Disambiguate cameras with same product/vendor ids (issue #59)

Fix issue where `AVCaptureDevice.usbDevice()` would return a USBDevice
pointing to the wrong camera if multiple cameras with the same product
id and vendor id are attached to the computer.

The new approach is to use an iterator to lookup the cameras with the
given vendor and product ids, and then loop through the results and
match against their property dictionaries against the
avDevice.localizedName since that seems to be the only reliable way to
disambiguate between different cameras with otherwise similar
properties.

Author: jazzychad

CameraController/UVC/Extensions/AVCaptureDevice+USB.swift

@@ -30,17 +30,61 @@ typealias DeviceInterfacePointer = UnsafeMutablePointer<UnsafeMutablePointer<IOU
 
 extension AVCaptureDevice {
     func usbDevice() throws -> USBDevice {
+        var camera: io_service_t = 0
         let cameraInformation = try self.modelID.extractCameraInformation()
         let dictionary: NSMutableDictionary = IOServiceMatching("IOUSBDevice") as NSMutableDictionary
         dictionary["idVendor"] = cameraInformation.vendorId
         dictionary["idProduct"] = cameraInformation.productId
 
-        var interfaceRef: UnsafeMutablePointer<UnsafeMutablePointer<IOUSBInterfaceInterface190>>?
-        let camera: io_service_t = IOServiceGetMatchingService(kIOMasterPortDefault, dictionary)
+        // adding other keys to this dictionary like kUSBProductString, kUSBVendorString, etc don't
+        // seem to have any affect on using IOServiceGetMatchingService to get the correct camera,
+        // so we instead get an iterator for the matching services based on idVendor and idProduct
+        // and fetch their property dicts and then match against the more specific values
+
+        var iter: io_iterator_t = 0
+        if IOServiceGetMatchingServices(kIOMasterPortDefault, dictionary, &iter) == kIOReturnSuccess {
+            var cameraCandidate: io_service_t
+            cameraCandidate = IOIteratorNext(iter)
+            while (cameraCandidate != 0) {
+                var propsRef: Unmanaged<CFMutableDictionary>? = nil
+
+                if IORegistryEntryCreateCFProperties(cameraCandidate, &propsRef, kCFAllocatorDefault, 0) == kIOReturnSuccess {
+                    if let properties = propsRef?.takeRetainedValue() {
+
+                        // these are common keys that might have the device name stored in the propery dictionary
+                        let keysToTry: [String] = ["kUSBProductString", "kUSBVendorString", "USB Product Name", "USB Vendor Name"]
+
+                        var found: Bool = false
+                        for key in keysToTry {
+                            if let cameraName = (properties as NSDictionary)[key] as? String {
+                                if cameraName == self.localizedName {
+                                    // we have a match, use this as the camera
+                                    camera = cameraCandidate
+                                    found = true
+                                    // break out of `for key in keysToTry`
+                                    break
+                                }
+                            }
+                        }
+                        if found {
+                            // break out of `while (cameraCandidate != 0)`
+                            break
+                        }
+                    }
+                }
+                cameraCandidate = IOIteratorNext(iter)
+            }
+        }
+
+        // if we haven't found a camera after looping through the iterator, fallback on GetMatchingService method
+        if camera == 0 {
+            camera = IOServiceGetMatchingService(kIOMasterPortDefault, dictionary)
+        }
         defer {
             let code: kern_return_t = IOObjectRelease(camera)
             assert( code == kIOReturnSuccess )
         }
+        var interfaceRef: UnsafeMutablePointer<UnsafeMutablePointer<IOUSBInterfaceInterface190>>?
         var configDesc: IOUSBConfigurationDescriptorPtr?
         try camera.ioCreatePluginInterfaceFor(service: kIOUSBDeviceUserClientTypeID) {
             let deviceInterface: DeviceInterfacePointer = try $0.getInterface(uuid: kIOUSBDeviceInterfaceID)