Add support for Freestyle Libre 3

The Libre 3 reports results in a different way:
* The history reports are missing a column of unknown meaning.
* The reading reports are missing custom comments and error values.

The current workaround makes the Libre 3 results to look like the
results for earlier models and is for demonstration and documentation
purposes only. A better implementation would abstract the difference in
reporting format into the drivers for each device.

glucometerutils/drivers/fslibre3.py

@@ -0,0 +1,48 @@
+# -*- coding: utf-8 -*-
+#
+# SPDX-FileCopyrightText: © 2023 The glucometerutils Authors
+# SPDX-License-Identifier: MIT
+"""Driver for FreeStyle Libre 3 devices.
+
+Supported features:
+    The same as the fslibre driver.
+
+Expected device path: /dev/hidraw9 or similar HID device. Optional when using
+HIDAPI.
+
+This driver is a shim on top of the fslibre driver, forcing encryption to be
+enabled for the session and normalizing the returned records.
+
+Further information on the device protocol can be found at
+
+https://protocols.glucometers.tech/abbott/freestyle-libre
+https://protocols.glucometers.tech/abbott/freestyle-libre-2
+
+"""
+
+from collections.abc import Sequence
+from typing import Optional
+
+from glucometerutils.support import freestyle_libre
+
+
+class Device(freestyle_libre.LibreDevice):
+    _MODEL_NAME = "FreeStyle Libre 3"
+
+    def __init__(self, device_path: Optional[str]) -> None:
+        super().__init__(0x3960, device_path, encoding="utf-8", encrypted=True)
+
+    @staticmethod
+    def _normalize_history_record(record: Sequence[str]) -> Sequence[str]:
+        """Overridden function as one of the unknown columns is missing."""
+        record.insert(10, "0")
+        return record
+
+    @staticmethod
+    def _normalize_result_record(record: Sequence[str]) -> Sequence[str]:
+        """Overridden function as error values and custom comments are missing."""
+        record.insert(19, "0")
+        record.insert(28, 0)
+        if len(record) > 29:
+            record = record[:29] + 6*["\"\""] + record[29:]
+        return record

glucometerutils/support/freestyle_libre.py

@@ -203,6 +203,16 @@ class LibreDevice(freestyle.FreeStyleHidDevice):
 
     _MODEL_NAME: str
 
+    @staticmethod
+    def _normalize_history_record(record: Sequence[str]) -> Sequence[str]:
+        """Normalize a history record to the base column layout."""
+        return record
+
+    @staticmethod
+    def _normalize_result_record(record: Sequence[str]) -> Sequence[str]:
+        """Normalize a result record to the base column layout."""
+        return record
+
     def get_meter_info(self) -> common.MeterInfo:
         """Return the device information in structured form."""
         return common.MeterInfo(
@@ -231,6 +241,7 @@ def get_readings(self) -> Generator[common.AnyReading, None, None]:
         # First of all get the usually longer list of sensor readings, and
         # convert them to Readings objects.
         for record in self._session.query_multirecord(b"$history?"):
+            record = self._normalize_history_record(record)
             parsed_record = _parse_record(record, _HISTORY_ENTRY_MAP)
 
             if not parsed_record or parsed_record["errors"] != 0:
@@ -248,6 +259,7 @@ def get_readings(self) -> Generator[common.AnyReading, None, None]:
         # Then get the results of explicit scans and blood tests (and other
         # events).
         for record in self._session.query_multirecord(b"$arresult?"):
+            record = self._normalize_result_record(record)
             logging.debug(f"Retrieved arresult: {record!r}")
             reading = _parse_arresult(record)
             if reading: