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construct/tlv: Pass optional 'context' into construct decoder/encoder

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The context is some opaque dictionary that can be used by the
constructs; let's allow the caller of parse_construct,  from_bytes,
from_tlv to specify it.

Also, when decoding a TLV_IE_Collection, pass the decode results of
existing siblings via the construct.

Change-Id: I021016aaa09cddf9d36521c1a54b468ec49ff54d
This commit is contained in:
Harald Welte
2023-12-17 10:07:01 +01:00
committed by laforge
parent 188869568a
commit caef0df663
2 changed files with 36 additions and 31 deletions
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7
pySim/construct.py
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@@ -200,13 +200,16 @@ def normalize_construct(c):
return r
def parse_construct(c, raw_bin_data: bytes, length: typing.Optional[int] = None, exclude_prefix: str = '_'):
def parse_construct(c, raw_bin_data: bytes, length: typing.Optional[int] = None, exclude_prefix: str = '_', context: dict = {}):
"""Helper function to wrap around normalize_construct() and filter_dict()."""
if not length:
length = len(raw_bin_data)
parsed = c.parse(raw_bin_data, total_len=length)
parsed = c.parse(raw_bin_data, total_len=length, **context)
return normalize_construct(parsed)
def build_construct(c, decoded_data, context: dict = {}):
"""Helper function to handle total_len."""
return c.build(decoded_data, total_len=None, **context)
# here we collect some shared / common definitions of data types
LV = Prefixed(Int8ub, HexAdapter(GreedyBytes))

