3 files changed, 94 insertions, 103 deletions

diff --git a/README b/README
index 1f42487..a5dcd32 100644
--- a/README
+++ b/README
@@ -32,21 +32,21 @@ $ . glucometerutils-venv/bin/activate
 Please see the following table for the driver for each device that is known and
 supported.
 
-| Manufacturer | Model Name              | Driver             | Dependencies          |
-| ---          | ---                     | ---                | ---                   |
-| LifeScan     | OneTouch Ultra 2        | `otultra2`         | [pyserial]            |
-| LifeScan     | OneTouch Ultra Easy     | `otultraeasy`      | [pyserial]            |
-| LifeScan     | OneTouch Ultra Mini     | `otultraeasy`      | [pyserial]            |
-| LifeScan     | OneTouch Verio (USB)    | `otverio2015`      | [python-scsi]         |
-| LifeScan     | OneTouch Select Plus    | `otverio2015`      | [python-scsi]         |
-| Abbott       | FreeStyle InsuLinx†     | `fsinsulinx`       | [construct] [hidapi]‡ |
-| Abbott       | FreeStyle Libre         | `fslibre`          | [construct] [hidapi]‡ |
-| Abbott       | FreeStyle Optium        | `fsoptium`         | [pyserial]            |
-| Abbott       | FreeStyle Precision Neo | `fsprecisionneo`   | [construct] [hidapi]‡ |
-| Abbott       | FreeStyle Optium Neo    | `fsprecisionneo`   | [construct] [hidapi]‡ |
-| Abbott       | FreeStyle Optium Neo H  | `fsprecisionneo`   | [construct] [hidapi]‡ |
-| Roche        | Accu-Chek Mobile        | `accuchek_reports` |                       |
-| SD Biosensor | SD CodeFree             | `sdcodefree`       | [pyserial]            |
+| Manufacturer | Model Name              | Driver             | Dependencies           |
+| ---          | ---                     | ---                | ---                    |
+| LifeScan     | OneTouch Ultra 2        | `otultra2`         | [pyserial]             |
+| LifeScan     | OneTouch Ultra Easy     | `otultraeasy`      | [pyserial]             |
+| LifeScan     | OneTouch Ultra Mini     | `otultraeasy`      | [pyserial]             |
+| LifeScan     | OneTouch Verio (USB)    | `otverio2015`      | [python-scsi]          |
+| LifeScan     | OneTouch Select Plus    | `otverio2015`      | [python-scsi]          |
+| Abbott       | FreeStyle InsuLinx†     | `fsinsulinx`       | [construct] [hidapi]‡  |
+| Abbott       | FreeStyle Libre         | `fslibre`          | [construct] [hidapi]‡  |
+| Abbott       | FreeStyle Optium        | `fsoptium`         | [pyserial]             |
+| Abbott       | FreeStyle Precision Neo | `fsprecisionneo`   | [construct] [hidapi]‡  |
+| Abbott       | FreeStyle Optium Neo    | `fsprecisionneo`   | [construct] [hidapi]‡  |
+| Abbott       | FreeStyle Optium Neo H  | `fsprecisionneo`   | [construct] [hidapi]‡  |
+| Roche        | Accu-Chek Mobile        | `accuchek_reports` |                        |
+| SD Biosensor | SD CodeFree             | `sdcodefree`       | [construct] [pyserial] |
 
 † Untested.
 ‡ Optional dependency on Linux; required on other operating systems.
diff --git a/glucometerutils/drivers/sdcodefree.py b/glucometerutils/drivers/sdcodefree.py
index 4a375bd..2d145cc 100644
--- a/glucometerutils/drivers/sdcodefree.py
+++ b/glucometerutils/drivers/sdcodefree.py
@@ -19,96 +19,83 @@ __email__ = 'flameeyes@flameeyes.eu'
 __copyright__ = 'Copyright © 2017, Diego Elio Pettenò'
 __license__ = 'MIT'
 
-import array
-import collections
+import binascii
 import datetime
+import enum
 import functools
 import logging
 import operator
-import struct
-import time
+
+import construct
 
 from glucometerutils import common
 from glucometerutils import exceptions
 from glucometerutils.support import serial
 
-_STX = 0x53    # Not really 'STX'
-_ETX = 0xAA    # Not really 'ETX'
-
-_DIR_IN = 0x20
-_DIR_OUT = 0x10
-
-_IDX_STX = 0
-_IDX_DIRECTION = 1
-_IDX_LENGTH = 2
-_IDX_CHECKSUM = -2
-_IDX_ETX = -1
+def xor_checksum(msg):
+    return functools.reduce(operator.xor, msg)
 
