Add codecs for EF_SPN and GSM strings via construct
This will replace the hand-crafted codec for EF_SPN
by a struct definition using the construct library.
Old encoders are updated and kept for API compatibility
but are not used internally anymore.
New data structures:
* Rpad(Adapter): Right-padded bytestring (0xff, adjustable)
* GsmStringAdapter(Adapter): Codec for "SMS default 7-bit
coded alphabet as defined int TS 23.038" using
the gsm0338 library.
* GsmString(n): Convenient wrapper of both above
Adjustments:
* utils: update+deprecate old dec_spn(), enc_spn()
* remove refs to deprecated functions
Change-Id: Ia1d3a3835933bac0002b7c52511481dd8094b994
diff --git a/pySim/construct.py b/pySim/construct.py
index b0f03b7..a903305 100644
--- a/pySim/construct.py
+++ b/pySim/construct.py
@@ -1,5 +1,6 @@
from construct import *
from pySim.utils import b2h, h2b, swap_nibbles
+import gsm0338
"""Utility code related to the integration of the 'construct' declarative parser."""
@@ -33,6 +34,42 @@
def _encode(self, obj, context, path):
return h2b(swap_nibbles(obj))
+class Rpad(Adapter):
+ """
+ Encoder appends padding bytes (b'\\xff') up to target size.
+ Decoder removes trailing padding bytes.
+
+ Parameters:
+ subcon: Subconstruct as defined by construct library
+ pattern: set padding pattern (default: b'\\xff')
+ """
+
+ def __init__(self, subcon, pattern=b'\xff'):
+ super().__init__(subcon)
+ self.pattern = pattern
+
+ def _decode(self, obj, context, path):
+ return obj.rstrip(self.pattern)
+
+ def _encode(self, obj, context, path):
+ if len(obj) > self.sizeof():
+ raise SizeofError("Input ({}) exceeds target size ({})".format(len(obj), self.sizeof()))
+ return obj + self.pattern * (self.sizeof() - len(obj))
+
+class GsmStringAdapter(Adapter):
+ """Convert GSM 03.38 encoded bytes to a string."""
+
+ def __init__(self, subcon, codec='gsm03.38', err='strict'):
+ super().__init__(subcon)
+ self.codec = codec
+ self.err = err
+
+ def _decode(self, obj, context, path):
+ return obj.decode(self.codec)
+
+ def _encode(self, obj, context, path):
+ return obj.encode(self.codec, self.err)
+
def filter_dict(d, exclude_prefix='_'):
"""filter the input dict to ensure no keys starting with 'exclude_prefix' remain."""
res = {}
@@ -88,3 +125,17 @@
n (Integer): Number of bytes (default: 1)
'''
return Default(Bytes(n), __RFU_VALUE)
+
+def GsmString(n):
+ '''
+ GSM 03.38 encoded byte string of fixed length n.
+ Encoder appends padding bytes (b'\\xff') to maintain
+ length. Decoder removes those trailing bytes.
+
+ Exceptions are raised for invalid characters
+ and length excess.
+
+ Parameters:
+ n (Integer): Fixed length of the encoded byte string
+ '''
+ return GsmStringAdapter(Rpad(Bytes(n), pattern=b'\xff'), codec='gsm03.38')