How to implement IOServiceMatchingCallBack in Swift

Question

I would like to detect a specific USB is plugged in/removed in my application. For now, I can get the deviceName with this tutorial Working With USB Device Interfaces. But,

Answer 1

It works after I put the callback function out the class. However, I don't know why.

class IODetection {
    class func monitorUSBEvent(VendorID: Int, ProductID: Int) {


        var portIterator: io_iterator_t = 0
        var kr: kern_return_t = KERN_FAILURE
        let matchingDict = IOServiceMatching(kIOUSBDeviceClassName)

        // Add the VENDOR and PRODUCT IDs to the matching dictionary.
        let vendorIDString = kUSBVendorID as CFStringRef!
        let productIDString = kUSBProductID as CFStringRef!
        CFDictionarySetValue(matchingDict, unsafeAddressOf(vendorIDString), unsafeAddressOf(VendorID))
        CFDictionarySetValue(matchingDict, unsafeAddressOf(productIDString), unsafeAddressOf(ProductID))

        // To set up asynchronous notifications, create a notification port and add its run loop event source to the program’s run loop
        let gNotifyPort: IONotificationPortRef = IONotificationPortCreate(kIOMasterPortDefault)
        let runLoopSource: Unmanaged<CFRunLoopSource>! = IONotificationPortGetRunLoopSource(gNotifyPort)
        let gRunLoop: CFRunLoop! = CFRunLoopGetCurrent()

        CFRunLoopAddSource(gRunLoop, runLoopSource.takeRetainedValue(), kCFRunLoopDefaultMode)

        // MARK: - USB in Notification
        let observer = UnsafeMutablePointer<Void>(unsafeAddressOf(self))
        kr = IOServiceAddMatchingNotification(gNotifyPort,
                                              kIOMatchedNotification,
                                              matchingDict,
                                              deviceAdded,
                                              observer,
                                              &portIterator)
        deviceAdded(nil, iterator: portIterator)


        // MARK: - USB remove Notification
        kr = IOServiceAddMatchingNotification(gNotifyPort,
                                              kIOTerminatedNotification,
                                              matchingDict,
                                              deviceRemoved,
                                              observer,
                                              &portIterator)
        deviceRemoved(nil, iterator: portIterator)

    }
}

func deviceAdded(refCon: UnsafeMutablePointer<Void>, iterator: io_iterator_t) -> Void {
    var kr: kern_return_t = KERN_FAILURE

    while case let usbDevice = IOIteratorNext(iterator) where usbDevice != 0 {
        let deviceNameAsCFString = UnsafeMutablePointer<io_name_t>.alloc(1)
        defer {deviceNameAsCFString.dealloc(1)}
        kr = IORegistryEntryGetName(usbDevice, UnsafeMutablePointer(deviceNameAsCFString))
        if kr != KERN_SUCCESS {
            deviceNameAsCFString.memory.0 = 0
        }
        let deviceName = String.fromCString(UnsafePointer(deviceNameAsCFString))
        print("Device Added: \(deviceName!)")

        // Do something if I get the specific device
        if deviceName == "YOUR DEVICE" {
            /// Your Action HERE
        }

        IOObjectRelease(usbDevice)
    }
}

Answer 2

Here's a Swift 3 version, using closures instead of global functions (a closure w/o a context can be bridged to a C function pointer), using GCD instead of Runloops (much nicer API), using callbacks and dispatches to inform about events and using real objects instead of static objects or singletons:

import Darwin
import IOKit
import IOKit.usb
import Foundation


class IOUSBDetector {

    enum Event {
        case Matched
        case Terminated
    }

    let vendorID: Int
    let productID: Int

    var callbackQueue: DispatchQueue?

    var callback: (
        ( _ detector: IOUSBDetector,  _ event: Event,
            _ service: io_service_t
        ) -> Void
    )?