-_RECV_PREAMBLE = b'\x53\x20'
+class Direction(enum.Enum):
+    In = 0x20
+    Out = 0x10
+
+_PACKET = construct.Struct(
+    'stx' / construct.Const(construct.Byte, 0x53),
+    'direction' / construct.SymmetricMapping(
+        construct.Byte,
+        {e: e.value for e in Direction}),
+    'length' / construct.Rebuild(
+        construct.Byte, lambda ctx: len(ctx.message) + 2),
+    'message' / construct.Bytes(length=lambda ctx: ctx.length - 2),
+    'checksum' / construct.Checksum(
+        construct.Byte, xor_checksum, construct.this.message),
+    'etx' / construct.Const(construct.Byte, 0xAA)
+)
+
+_FIRST_MESSAGE = construct.Struct(
+    construct.Const(construct.Byte, 0x30),
+    'count' / construct.Int16ub,
+    construct.Const(construct.Byte, 0xAA)[19])
 
 _CHALLENGE_PACKET_FULL = b'\x53\x20\x04\x10\x30\x20\xAA'
-_RESPONSE_PACKET = b'\x10\x40'
-
-_DATE_SET_PACKET = b'\x10\x10'
+_RESPONSE_MESSAGE = b'\x10\x40'
 
-_DISCONNECT_PACKET = b'\x10\x60'
-_DISCONNECTED_PACKET = b'\x10\x70'
+_DATE_SET_MESSAGE = b'\x10\x10'
 
-_STRUCT_READINGS_COUNT = struct.Struct('>H')
+_DISCONNECT_MESSAGE = b'\x10\x60'
+_DISCONNECTED_MESSAGE = b'\x10\x70'
 
-_FETCH_PACKET = b'\x10\x60'
-
-_ReadingRecord = collections.namedtuple(
-    '_ReadingRecord',
-    ('unknown1', 'unknown2', 'year', 'month', 'day', 'hour', 'minute',
-     'value', 'meal_flag'))
-_STRUCT_READING = struct.Struct('>BBBBBBBHB')
+_FETCH_MESSAGE = b'\x10\x60'
 
 _MEAL_FLAG = {
-    0x00: common.Meal.NONE,
-    0x10: common.Meal.BEFORE,
-    0x20: common.Meal.AFTER,
+    common.Meal.NONE: 0x00,
+    common.Meal.BEFORE: 0x10,
+    common.Meal.AFTER: 0x20,
 }
 
-def parse_reading(msgdata):
-    return _ReadingRecord(*_STRUCT_READING.unpack_from(msgdata))
+_READING = construct.Struct(
+    construct.Byte[2],
+    'year' / construct.Byte,
+    'month' / construct.Byte,
+    'day' / construct.Byte,
+    'hour' / construct.Byte,
+    'minute' / construct.Byte,
+    'value' / construct.Int16ub,
+    'meal' / construct.SymmetricMapping(
+        construct.Byte, _MEAL_FLAG),
+    construct.Byte[7],
+)
 
-def xor_checksum(msg):
-    return functools.reduce(operator.xor, msg)
 
 class Device(serial.SerialDevice):
     BAUDRATE = 38400
     DEFAULT_CABLE_ID = '10c4:ea60'  # Generic cable.
     TIMEOUT = 300  # We need to wait for data from the device.
 
-    def read_packet(self):
-        preamble = self.serial_.read(3)
-        if len(preamble) != 3:
-            raise exceptione.InvalidResponse(
-                response='Expected 3 bytes, received %d' % len(preamble))
-        if preamble[0:_IDX_LENGTH] != _RECV_PREAMBLE:
-            raise exceptions.InvalidResponse(
-                response='Unexpected preamble %r' % pramble[0:_IDX_LENGTH])
-
-        msglen = preamble[_IDX_LENGTH]
-        message = self.serial_.read(msglen)
-        if len(message) != msglen:
-            raise exception.InvalidResponse(
-                response='Expected %d bytes, received %d' %
-                (msglen, len(message)))
-        if message[_IDX_ETX] != _ETX:
-            raise exception.InvalidResponse(
-                response='Unexpected end-of-transmission byte: %02x' %
-                message[_IDX_ETX])
-
-        # Calculate the checksum up until before the checksum itself.
-        msgdata = message[:_IDX_CHECKSUM]
-
-        cksum = xor_checksum(msgdata)
-        if cksum != message[_IDX_CHECKSUM]:
-            raise exception.InvalidChecksum(message[_IDX_CHECKSUM], cksum)
-
-        return msgdata
+    def read_message(self):
+        pkt = _PACKET.parse_stream(self.serial_)
+        logging.debug('received packet: %r', pkt)
+        return pkt.message
 
