commands: add ".." notation to expand hexstrings

When updating files and records there are sometimes huge portions that
are just 0xff. Mostly this is at the end of a file or record that is not
completely used. Lets add a notation to tell PySim-shell how to fill
those sections.

Change-Id: Iedd7887bf7d706878f4a3beca8dbea456404610b

pySim/commands.py

@@ -23,7 +23,7 @@
 
 from construct import *
 from pySim.construct import LV
-from pySim.utils import rpad, b2h, h2b, sw_match, bertlv_encode_len, Hexstr, h2i, str_sanitize
+from pySim.utils import rpad, b2h, h2b, sw_match, bertlv_encode_len, Hexstr, h2i, str_sanitize, expand_hex
 from pySim.exceptions import SwMatchError
 
 
@@ -190,6 +190,10 @@ class SimCardCommands(object):
                 offset : byte offset in file from which to start writing
                 verify : Whether or not to verify data after write
         """
+
+        file_len = self.binary_size(ef)
+        data = expand_hex(data, file_len)
+
         data_length = len(data) // 2
 
         # Save write cycles by reading+comparing before write
@@ -255,16 +259,17 @@ class SimCardCommands(object):
                 verify : verify data by re-reading the record
                 conserve : read record and compare it with data, skip write on match
         """
+
         res = self.select_path(ef)
+        rec_length = self.__record_len(res)
+        data = expand_hex(data, rec_length)
 
         if force_len:
             # enforce the record length by the actual length of the given data input
             rec_length = len(data) // 2
         else:
-            # determine the record length from the select response of the file and pad
-            # the input data with 0xFF if necessary. In cases where the input data
-            # exceed we throw an exception.
-            rec_length = self.__record_len(res)
+            # make sure the input data is padded to the record length using 0xFF.
+            # In cases where the input data exceed we throw an exception.
             if (len(data) // 2 > rec_length):
                 raise ValueError('Data length exceeds record length (expected max %d, got %d)' % (
                     rec_length, len(data) // 2))

pySim/utils.py

@@ -1225,6 +1225,60 @@ def auto_int(x):
     return int(x, 0)
 
 
+def expand_hex(hexstring, length):
+    """Expand a given hexstring to a specified length by replacing "." or ".."
+       with a filler that is derived from the neighboring nibbles respective
+       bytes. Usually this will be the nibble respective byte before "." or
+       "..", execpt when the string begins with "." or "..", then the nibble
+       respective byte after "." or ".." is used.". In case the string cannot
+       be expanded for some reason, the input string is returned unmodified.
+
+    Args:
+            hexstring : hexstring to expand
+            length : desired length of the resulting hexstring.
+    Returns:
+            expanded hexstring
+    """
+
+    # expand digit aligned
+    if hexstring.count(".") == 1:
+        pos = hexstring.index(".")
+        if pos > 0:
+            filler = hexstring[pos - 1]
+        else:
+            filler = hexstring[pos + 1]
+
+        missing = length * 2 - (len(hexstring) - 1)
+        if missing <= 0:
+            return hexstring
+
+        return hexstring.replace(".", filler * missing)
+
+    # expand byte aligned
+    elif hexstring.count("..") == 1:
+        if len(hexstring) % 2:
+            return hexstring
+
+        pos = hexstring.index("..")
+
+        if pos % 2:
+            return hexstring
+
+        if pos > 1:
+            filler = hexstring[pos - 2:pos]
+        else:
+            filler = hexstring[pos + 2:pos+4]
+
+        missing = length * 2 - (len(hexstring) - 2)
+        if missing <= 0:
+            return hexstring
+
+        return hexstring.replace("..", filler * (missing // 2))
+
+    # no change
+    return hexstring
+
+
 class JsonEncoder(json.JSONEncoder):
     """Extend the standard library JSONEncoder with support for more types."""