laforge has uploaded this change for review. ( https://gerrit.osmocom.org/c/pysim/+/27169 )

Change subject: construct: Add Construct for variable-length int 'GreedyInteger' ......................................................................

construct: Add Construct for variable-length int 'GreedyInteger'

We have a number of integers with variable-length encoding, so add a Construct for this. Naming inspired by GreedyBytes.

Related to https://github.com/construct/construct/issues/962

Change-Id: Ic6049b74ea3705fda24855f34b4a1d5f2c9327f7 --- M pySim/construct.py 1 file changed, 54 insertions(+), 1 deletion(-)

git pull ssh://gerrit.osmocom.org:29418/pysim refs/changes/69/27169/1

diff --git a/pySim/construct.py b/pySim/construct.py index e3f6a88..1783753 100644 --- a/pySim/construct.py +++ b/pySim/construct.py @@ -2,12 +2,14 @@ from construct.core import EnumIntegerString import typing from construct import * +from construct.core import evaluate, bytes2integer, integer2bytes +from construct.lib import integertypes from pySim.utils import b2h, h2b, swap_nibbles import gsm0338

"""Utility code related to the integration of the 'construct' declarative parser."""

-# (C) 2021 by Harald Welte laforge@osmocom.org +# (C) 2021-2022 by Harald Welte laforge@osmocom.org # # This program is free software: you can redistribute it and/or modify # it under the terms of the GNU General Public License as published by @@ -184,3 +186,54 @@ n (Integer): Fixed length of the encoded byte string ''' return GsmStringAdapter(Rpad(Bytes(n), pattern=b'\xff'), codec='gsm03.38') + +class GreedyInteger(Construct): + """A variable-length integer implementation, think of combining GrredyBytes with BytesInteger.""" + def __init__(self, signed=False, swapped=False): + super().__init__() + self.signed = signed + self.swapped = swapped + + def _parse(self, stream, context, path): + data = stream_read_entire(stream, path) + if evaluate(self.swapped, context): + data = swapbytes(data) + try: + return bytes2integer(data, self.signed) + except ValueError as e: + raise IntegerError(str(e), path=path) + + def __bytes_rqd(self, i): + if self.signed: + raise IntegerError("FIXME: Implement support for encoding signed integer") + if i <= 0xff: + return 1 + elif i <= 0xffff: + return 2 + elif i <= 0xffffff: + return 3 + elif i <= 0xffffffff: + return 4 + elif i <= 0xffffffffff: + return 5 + elif i <= 0xffffffffffff: + return 6 + elif i <= 0xffffffffffffff: + return 7 + elif i <= 0xffffffffffffffff: + return 8 + else: + raise IntegerError(f"value {i} is out of range") + + def _build(self, obj, stream, context, path): + if not isinstance(obj, integertypes): + raise IntegerError(f"value {obj} is not an integer", path=path) + length = self.__bytes_rqd(obj) + try: + data = integer2bytes(obj, length, self.signed) + except ValueError as e: + raise IntegerError(str(e), path=path) + if evaluate(self.swapped, context): + data = swapbytes(data) + stream_write(stream, data, length, path) + return obj