Fix broken class matching on receive

Restructured match_prefixes to correctly match sequence number field
Added insurance that sequence number comes first to do so
Also caught the (macOS) case where adapter has no address (WIP)
Fixes adafruit#15

Author: alexwhittemore

adafruit_ble_broadcastnet.py

@@ -61,13 +61,16 @@ def broadcast(measurement, *, broadcast_time=0.1, extended=False):
 if not hasattr(os, "environ") or (
     "GITHUB_ACTION" not in os.environ and "READTHEDOCS" not in os.environ
 ):
-    device_address = "{:02x}{:02x}{:02x}{:02x}{:02x}{:02x}".format(  # pylint: disable=invalid-name
-        *reversed(
-            list(
-                _ble._adapter.address.address_bytes  # pylint: disable=protected-access
+    if _ble._adapter.address:
+        device_address = "{:02x}{:02x}{:02x}{:02x}{:02x}{:02x}".format(  # pylint: disable=invalid-name
+            *reversed(
+                list(
+                    _ble._adapter.address.address_bytes  # pylint: disable=protected-access
+                )
             )
         )
-    )
+    else:
+        device_address = "000000000000"
     """Device address as a string."""
 
 _MANUFACTURING_DATA_ADT = const(0xFF)
@@ -79,7 +82,8 @@ class AdafruitSensorMeasurement(Advertisement):
 
     # This prefix matches all
     match_prefixes = (
-        struct.pack("<BBH", 3, _MANUFACTURING_DATA_ADT, _ADAFRUIT_COMPANY_ID),
+        # Matches the sequence number field header (length+ID)
+        struct.pack("<BHBH", _MANUFACTURING_DATA_ADT, _ADAFRUIT_COMPANY_ID, 0x03, 0x0003),
     )
 
     manufacturer_data = LazyObjectField(
@@ -174,6 +178,13 @@ def __str__(self):
                 if value is not None:
                     parts.append("{}={}".format(attr, str(value)))
         return "<{} {} >".format(self.__class__.__name__, " ".join(parts))
+    
+    def __bytes__(self):
+        """The raw packet bytes."""
+        # Must reorder the ManufacturerData contents so the sequence number field is always first.
+        # Necessary to ensure that match_prefixes works right to reconstruct on the receiver.
+        self.data_dict[255].data.move_to_end(3, last=False)
+        return super().__bytes__()
 
     def split(self, max_packet_size=31):
         """Split the measurement into multiple measurements with the given max_packet_size. Yields

examples/ble_broadcastnet_scan_test.py

@@ -0,0 +1,14 @@
+"""This example merely scans for broadcastnet packets as a quick check that something is sending them."""
+
+from adafruit_ble.advertising.standard import ManufacturerDataField
+import adafruit_ble
+import adafruit_ble_broadcastnet
+
+ble = adafruit_ble.BLERadio()
+
+print("scanning")
+# By providing Advertisement as well we include everything, not just specific advertisements.
+for advert in ble.start_scan(
+    adafruit_ble_broadcastnet.AdafruitSensorMeasurement, interval=0.5
+):
+    print(advert)