    private
    let internalQueue: DispatchQueue

    private
    let notifyPort: IONotificationPortRef

    private
    var matchedIterator: io_iterator_t = 0

    private
    var terminatedIterator: io_iterator_t = 0


    private
    func dispatchEvent (
        event: Event, iterator: io_iterator_t
    ) {
        repeat {
            let nextService = IOIteratorNext(iterator)
            guard nextService != 0 else { break }
            if let cb = self.callback, let q = self.callbackQueue {
                q.async {
                    cb(self, event, nextService)
                    IOObjectRelease(nextService)
                }
            } else {
                IOObjectRelease(nextService)
            }
        } while (true)
    }


    init? ( vendorID: Int, productID: Int ) {
        self.vendorID = vendorID
        self.productID = productID
        self.internalQueue = DispatchQueue(label: "IODetector")

        guard let notifyPort = IONotificationPortCreate(kIOMasterPortDefault) else {
            return nil
        }

        self.notifyPort = notifyPort
        IONotificationPortSetDispatchQueue(notifyPort, self.internalQueue)
    }

    deinit {
        self.stopDetection()
    }


    func startDetection ( ) -> Bool {
        guard matchedIterator == 0 else { return true }

        let matchingDict = IOServiceMatching(kIOUSBDeviceClassName)
            as NSMutableDictionary
        matchingDict[kUSBVendorID] = NSNumber(value: vendorID)
        matchingDict[kUSBProductID] = NSNumber(value: productID)

        let matchCallback: IOServiceMatchingCallback = {
            (userData, iterator) in
                let detector = Unmanaged<IOUSBDetector>
                    .fromOpaque(userData!).takeUnretainedValue()
                detector.dispatchEvent(
                    event: .Matched, iterator: iterator
                )
        };
        let termCallback: IOServiceMatchingCallback = {
            (userData, iterator) in
                let detector = Unmanaged<IOUSBDetector>
                    .fromOpaque(userData!).takeUnretainedValue()
                detector.dispatchEvent(
                    event: .Terminated, iterator: iterator
                )
        };

        let selfPtr = Unmanaged.passUnretained(self).toOpaque()

        let addMatchError = IOServiceAddMatchingNotification(
            self.notifyPort, kIOFirstMatchNotification,
            matchingDict, matchCallback, selfPtr, &self.matchedIterator
        )
        let addTermError = IOServiceAddMatchingNotification(
            self.notifyPort, kIOTerminatedNotification,
            matchingDict, termCallback, selfPtr, &self.terminatedIterator
        )

        guard addMatchError == 0 && addTermError == 0 else {
            if self.matchedIterator != 0 {
                IOObjectRelease(self.matchedIterator)
                self.matchedIterator = 0
            }
            if self.terminatedIterator != 0 {
                IOObjectRelease(self.terminatedIterator)
                self.terminatedIterator = 0
            }
            return false
        }

        // This is required even if nothing was found to "arm" the callback
        self.dispatchEvent(event: .Matched, iterator: self.matchedIterator)
        self.dispatchEvent(event: .Terminated, iterator: self.terminatedIterator)

        return true
    }


    func stopDetection ( ) {
        guard self.matchedIterator != 0 else { return }
        IOObjectRelease(self.matchedIterator)
        IOObjectRelease(self.terminatedIterator)
        self.matchedIterator = 0
        self.terminatedIterator = 0
    }
}

And here is some simple test code to test that class (set product and vendor ID as appropriate for your USB device):

let test = IOUSBDetector(vendorID: 0x4e8, productID: 0x1a23)
test?.callbackQueue = DispatchQueue.global()
test?.callback = {
    (detector, event, service) in
        print("Event \(event)")
};
_ = test?.startDetection()
while true { sleep(1) }

Answer 3

Got this working thanks! Only problem was that I wasn't using the iterator in my callback function, so that function wasn't even getting called! Seems like strange behaviour to me, but that was my problem