# HID Crash Fix for Linphone

## Problem

Linphone crashes on startup with SIGSEGV in `LinphonePrivate::HidDevice::stopPollTimer()` when the user has no read access to `/dev/hidraw*` devices.

## Root Cause

The liblinphone SDK's HID subsystem (for USB headset button support) does not handle permission errors gracefully. When `hid_enumerate()` fails or returns devices that cannot be opened, the subsequent timer handling crashes.

## Solution

Replace `libhidapi-hidraw.so.0.15.0` inside the AppImage with a stub implementation that:
- Returns empty device lists from `hid_enumerate()`
- Returns NULL from all `hid_open*()` functions
- Returns safe error values from all other operations

This disables USB headset button support but prevents the crash.

## Build

```bash
gcc -shared -fPIC -O2 -Wall -Wextra -Wpedantic -std=c11 \
    -o libhidapi-hidraw.so.0.15.0 hidapi_dummy.c
```

## Integration into AppImage

```bash
# Extract
./Linphone-*.AppImage --appimage-extract

# Replace library
cp libhidapi-hidraw.so.0.15.0 squashfs-root/lib/

# Repackage
ARCH=x86_64 appimagetool squashfs-root Linphone-Fixed.AppImage
```

## Alternative: System-wide Fix

Instead of patching the AppImage, grant HID access to users:

```bash
echo 'KERNEL=="hidraw*", TAG+="uaccess", MODE="0666"' | \
    sudo tee /etc/udev/rules.d/99-hidraw-permissions.rules
sudo udevadm control --reload-rules && sudo udevadm trigger
```

## Files

- `hidapi_dummy.c` - Complete HIDAPI 0.15.0 stub implementation (25 functions)