60
pySim/tlv.py
View File

@@ -26,7 +26,7 @@ from pySim.utils import comprehensiontlv_encode_tag, comprehensiontlv_parse_tag
from pySim.utils import bertlv_parse_one, comprehensiontlv_parse_one
from pySim.utils import bertlv_parse_tag_raw, comprehensiontlv_parse_tag_raw
from pySim.construct import parse_construct, LV, HexAdapter, BcdAdapter, BitsRFU, GsmStringAdapter
from pySim.construct import build_construct, parse_construct, LV, HexAdapter, BcdAdapter, BitsRFU, GsmStringAdapter
from pySim.exceptions import *
import inspect
@@ -84,15 +84,15 @@ class Transcodable(abc.ABC):
self.decoded = None
self._construct = None
def to_bytes(self) -> bytes:
def to_bytes(self, context: dict = {}) -> bytes:
"""Convert from internal representation to binary bytes. Store the binary result
in the internal state and return it."""
if self.decoded == None:
do = b''
elif self._construct:
do = self._construct.build(self.decoded, total_len=None)
do = build_construct(self._construct, self.decoded, context)
elif self.__class__._construct:
do = self.__class__._construct.build(self.decoded, total_len=None)
do = build_construct(self.__class__._construct, self.decoded, context)
else:
do = self._to_bytes()
self.encoded = do
@@ -102,16 +102,16 @@ class Transcodable(abc.ABC):
def _to_bytes(self):
raise NotImplementedError('%s._to_bytes' % type(self).__name__)
def from_bytes(self, do: bytes):
def from_bytes(self, do: bytes, context: dict = {}):
"""Convert from binary bytes to internal representation. Store the decoded result
in the internal state and return it."""
self.encoded = do
if self.encoded == b'':
self.decoded = None
elif self._construct:
self.decoded = parse_construct(self._construct, do)
self.decoded = parse_construct(self._construct, do, context=context)
elif self.__class__._construct:
self.decoded = parse_construct(self.__class__._construct, do)
self.decoded = parse_construct(self.__class__._construct, do, context=context)
else:
self.decoded = self._from_bytes(do)
return self.decoded
@@ -174,27 +174,27 @@ class IE(Transcodable, metaclass=TlvMeta):
return False
@abc.abstractmethod
def to_ie(self) -> bytes:
def to_ie(self, context: dict = {}) -> bytes:
"""Convert the internal representation to entire IE including IE header."""
def to_bytes(self) -> bytes:
def to_bytes(self, context: dict = {}) -> bytes:
"""Convert the internal representation *of the value part* to binary bytes."""
if self.is_constructed():
# concatenate the encoded IE of all children to form the value part
out = b''
for c in self.children:
out += c.to_ie()
out += c.to_ie(context=context)
return out
else:
return super().to_bytes()
return super().to_bytes(context=context)
def from_bytes(self, do: bytes):
def from_bytes(self, do: bytes, context: dict = {}):
"""Parse *the value part* from binary bytes to internal representation."""
if self.nested_collection:
self.children = self.nested_collection.from_bytes(do)
self.children = self.nested_collection.from_bytes(do, context=context)
else:
self.children = []
return super().from_bytes(do)
return super().from_bytes(do, context=context)
class TLV_IE(IE):
@@ -226,15 +226,15 @@ class TLV_IE(IE):
"""Encode the length part assuming a certain binary value. Must be provided by
derived (TLV format specific) class."""
def to_ie(self):
return self.to_tlv()
def to_ie(self, context: dict = {}):
return self.to_tlv(context=context)
def to_tlv(self):
def to_tlv(self, context: dict = {}):
"""Convert the internal representation to binary TLV bytes."""
val = self.to_bytes()
val = self.to_bytes(context=context)
return self._encode_tag() + self._encode_len(val) + val
def from_tlv(self, do: bytes):
def from_tlv(self, do: bytes, context: dict = {}):
if len(do) == 0:
return {}, b''
(rawtag, remainder) = self.__class__._parse_tag_raw(do)
@@ -248,7 +248,7 @@ class TLV_IE(IE):
else:
value = do
remainder = b''
dec = self.from_bytes(value)
dec = self.from_bytes(value, context=context)
return dec, remainder
@@ -343,7 +343,7 @@ class TLV_IE_Collection(metaclass=TlvCollectionMeta):
else:
raise TypeError
def from_bytes(self, binary: bytes) -> List[TLV_IE]:
def from_bytes(self, binary: bytes, context: dict = {}) -> List[TLV_IE]:
"""Create a list of TLV_IEs from the collection based on binary input data.
Args:
binary : binary bytes of encoded data
@@ -357,6 +357,7 @@ class TLV_IE_Collection(metaclass=TlvCollectionMeta):
first = next(iter(self.members_by_tag.values()))
# iterate until no binary trailer is left
while len(remainder):
context['siblings'] = res
# obtain the tag at the start of the remainder
tag, r = first._parse_tag_raw(remainder)
if tag == None:
@@ -365,7 +366,7 @@ class TLV_IE_Collection(metaclass=TlvCollectionMeta):
cls = self.members_by_tag[tag]
# create an instance and parse accordingly
inst = cls()
dec, remainder = inst.from_tlv(remainder)
dec, remainder = inst.from_tlv(remainder, context=context)
res.append(inst)
else:
# unknown tag; create the related class on-the-fly using the same base class
@@ -376,7 +377,7 @@ class TLV_IE_Collection(metaclass=TlvCollectionMeta):
cls._to_bytes = lambda s: bytes.fromhex(s.decoded['raw'])
# create an instance and parse accordingly
inst = cls()
dec, remainder = inst.from_tlv(remainder)
dec, remainder = inst.from_tlv(remainder, context=context)
res.append(inst)
self.children = res
return res
@@ -413,17 +414,18 @@ class TLV_IE_Collection(metaclass=TlvCollectionMeta):
# self.__class__.__name__, but that is usually some meaningless auto-generated collection name.
return [x.to_dict() for x in self.children]
def to_bytes(self):
def to_bytes(self, context: dict = {}):
out = b''
context['siblings'] = self.children
for c in self.children:
out += c.to_tlv()
out += c.to_tlv(context=context)
return out
def from_tlv(self, do):
return self.from_bytes(do)
def from_tlv(self, do, context: dict = {}):
return self.from_bytes(do, context=context)
def to_tlv(self):
return self.to_bytes()
def to_tlv(self, context: dict = {}):
return self.to_bytes(context=context)
def flatten_dict_lists(inp):