pySim-shell: Validate that argument to 'apdu' command is proper hexstr

Let's not even send anything to the card if it's not an even number
of hexadecimal digits

Change-Id: I58465244101cc1a976e5a17af2aceea1cf9f9b54

pySim-shell.py

@@ -53,7 +53,7 @@ from pySim.transport import init_reader, ApduTracer, argparse_add_reader_args, P
 from pySim.cards import card_detect, SimCardBase, UiccCardBase
 from pySim.utils import h2b, b2h, i2h, swap_nibbles, rpad, JsonEncoder, bertlv_parse_one, sw_match
 from pySim.utils import sanitize_pin_adm, tabulate_str_list, boxed_heading_str, Hexstr, dec_iccid
-from pySim.utils import is_hexstr_or_decimal
+from pySim.utils import is_hexstr_or_decimal, is_hexstr
 from pySim.card_handler import CardHandler, CardHandlerAuto
 
 from pySim.filesystem import CardDF, CardADF, CardModel, CardApplication
@@ -322,7 +322,7 @@ Online manual available at https://downloads.osmocom.org/docs/pysim/master/html/
         self.equip(card, rs)
 
     apdu_cmd_parser = argparse.ArgumentParser()
-    apdu_cmd_parser.add_argument('APDU', type=str, help='APDU as hex string')
+    apdu_cmd_parser.add_argument('APDU', type=is_hexstr, help='APDU as hex string')
     apdu_cmd_parser.add_argument('--expect-sw', help='expect a specified status word', type=str, default=None)
 
     @cmd2.with_argparser(apdu_cmd_parser)

pySim/utils.py

@@ -1478,3 +1478,12 @@ def is_hexstr_or_decimal(instr: str) -> str:
     if len(instr) & 1:
         raise ValueError('Input has un-even number of hex digits')
     return instr
+
+def is_hexstr(instr: str) -> str:
+    """Method that can be used as 'type' in argparse.add_argument() to validate the value consists of
+    an even sequence of hexadecimal digits only."""
+    if not all(c in string.hexdigits for c in instr):
+        raise ValueError('Input must be hexadecimal')
+    if len(instr) & 1:
+        raise ValueError('Input has un-even number of hex digits')
+    return instr