5 files changed, 139 insertions, 29 deletions

diff --git a/glucometerutils/drivers/lifescan_common.py b/glucometerutils/drivers/lifescan_common.py
new file mode 100644
index 0000000..ac25d22
--- /dev/null
+++ b/glucometerutils/drivers/lifescan_common.py
@@ -0,0 +1,70 @@
+# -*- coding: utf-8 -*-
+"""Common utility functions for LifeScan meters."""
+
+__author__ = 'Diego Elio Pettenò'
+__email__ = 'flameeyes@flameeyes.eu'
+__copyright__ = 'Copyright © 2013, Diego Elio Pettenò'
+__license__ = 'GPL v3 or later'
+
+import ctypes
+
+from glucometerutils import exceptions
+
+
+class MissingChecksum(exceptions.InvalidResponse):
+  """The response misses the expected 4-digits checksum."""
+  def __init__(self, response):
+    self.message = 'Response is missing checksum: %s' % response
+
+
+class InvalidChecksum(exceptions.InvalidResponse):
+  def __init__(self, expected, gotten):
+    self.message = (
+      'Response checksum not matching: %04x expected, %04x gotten' %
+      (expected, gotten))
+
+
+class InvalidSerialNumber(exceptions.Error):
+  """The serial number is not as expected."""
+  def __init__(self, serial_number):
+    self.message = 'Serial number %s is invalid.' % serial_number
+
+
+def calculate_checksum(bytestring):
+  """Calculate the "CRC16 Sick" style checksum for LifeScan protocols.
+
+  Args:
+    bytestring: the string of which the checksum has to be calculated.
+
+  Returns:
+    A 16-bit integer that is the checksum for the input.
+
+  Credits for this code go to Christian Navalici, who implemented it in his
+  library at https://github.com/cristianav/PyCRC/ .
+  """
+  crcValue = 0x0000
+  prev_c = 0x0000
+
+  for idx, c in enumerate(bytestring):
+    short_c  =  0x00ff & c
+
+    idx_previous = idx - 1
+    short_p  = ( 0x00ff & prev_c) << 8;
+
+    if ( crcValue & 0x8000 ):
+      crcValue = ctypes.c_ushort(crcValue << 1).value ^ 0x8005
+    else:
+      crcValue = ctypes.c_ushort(crcValue << 1).value
+
+    crcValue &= 0xffff
+    crcValue ^= ( short_c | short_p )
+
+    prev_c = short_c
+
+  # After processing, the one's complement of the CRC is calcluated and the
+  # two bytes of the CRC are swapped.
+  low_byte   = (crcValue & 0xff00) >> 8
+  high_byte  = (crcValue & 0x00ff) << 8
+  crcValue   = low_byte | high_byte;
+
+  return crcValue
diff --git a/glucometerutils/drivers/otultra2.py b/glucometerutils/drivers/otultra2.py
index f453dc9..ebfda8f 100644
--- a/glucometerutils/drivers/otultra2.py
+++ b/glucometerutils/drivers/otultra2.py
@@ -13,19 +13,7 @@ import serial
 
 from glucometerutils import common
 from glucometerutils import exceptions
-
-
-class MissingChecksum(exceptions.InvalidResponse):
-  """The response misses the expected 4-digits checksum."""
-  def __init__(self, response):
-    self.response = response
-
-  def __str__(self):
-    return 'Response is missing the OT2 checksum: %s' % self.response
-
-
-class InvalidSerialNumber(exceptions.Error):
-  """The serial number is not ending with Y as expected."""
+from glucometerutils.drivers import lifescan_common
 
 
 class Device(object):
@@ -62,11 +50,22 @@ class Device(object):
     match = self._RESPONSE_MATCH.match(line)
 
     if not match:
-      raise MissingChecksum(line)
+      raise lifescan_common.MissingChecksum(line)
+
+    response, checksum_string = match.groups()
+
+    try:
+      checksum_given = int(checksum_string, 16)
+      checksum_calculated = lifescan_common.calculate_checksum(
+        bytes(response, 'ascii'))
 
-    response, checksum = match.groups()
+      if checksum_given != checksum_calculated:
+        raise lifescan_common.InvalidChecksum(checksum_given,
+                                              checksum_calculated)
+    except ValueError:
+      raise lifescan_common.InvalidChecksum(checksum_given,
+                                            None)
 
-    # TODO(flameeyes) check that the checksum is actually valid
     return response
 
   def _send_oneliner_command(self, cmd):
@@ -122,7 +121,7 @@ class Device(object):
     # 'Y' at the far right of the serial number is the indication of a OneTouch
     # Ultra2 device, as per specs.
     if serial_number[-1] != 'Y':
-      raise InvalidSerialNumber('Serial number %s is invalid.' % serial_number)
+      raise lifescan_common.InvalidSerialNumber(serial_number)
 
     return serial_number
 
diff --git a/glucometerutils/exceptions.py b/glucometerutils/exceptions.py
index 00c9e91..1acf9a4 100644
--- a/glucometerutils/exceptions.py
+++ b/glucometerutils/exceptions.py
@@ -9,22 +9,19 @@ __license__ = 'GPL v3 or later'
 class Error(Exception):
   """Base class for the errors."""
 
