From 09a5fe1f8d34ee9a9f8263624a9b92a2bcd96f79 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Diego=20Elio=20Petten=C3=B2?= <flameeyes@flameeyes.eu>
Date: Thu, 28 Dec 2017 20:16:22 +0000
Subject: freestyle: replace the custom struct and bytemangling with construct.

This simplifies the code and enforces the validation within the format
documentation too.

construct can handle the full package verification, including dealing with
padding.
---
 README                               | 31 ++++++++++++++++---------------
 glucometerutils/support/freestyle.py | 19 +++++++++++--------
 setup.py                             |  6 +++---
 3 files changed, 30 insertions(+), 26 deletions(-)

diff --git a/README b/README
index a070a05..1f42487 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`       | [hidapi]‡     |
-| Abbott       | FreeStyle Libre         | `fslibre`          | [hidapi]‡     |
-| Abbott       | FreeStyle Optium        | `fsoptium`         | [pyserial]    |
-| Abbott       | FreeStyle Precision Neo | `fsprecisionneo`   | [hidapi]‡     |
-| Abbott       | FreeStyle Optium Neo    | `fsprecisionneo`   | [hidapi]‡     |
-| Abbott       | FreeStyle Optium Neo H  | `fsprecisionneo`   | [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`       | [pyserial]            |
 
 † Untested.
 ‡ Optional dependency on Linux; required on other operating systems.
@@ -60,6 +60,7 @@ If you have knowledge of a protocol of a glucometer you would have supported,
 please provide a reference, possibly by writing a specification and contribute
 it to https://github.com/Flameeyes/glucometer-protocols/.
 
+[construct]: https://construct.readthedocs.io/en/latest/
 [pyserial]: https://pythonhosted.org/pyserial/
 [python-scsi]: https://github.com/rosjat/python-scsi
 [hidapi]: https://pypi.python.org/pypi/hidapi
diff --git a/glucometerutils/support/freestyle.py b/glucometerutils/support/freestyle.py
index d722c35..7610729 100644
--- a/glucometerutils/support/freestyle.py
+++ b/glucometerutils/support/freestyle.py
@@ -15,7 +15,8 @@ import csv
 import datetime
 import logging
 import re
-import struct
+
+import construct
 
 from glucometerutils import exceptions
 from glucometerutils.support import hiddevice
@@ -24,7 +25,13 @@ from glucometerutils.support import hiddevice
 # protocol.
 _INIT_SEQUENCE = (0x04, 0x05, 0x15, 0x01)
 
-_STRUCT_PREAMBLE = struct.Struct('<BB')
+_LIFESCAN_MESSAGE = construct.Struct(
+    'hid_report' / construct.Const(construct.Byte, 0),
+    'message_type' / construct.Byte,
+    'command' / construct.Padded(
+        63,  # command can only be up to 62 bytes, but one is used for length.
+        construct.Prefixed(construct.Byte, construct.GreedyBytes)),
+)
 
 _TEXT_COMPLETION_RE = re.compile('CMD (?:OK|Fail!)')
 _TEXT_REPLY_FORMAT = re.compile(
@@ -93,12 +100,8 @@ class FreeStyleHidDevice(hiddevice.HidDevice):
           message_type: (int) The first byte sent with the report to the device.
           command: (bytes) The command to send out the device.
         """
-        cmdlen = len(command)
-        assert cmdlen <= 62
-
-        # First byte in the written buffer is the report number.
-        usb_packet = b'\x00' + _STRUCT_PREAMBLE.pack(
-            message_type, cmdlen) + command + bytes(62 - cmdlen)
+        usb_packet = _LIFESCAN_MESSAGE.build(
+            {'message_type': message_type, 'command': command})
 
         self._write(usb_packet)
 
diff --git a/setup.py b/setup.py
index 5da8086..5e65e1e 100644
--- a/setup.py
+++ b/setup.py
@@ -34,10 +34,10 @@ setup(
         'otultra2': ['pyserial'],
         'otultraeasy': ['pyserial'],
         'otverio2015': ['python-scsi'],
-        'fsinsulinx': ['hidapi'],
-        'fslibre': ['hidapi'],
+        'fsinsulinx': ['construct', 'hidapi'],
+        'fslibre': ['construct', 'hidapi'],
         'fsoptium': ['pyserial'],
-        'fsprecisionneo': ['hidapi'],
+        'fsprecisionneo': ['construct', 'hidapi'],
         'accucheck_reports': [],
         'sdcodefree': ['pyserial'],
     },
-- 
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