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tlv: Don't require encoder/decoder methods for TLV without value 

There are instances where a TLV IE is used as just a flag, i.e.
length zero and no value part.  In those situations, it would require
a lot of boilerplate code to require the TLV_IE class definitions to
have _to_bytes/_from_bytes methods that do nothing.

So instead, add a shortcut: If we want to encode 'None', then return
b'', and if we want to decode b'' return None.

Change-Id: Ie8eb2830e8eefa81e94b8b8b157062c085aeb777
This commit is contained in:
Harald Welte 2021-10-21 10:02:10 +02:00
parent 0bc5326b76
commit 04c1302b68
1 changed files with 6 additions and 2 deletions
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8
pySim/tlv.py
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@ -80,7 +80,9 @@ class Transcodable(abc.ABC):
def to_bytes(self) -> bytes: def to_bytes(self) -> bytes:
"""Convert from internal representation to binary bytes. Store the binary result """Convert from internal representation to binary bytes. Store the binary result
in the internal state and return it.""" in the internal state and return it."""
if self._construct: if not self.decoded:
do = b''
elif self._construct:
do = self._construct.build(self.decoded, total_len=None) do = self._construct.build(self.decoded, total_len=None)
elif self.__class__._construct: elif self.__class__._construct:
do = self.__class__._construct.build(self.decoded, total_len=None) do = self.__class__._construct.build(self.decoded, total_len=None)
@ -97,7 +99,9 @@ class Transcodable(abc.ABC):
"""Convert from binary bytes to internal representation. Store the decoded result """Convert from binary bytes to internal representation. Store the decoded result
in the internal state and return it.""" in the internal state and return it."""
self.encoded = do self.encoded = do
if self._construct: if self.encoded == b'':
self.decoded = None
elif self._construct:
self.decoded = parse_construct(self._construct, do) self.decoded = parse_construct(self._construct, do)
elif self.__class__._construct: elif self.__class__._construct:
self.decoded = parse_construct(self.__class__._construct, do) self.decoded = parse_construct(self.__class__._construct, do)