implement packet splitters

bumble/transport/usb.py

@@ -59,6 +59,8 @@ USB_BT_HCI_CLASS_TUPLE = (
 )
 
 MAX_SCO_PACKET_SIZE = 1024
+MAX_SCO_IN_PACKETS = 128
+NUMBER_OF_SCO_IN_TRANSFERS = 2
 
 
 # -----------------------------------------------------------------------------
@@ -388,20 +390,35 @@ class UsbPacketSink:
 READ_SIZE = 4096
 
 
-class ScoAccumulator:
-    def __init__(self, emit: Callable[[bytes], Any]) -> None:
+class PacketSplitter:
+    """Splitter than can parse a byte stream and extract packets that consist of a
+    header and a body, where the header includes an n-byte 'length' field at a
+    certain offset.
+    Extracted packets are emitted by calling a function passed to the constructor,
+    with the full packet (header + body) as argument.
+    """
+
+    def __init__(
+        self, length_offset: int, length_size: int, emit: Callable[[bytes], Any]
+    ) -> None:
         self.emit = emit
         self.packet = b''
+        self.length_offset = length_offset
+        self.length_size = length_size
+        self.header_size = length_offset + length_size
 
     def feed(self, data: bytes) -> None:
         while data:
-            # Accumulate until we have a complete 3-byte header
-            if (bytes_needed := 3 - len(self.packet)) > 0:
+            # Accumulate until we have a complete header
+            if (bytes_needed := self.header_size - len(self.packet)) > 0:
                 self.packet += data[:bytes_needed]
                 data = data[bytes_needed:]
                 continue
 
-            packet_length = 3 + self.packet[2]
+            packet_length = self.header_size + int.from_bytes(
+                self.packet[self.length_offset : self.length_offset + self.length_size],
+                'little',
+            )
             bytes_needed = packet_length - len(self.packet)
             self.packet += data[:bytes_needed]
             data = data[bytes_needed:]
@@ -411,6 +428,24 @@ class ScoAccumulator:
                 self.packet = b''
 
 
+class ScoPacketSplitter(PacketSplitter):
+    def __init__(self, emit: Callable[[bytes], Any]) -> None:
+        # The length field is 1 byte at offset 2 in the HCI SCO packet header
+        super().__init__(length_offset=2, length_size=1, emit=emit)
+
+
+class EventPacketSplitter(PacketSplitter):
+    def __init__(self, emit: Callable[[bytes], Any]) -> None:
+        # The length field is 1 byte at offset 1 in the HCI Event packet header
+        super().__init__(length_offset=1, length_size=1, emit=emit)
+
+
+class AclPacketSplitter(PacketSplitter):
+    def __init__(self, emit: Callable[[bytes], Any]) -> None:
+        # The length field is 2 bytes at offset 2 in the HCI ACL packet header
+        super().__init__(length_offset=2, length_size=2, emit=emit)
+
+
 class UsbPacketSource(asyncio.Protocol, BaseSource):
     def __init__(self, device, metadata, interrupt_in, bulk_in, isochronous_in):
         super().__init__()
@@ -422,9 +457,6 @@ class UsbPacketSource(asyncio.Protocol, BaseSource):
         self.bulk_in_transfer = None
         self.isochronous_in = isochronous_in
         self.isochronous_in_transfer = None
-        self.isochronous_accumulator = ScoAccumulator(
-            lambda packet: self.queue_packet(hci.HCI_SYNCHRONOUS_DATA_PACKET, packet)
-        )
         self.loop = asyncio.get_running_loop()
         self.queue = asyncio.Queue()
         self.dequeue_task = None
@@ -433,6 +465,19 @@ class UsbPacketSource(asyncio.Protocol, BaseSource):
             hci.HCI_ACL_DATA_PACKET: asyncio.Event(),
             hci.HCI_SYNCHRONOUS_DATA_PACKET: asyncio.Event(),
         }
+        self.splitters = {
+            hci.HCI_EVENT_PACKET: EventPacketSplitter(
+                lambda packet: self.queue_packet(hci.HCI_EVENT_PACKET, packet)
+            ),
+            hci.HCI_ACL_DATA_PACKET: AclPacketSplitter(
+                lambda packet: self.queue_packet(hci.HCI_ACL_DATA_PACKET, packet)
+            ),
+            hci.HCI_SYNCHRONOUS_DATA_PACKET: ScoPacketSplitter(
+                lambda packet: self.queue_packet(
+                    hci.HCI_SYNCHRONOUS_DATA_PACKET, packet
+                )
+            ),
+        }
         self.closed = False
         self.lock = threading.Lock()
 
@@ -457,10 +502,12 @@ class UsbPacketSource(asyncio.Protocol, BaseSource):
         self.bulk_in_transfer.submit()
 
         if self.isochronous_in is not None:
-            self.isochronous_in_transfer = self.device.getTransfer(iso_packets=16)
+            self.isochronous_in_transfer = self.device.getTransfer(
+                iso_packets=MAX_SCO_IN_PACKETS
+            )
             self.isochronous_in_transfer.setIsochronous(
                 self.isochronous_in.getAddress(),
-                16 * self.isochronous_in.getMaxPacketSize(),
+                MAX_SCO_IN_PACKETS * self.isochronous_in.getMaxPacketSize(),
                 callback=self.transfer_callback,
                 user_data=hci.HCI_SYNCHRONOUS_DATA_PACKET,
             )
@@ -490,6 +537,8 @@ class UsbPacketSource(asyncio.Protocol, BaseSource):
             with self.lock:
                 if self.closed:
                     logger.debug("packet source closed, discarding transfer")
+                elif (splitter := self.splitters.get(packet_type)) is None:
+                    logger.warning(f'no splitter for packet type {packet_type}')
                 else:
                     if packet_type == hci.HCI_SYNCHRONOUS_DATA_PACKET:
                         for iso_status, iso_buffer in transfer.iterISO():
@@ -503,11 +552,10 @@ class UsbPacketSource(asyncio.Protocol, BaseSource):
                                 len(iso_buffer),
                                 iso_buffer.hex(),
                             )
-                            self.isochronous_accumulator.feed(iso_buffer)
+                            splitter.feed(iso_buffer)
                     else:
-                        self.queue_packet(
-                            packet_type,
-                            transfer.getBuffer()[: transfer.getActualLength()],
+                        splitter.feed(
+                            transfer.getBuffer()[: transfer.getActualLength()]
                         )
 
                     # Re-submit the transfer so we can receive more data