid characters |
| 136 | and length excess. |
| 137 | |
| 138 | Parameters: |
| 139 | n (Integer): Fixed length of the encoded byte string |
| 140 | ''' |
| 141 | return GsmStringAdapter(Rpad(Bytes(n), pattern=b'\xff'), codec='gsm03.38') |