     def wait_and_ready(self):
         challenge = self.serial_.read(1)
@@ -116,6 +103,7 @@ class Device(serial.SerialDevice):
         # The first packet read may have a prefixed zero, it might be a bug in
         # the cp210x driver or device, but discard it if found.
         if challenge == b'\0':
+            logging.debug('spurious null byte received')
             challege = self.serial_.read(1)
             if challenge != b'\x53':
                 raise exceptions.ConnectionFailed(
@@ -127,30 +115,33 @@ class Device(serial.SerialDevice):
             raise exceptions.ConnectionFailed(
                 message='Unexpected challenge %r' % challenge)
 
-        self.send_packet(_RESPONSE_PACKET)
+        logging.debug(
+            'challenge packet received: %s', binascii.hexlify(challenge))
+
+        self.send_message(_RESPONSE_MESSAGE)
 
         # The first packet only contains the counter of how many readings are
         # available.
-        first_packet = self.read_packet()
-
-        count = _STRUCT_READINGS_COUNT.unpack_from(first_packet, 1)
+        first_message = _FIRST_MESSAGE.parse(self.read_message())
+        logging.debug('received first message: %r', first_message)
 
-        return count[0]
+        return first_message.count
 
-    def send_packet(self, msgdata):
-        packet = array.array('B')
-        packet.extend((_STX, _DIR_OUT, len(msgdata)+2))
-        packet.extend(msgdata)
-        packet.extend((xor_checksum(msgdata), _ETX))
-        self.serial_.write(packet.tobytes())
+    def send_message(self, message):
+        pkt = _PACKET.build({
+            'message': message,
+            'direction': Direction.Out
+        })
+        logging.debug('sending packet: %s', binascii.hexlify(pkt))
+        self.serial_.write(pkt)
 
     def connect(self):
         print("Please connect and turn on the device.")
 
     def disconnect(self):
-        self.send_packet(_DISCONNECT_PACKET)
-        response = self.read_packet()
-        if response != _DISCONNECTED_PACKET:
+        self.send_message(_DISCONNECT_MESSAGE)
+        response = self.read_message()
+        if response != _DISCONNECTED_MESSAGE:
             raise exceptions.InvalidResponse(response=response)
 
     def get_meter_info(self):
@@ -175,9 +166,9 @@ class Device(serial.SerialDevice):
         # Ignore the readings count.
         self.wait_and_ready()
 
-        self.send_packet(setdatecmd)
-        response = self.read_packet()
-        if response != _DATE_SET_PACKET:
+        self.send_message(setdatecmd)
+        response = self.read_message()
+        if response != _DATE_SET_MESSAGE:
             raise exceptions.InvalidResponse(response=response)
 
         # The date we return should only include up to minute, unfortunately.
@@ -185,19 +176,19 @@ class Device(serial.SerialDevice):
                                  date.hour, date.minute)
 
     def zero_log(self):
-        raise NotmplementedError
+        raise NotImplementedError
 
     def get_readings(self):
         count = self.wait_and_ready()
 
         for _ in range(count):
-            self.send_packet(_FETCH_PACKET)
-            rpkt = self.read_packet()
+            self.send_message(_FETCH_MESSAGE)
+            message = self.read_message()
 
-            r = parse_reading(rpkt)
-            meal = _MEAL_FLAG[r.meal_flag]
+            r = _READING.parse(message)
+            logging.debug('received reading: %r', r)
 
             yield common.GlucoseReading(
                 datetime.datetime(
                     2000 + r.year, r.month, r.day, r.hour, r.minute),
-                r.value, meal=meal)
+                r.value, meal=r.meal)
diff --git a/setup.py b/setup.py
index c49745a..a9b7c18 100644
--- a/setup.py
+++ b/setup.py
@@ -56,7 +56,7 @@ setup(
         'fsoptium': ['pyserial'],
         'fsprecisionneo': ['construct', 'hidapi'],
         'accucheck_reports': [],
-        'sdcodefree': ['pyserial'],
+        'sdcodefree': ['construct', 'pyserial'],
     },
     entry_points = {
         'console_scripts': [