ble: implement BLEDBusSession class

Current implementation of BLESession class depends on the library bluepy
to communicate with BLE devices. This implementation has two major
issues. The first issue is no maintenance of bluepy library. It's last
commit was made in May 2021. It is no longer active and it is not likely
that its issues get resolved. The second issue is lack of asyncio
interface. pyscrlink uses websockets which uses asyncio. Dirty glue code
and locks are required to connect websockets and bluepy.

This commit avoids the issue by moving away from bluepy. Instead, use
BlueZ D-Bus API. Bluepy communicates with BlueZ kernel module via bluepy
unique user space program. Instead, pyscrlink communicate with well
maintained Blue-Z user space program, or bluetoothd, through D-Bus
protocol. To handle D-Bus protocol, use python-sdbus library [2]. It has
sub-library python-sdbus-bluez to cover BlueZ D-Bus API [3].

Using these libraries, implement a new class named BLEDBusSession. It
replaces BLESession which uses bluepy. These two classes share same
base class named Session. To allow async I/O, add a new function
async_handle_request to the Session class. Until this new implementation
get proved stable enough, keep the old BLESession. Introduce a new
command line option '-b' of scratch_link. When this option is specified,
the new class is used.

To improve code readability, implement BLEDBusSession in a new file
'ble.py'. To share scan_seconds between scratch_link.py and ble.py,
change scan_seconds from global variable to an argument of Session class
constructor. Also to share logger between scratch_link.py and ble.py,
modify the logging.getLogger() argument from __name__ to scratch_link
module name.

[1] http://www.bluez.org/bluez-5-api-introduction-and-porting-guide/
[2] https://github.com/python-sdbus/python-sdbus
[3] https://github.com/python-sdbus/python-sdbus-bluez

Signed-off-by: Shin'ichiro Kawasaki <kawasaki@juno.dti.ne.jp>

README.md

@@ -102,7 +102,7 @@ Installation
 
 5. For micro:bit, install Scratch-link hex on your device.
 
-    * Download and unzip the [micro:bit Scratch Hex file](https://downloads.scratch.mit.edu/microbit/scratch-microbit-1.1.0.hex.zip).
+    * Download and unzip the [micro:bit Scratch Hex file](https://downloads.scratch.mit.edu/microbit/scratch-microbit.hex.zip).
     * Flash the micro:bit over USB with the Scratch Hex File, you will see the
       five character name of the micro:bit scroll across the screen such as
       'zo9ev'.

pyscrlink/ble.py

@@ -34,8 +34,8 @@ class BLEDBusSession(pyscrlink.scratch_link.Session):
     connected_devices = {}
 
     class Device():
-        def __init__(self, interface, path, node_name, name, address):
-            self.interface = interface
+        def __init__(self, iface, path, node_name, name, address):
+            self.iface = iface
             self.path = path
             self.node_name = node_name
             self.name = name
@@ -95,7 +95,7 @@ class BLEDBusSession(pyscrlink.scratch_link.Session):
                     logger.debug(f"service to check: {s}")
                     given_uuid = BTUUID(s)
                     logger.debug(f"given UUID: {given_uuid} hash={given_uuid.__hash__()}")
-                    dev_uuids = await dev.interface.uuids
+                    dev_uuids = await dev.iface.uuids
                     if not dev_uuids:
                         logger.debug(f"dev UUID not available")
                         continue
@@ -122,7 +122,7 @@ class BLEDBusSession(pyscrlink.scratch_link.Session):
     async def _notify_device(self, device) -> None:
         params = { 'rssi': -80, 'name': 'Unknown' }
         try:
-            params['rssi'] = await device.interface.rssi
+            params['rssi'] = await device.iface.rssi
         except Exception:
             None
         if device.name:
@@ -149,17 +149,17 @@ class BLEDBusSession(pyscrlink.scratch_link.Session):
                 devpath = self.iface + "/" + node_name
                 if BLEDBusSession.connected_devices.get(devpath):
                     continue
-                interface = DeviceInterfaceAsync()
-                interface._connect('org.bluez', devpath, bus=self.dbus)
+                iface = DeviceInterfaceAsync()
+                iface._connect('org.bluez', devpath, bus=self.dbus)
                 try:
-                    devname = await interface.name
+                    devname = await iface.name
                 except Exception as e:
                     logger.debug(f"device {node_name} does not have name: {e}")
-                devaddr = await interface.address
-                device = self.Device(interface, devpath, node_name, devname,
+                devaddr = await iface.address
+                device = self.Device(iface, devpath, node_name, devname,
                                      devaddr)
                 if not await self._matches(device, self.discover_filters):
-                    await interface.disconnect()
+                    await iface.disconnect()
                     continue
                 self.found_devices[node_name] = device
                 await self._notify_device(device)
@@ -309,7 +309,7 @@ class BLEDBusSession(pyscrlink.scratch_link.Session):
             dev = self.found_devices[params['peripheralId']]
             try:
                 logger.debug(f"  {dev}")
-                await dev.interface.connect()
+                await dev.iface.connect()
                 res["result"] = None
                 self.device = dev
                 self.status = self.CONNECTED
@@ -362,7 +362,7 @@ class BLEDBusSession(pyscrlink.scratch_link.Session):
         dev = self.device
         logger.info(f"Disconnecting from '{dev.name}'@{dev.address}")
         self._stop_notifications()
-        await dev.interface.disconnect()
+        await dev.iface.disconnect()
         BLEDBusSession.connected_devices.pop(dev.path)
         logger.info(f"Disconnected from '{dev.name}'@{dev.address}")
         self.device = None

pyscrlink/scratch_link.py

@@ -33,17 +33,8 @@ from pyscrlink import gencert
 
 from pyscrlink import ble
 
-logLevel = logging.INFO
-
 # for logging
 logger = logging.getLogger('pyscrlink.scratch_link')
-formatter = logging.Formatter(fmt='%(asctime)s %(message)s')
-handler = logging.StreamHandler()
-handler.setLevel(logLevel)
-handler.setFormatter(formatter)
-logger.setLevel(logLevel)
-logger.addHandler(handler)
-logger.propagate = False
 
 HOSTNAME="device-manager.scratch.mit.edu"
 scan_seconds=10.0
@@ -597,14 +588,24 @@ def main():
     parser.add_argument('-b', '--dbus', action='store_true',
                         help='use DBus backend for BLE devices')
     args = parser.parse_args()
+
+    logLevel = logging.INFO
     if args.debug:
-        print("Print debug messages")
         logLevel = logging.DEBUG
-        handler.setLevel(logLevel)
-        logger.setLevel(logLevel)
+
+    formatter = logging.Formatter(fmt='%(asctime)s %(message)s')
+    handler = logging.StreamHandler()
+    handler.setLevel(logLevel)
+    handler.setFormatter(formatter)
+    logger.setLevel(logLevel)
+    logger.addHandler(handler)
+    logger.propagate = False
+
     scan_seconds = args.scan_seconds
     scan_retry = args.scan_retry
     dbus = args.dbus
+    if args.debug:
+        logger.debug("Print debug messages")
     logger.debug(f"set scan_seconds: {scan_seconds}")
     logger.debug(f"set scan_retry: {scan_retry}")