Fix HCI event filter for events >= 32 (LE Meta Event) #51
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The setEvent() method always set bits in eventMask.0, even for events with codes >= 32. The HCI filter structure uses two 32-bit event mask words: eventMask.0 for events 0-31 and eventMask.1 for events 32-63. For LE Meta Event (code 0x3E = 62), this meant bit 30 was incorrectly set in eventMask.0 instead of eventMask.1, causing the kernel to filter out all LE Meta events. This made BLE scanning non-functional - the stream would be created successfully but never yield any results. The fix routes events >= 32 to eventMask.1 with the appropriate bit offset. Tested on Linux 6.8 with Realtek USB Bluetooth adapter - scanning now correctly discovers BLE devices.
The lowEnergyClient() method was returning immediately after starting a non-blocking connect, without waiting for the connection to actually complete. For non-blocking sockets, connect() returns EINPROGRESS and the caller must poll for writability to know when the connection is established. This caused GATT operations to fail because the socket wasn't actually connected when the GATT client tried to use it. The fix: 1. Catches EINPROGRESS from the non-blocking connect 2. Polls for writability with a 30 second timeout 3. Checks for error/hangup events indicating connection failure 4. Only returns the socket once the connection is confirmed
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Summary
Fix the
setEvent()method inCInterop.HCIFilterSocketOptionto correctly handle HCI events with codes >= 32.Problem
The current implementation always sets bits in
eventMask.0, even for events >= 32. The HCI filter structure uses two 32-bit event mask words:eventMask.0for events 0-31eventMask.1for events 32-63For LE Meta Event (code 0x3E = 62):
bit = 62 & 63 = 62HCISetBit(62, &eventMask.0)attempts to set bit 62 in a 32-bit integerThis results in the LE Meta events being filtered out by the kernel, making all BLE scanning non-functional.
Symptoms
lowEnergyScan()returns a validAsyncLowEnergyScanStreambtmonshows LE Advertising Reports ARE being received by the kernelVerification
Tested on Linux 6.8.0-90-generic (Ubuntu 24.04) with Realtek USB Bluetooth adapter. After the fix, scanning correctly discovers BLE devices:
Possibly Related
This may be related to #40 - while that issue reports a different error, the underlying cause (improper HCI filter configuration) is similar.