3 files changed, 90 insertions, 36 deletions

diff --git a/glucometerutils/exceptions.py b/glucometerutils/exceptions.py
index 52c4e94..e1d9200 100644
--- a/glucometerutils/exceptions.py
+++ b/glucometerutils/exceptions.py
@@ -27,6 +27,13 @@ class ConnectionFailed(Error):
     self.message = message
 
 
+class CommandError(Error):
+  """It was not possible to send a command to the device."""
+
+  def __init__(self, message="Unable to send command to device."):
+    self.message = message
+
+
 class InvalidResponse(Error):
   """The response received from the meter was not understood"""
 
diff --git a/glucometerutils/support/freestyle.py b/glucometerutils/support/freestyle.py
index 737eda1..0e71c03 100644
--- a/glucometerutils/support/freestyle.py
+++ b/glucometerutils/support/freestyle.py
@@ -13,11 +13,11 @@ __license__ = 'MIT'
 
 import csv
 import datetime
-import os.path
 import re
 import struct
 
 from glucometerutils import exceptions
+from glucometerutils.support import hiddevice
 
 # Sequence of initialization messages sent to the device to establish HID
 # protocol.
@@ -54,7 +54,7 @@ def _verify_checksum(message, expected_checksum_hex):
         raise exceptions.InvalidChecksum(expected_checksum, calculated_checksum)
 
 
-class FreeStyleHidDevice(object):
+class FreeStyleHidDevice(hiddevice.HidDevice):
     """Base class implementing the FreeStyle HID common protocol.
 
     This class implements opening, initializing the connection and sending
@@ -72,37 +72,6 @@ class FreeStyleHidDevice(object):
     USB_VENDOR_ID = 0x1a61  # Abbott Diabetes Care
     USB_PRODUCT_ID = None
 
-    def __init__(self, device):
-        # If we do not know for sure the device ID, rely on the user providing a
-        # device path.
-        if self.USB_PRODUCT_ID is None and not device:
-            raise exceptions.CommandLineError(
-                '--device parameter is required, should point to /dev/hidraw '
-                'for the meter')
-
-        # If the user passed a device path that does not exist, raise an error.
-        if device and not os.path.exists(device):
-            raise exceptions.ConnectionFailed(
-                message='Path %s does not exist.' % device)
-
-        # If the user passed a device, try opening it. Note that I have had no
-        # success on actually opening the /dev/hidraw path but that's a
-        # different problem.
-        try:
-            if device:
-                self.handle_ = open(device, 'w+b')
-            else:
-                try:
-                    import hid
-                except ImportError:
-                    raise exceptions.ConnectionFailed(
-                        message='Missing requied "hidapi" module.')
-                self.handle_ = hid.device()
-                self.handle_.open(self.USB_VENDOR_ID, self.USB_PRODUCT_ID)
-        except OSError:
-            raise exceptions.ConnectionFailed(
-                message='Unable to connect to meter.')
-
     def connect(self):
         """Open connection to the device, starting the knocking sequence."""
         for message in _INIT_SEQUENCE:
@@ -130,12 +99,11 @@ class FreeStyleHidDevice(object):
         usb_packet = b'\x00' + _STRUCT_PREAMBLE.pack(
             message_type, cmdlen) + command + bytes(62 - cmdlen)
 
-        if self.handle_.write(usb_packet) < 0:
-            raise exceptions.InvalidResponse()
+        self._write(usb_packet)
 
     def _read_response(self):
         """Read the response from the device and extracts it."""
-        usb_packet = self.handle_.read(64)
+        usb_packet = self._read()
 
         assert usb_packet
         message_type = usb_packet[0]
diff --git a/glucometerutils/support/hiddevice.py b/glucometerutils/support/hiddevice.py
new file mode 100644
index 0000000..a3f2776
--- /dev/null
+++ b/glucometerutils/support/hiddevice.py
@@ -0,0 +1,79 @@
+"""Common routines and base driver class for HID-based meters.
+"""
+
+__author__ = 'Diego Elio Pettenò'
+__email__ = 'flameeyes@flameeyes.eu'
+__copyright__ = 'Copyright © 2017, Diego Elio Pettenò'
+__license__ = 'MIT'
+
+import logging
+import os
+
+from glucometerutils import exceptions
+
+
+class HidDevice(object):
+    """A device speaking USB HID protocol driver base.
+
+    This class does not implement an actual driver by itself, but provides an
+    easier access to the boilerplate code required for speaking USB HID.
+
+    This helper wraps around an optional dependency on hidapi library: if
+    present the driver will auto-detect the device, if not the device path needs
+    to be provided and should point to a device implementing Linux's hidraw
+    interface.
+
+    The following constants can be set by the actual drivers:
+
+      USB_VENDOR_ID: (int) USB vendor ID for the device.
+      USB_PRODUCT_ID: (int) USB product ID for the device.
+
+    If the VID/PID pair is not provided, the driver will require a device path
+    to be used.
+    """
+
+    USB_VENDOR_ID = None
+    USB_PRODUCT_ID = None
+
+    def __init__(self, device):
+        if None in (self.USB_VENDOR_ID, self.USB_PRODUCT_ID) and not device:
+            raise exceptions.CommandLineError(
+                '--device parameter is required, should point to a /dev/hidraw '
+                'device node representing the meter.')
+
+        # If the user passed a device path that does not exist, raise an
+        # error. This is to avoid writing to a file instead of to a device node.
+        if device and not os.path.exists(device):
+            raise exceptions.ConnectionFailed(
+                message='Path %s does not exist.' % device)
+
+        # If the user passed a device, try opening it.
+        if device:
+            self.handle_ = open(device, 'w+b')
+        else:
+            logging.info(
+                'No --device parameter provided, using hidapi library.')
+            try:
+                import hid
+                self.handle_ = hid.device()
+                self.handle_.open(self.USB_VENDOR_ID, self.USB_PRODUCT_ID)
+            except ImportError:
+                raise exceptions.ConnectionFailed(
+                    message='Missing requied "hidapi" module.')
+            except OSError as e:
+                raise exceptions.ConnectionFailed(
+                    message='Unable to connect to meter: %s.' % e)
+
+    def _write(self, report):
+        """Writes a report to the HID handle."""
+
+        if self.handle_.write(report) < 0:
+            raise exceptions.CommandError()
+
+    def _read(self, size=64):
+        """Read a report from the HID handle.
+
+        This is important as it handles the one incompatible interface between
+        hidraw devices and hidapi handles.
+        """
+        return bytes(self.handle_.read(size))