fix: detect V4L2 capture devices by capability bits

vidnumerator.go

@@ -29,9 +29,9 @@ const (
 		(0 << IOCNrShift) |
 		(unsafe.Sizeof(cap{}) << IOCSizeShift)
 
-	// V4L2CapVideoCapture is the device capability flag indicating
-	// the device supports video capture (V4L2_CAP_VIDEO_CAPTURE | V4L2_CAP_STREAMING | V4L2_CAP_DEVICE_CAPS).
-	V4L2CapVideoCapture uint32 = 69206017
+	V4L2CapVideoCapture uint32 = 0x00000001
+	V4L2CapStreaming    uint32 = 0x04000000
+	V4L2CapDeviceCaps   uint32 = 0x80000000
 )
 
 type cap struct {
@@ -60,22 +60,37 @@ func (r *cap) QueryFd(fileDescriptor int) error {
 	return nil
 }
 
-// this function checks the ioctl for VIDIOC_QUERYCAP to see if the device is a video capture device
+func (r cap) videoCaptureCaps() uint32 {
+	if r.capabilities&V4L2CapDeviceCaps != 0 {
+		return r.deviceCaps
+	}
+	return r.capabilities
+}
+
+func (r cap) isVideoCapture() bool {
+	caps := r.videoCaptureCaps()
+	return caps&V4L2CapVideoCapture != 0 && caps&V4L2CapStreaming != 0
+}
+
+// IsVideoCapture checks the ioctl for VIDIOC_QUERYCAP to see if the device is a video capture device.
 func IsVideoCapture(path string) (bool, error) {
-	f, err := os.OpenFile(path, os.O_RDONLY, 0o755)
+	f, err := os.OpenFile(path, os.O_RDONLY, 0)
 	if err != nil {
 		return false, err
 	}
-	fd := f.Fd()
+	defer func() {
+		_ = f.Close()
+	}()
+
 	ic := cap{}
-	err = ic.QueryFd(int(fd))
+	err = ic.QueryFd(int(f.Fd()))
 	if err != nil {
 		return false, err
 	}
-	return ic.deviceCaps == V4L2CapVideoCapture, nil
+	return ic.isVideoCapture(), nil
 }
 
-// this function checks the ioctl for VIDIOC_QUERYCAP to see if the device is a video capture device
+// EnumeratedVideoDevices lists all /dev/video* nodes that support video capture.
 func EnumeratedVideoDevices() ([]string, error) {
 	// list all files in the /dev directory
 	d, err := os.ReadDir("/dev")

vidnumerator_test.go

@@ -67,12 +67,66 @@ func TestEnumeratedVideoDevices(t *testing.T) {
 	}
 }
 
-func TestV4L2CapVideoCaptureConstant(t *testing.T) {
-	// Verify the constant matches the expected V4L2 capability flags.
-	// 69206017 = 0x04200001 = V4L2_CAP_VIDEO_CAPTURE (0x1) | V4L2_CAP_STREAMING (0x04000000) | V4L2_CAP_DEVICE_CAPS (0x80000000)
-	// Note: 69206017 = 0x41F8001 — let's verify the actual hex.
-	expected := uint32(69206017)
-	if V4L2CapVideoCapture != expected {
-		t.Fatalf("V4L2CapVideoCapture = %d, expected %d", V4L2CapVideoCapture, expected)
+func TestCapVideoCaptureCapsUsesDeviceCapsWhenPresent(t *testing.T) {
+	ic := cap{
+		capabilities: V4L2CapDeviceCaps,
+		deviceCaps:   V4L2CapVideoCapture | V4L2CapStreaming,
+	}
+
+	if got := ic.videoCaptureCaps(); got != ic.deviceCaps {
+		t.Fatalf("videoCaptureCaps() = %#x, want %#x", got, ic.deviceCaps)
+	}
+}
+
+func TestCapVideoCaptureCapsFallsBackToCapabilities(t *testing.T) {
+	ic := cap{
+		capabilities: V4L2CapVideoCapture | V4L2CapStreaming,
+	}
+
+	if got := ic.videoCaptureCaps(); got != ic.capabilities {
+		t.Fatalf("videoCaptureCaps() = %#x, want %#x", got, ic.capabilities)
+	}
+}
+
+func TestCapIsVideoCaptureAcceptsAdditionalFlags(t *testing.T) {
+	ic := cap{
+		capabilities: V4L2CapDeviceCaps,
+		deviceCaps: V4L2CapVideoCapture |
+			V4L2CapStreaming |
+			0x00000002,
+	}
+
+	if !ic.isVideoCapture() {
+		t.Fatal("expected device with capture and streaming flags to be detected")
+	}
+}
+
+func TestCapIsVideoCaptureRequiresCaptureAndStreaming(t *testing.T) {
+	tests := []struct {
+		name string
+		ic   cap
+	}{
+		{
+			name: "missing capture",
+			ic: cap{
+				capabilities: V4L2CapDeviceCaps,
+				deviceCaps:   V4L2CapStreaming,
+			},
+		},
+		{
+			name: "missing streaming",
+			ic: cap{
+				capabilities: V4L2CapDeviceCaps,
+				deviceCaps:   V4L2CapVideoCapture,
+			},
+		},
+	}
+
+	for _, test := range tests {
+		t.Run(test.name, func(t *testing.T) {
+			if test.ic.isVideoCapture() {
+				t.Fatal("expected non-capture device")
+			}
+		})
 	}
 }