+  def __str__(self):
+    return self.message
+
 
 class InvalidResponse(Error):
   """The response received from the meter was not understood"""
 
   def __init__(self, response):
-    self.response = response
-
-  def __str__(self):
-    return 'Invalid response received:\n%s' % self.response
+    self.message = 'Invalid response received:\n%s' % response
 
 
 class InvalidGlucoseUnit(Error):
   """Unable to parse the given glucose unit"""
 
   def __init__(self, unit):
-    self.unit = unit
-
-  def __str__(self):
-    return 'Invalid glucose unit received:\n%s' % self.unit
+    self.message = 'Invalid glucose unit received:\n%s' % unit
diff --git a/test/test_lifescan.py b/test/test_lifescan.py
new file mode 100644
index 0000000..774567d
--- /dev/null
+++ b/test/test_lifescan.py
@@ -0,0 +1,29 @@
+# -*- coding: utf-8 -*-
+"""Tests for the LifeScan Common functions."""
+
+__author__ = 'Diego Elio Pettenò'
+__email__ = 'flameeyes@flameeyes.eu'
+__copyright__ = 'Copyright © 2013, Diego Elio Pettenò'
+__license__ = 'GPL v3 or later'
+
+import os
+import sys
+import unittest
+
+sys.path.append(os.path.dirname(os.path.dirname(os.path.abspath(__file__))))
+
+from glucometerutils import common
+from glucometerutils.drivers import lifescan_common
+from glucometerutils import exceptions
+
+
+class TestOTUltra2(unittest.TestCase):
+  def testChecksum(self):
+    checksum = lifescan_common.calculate_checksum(bytes('T', 'ascii'))
+    self.assertEqual(0x5400, checksum)
+
+    checksum = lifescan_common.calculate_checksum(bytes('TestString', 'ascii'))
+    self.assertEqual(0x0643, checksum)
+
+if __name__ == '__main__':
+    unittest.main()
diff --git a/test/test_otultra2.py b/test/test_otultra2.py
index ba577c3..6ffea83 100644
--- a/test/test_otultra2.py
+++ b/test/test_otultra2.py
@@ -15,6 +15,7 @@ import mock
 sys.path.append(os.path.dirname(os.path.dirname(os.path.abspath(__file__))))
 
 from glucometerutils import common
+from glucometerutils.drivers import lifescan_common
 from glucometerutils.drivers import otultra2
 from glucometerutils import exceptions
 
@@ -30,7 +31,7 @@ class TestOTUltra2(unittest.TestCase):
   def testMissingChecksum(self):
     self.mock_readline.return_value = bytes('INVALID', 'ascii')
 
-    self.assertRaises(otultra2.MissingChecksum,
+    self.assertRaises(lifescan_common.MissingChecksum,
                       self.device.get_serial_number)
 
   def testShortResponse(self):
@@ -40,16 +41,30 @@ class TestOTUltra2(unittest.TestCase):
                       self.device.get_serial_number)
 
   def testInvalidResponse(self):
-    self.mock_readline.return_value = bytes('% 1337\r', 'ascii')
+    self.mock_readline.return_value = bytes('% 2500\r', 'ascii')
 
     self.assertRaises(exceptions.InvalidResponse,
                       self.device.get_serial_number)
 
   def testInvalidSerialNumber(self):
     self.mock_readline.return_value = bytes(
-      '@ "12345678O" 1337\r', 'ascii')
+      '@ "12345678O" E105\r', 'ascii')
 
-    self.assertRaises(otultra2.InvalidSerialNumber,
+    self.assertRaises(lifescan_common.InvalidSerialNumber,
+                      self.device.get_serial_number)
+
+  def testInvalidChecksum(self):
+    self.mock_readline.return_value = bytes(
+      '% 1337\r', 'ascii')
+
+    self.assertRaises(lifescan_common.InvalidChecksum,
+                      self.device.get_serial_number)
+
+  def testBrokenChecksum(self):
+    self.mock_readline.return_value = bytes(
+      '% 13AZ\r', 'ascii')
+
+    self.assertRaises(lifescan_common.MissingChecksum,
                       self.device.get_serial_number)
 
 if __name__ == '__main__':