How to get MAC address from OS X with Swift

Update to Martin R's entry. There are a couple of lines that won't compile with Swift 2.1.

Change:

let matchingDict = matchingDictUM.takeUnretainedValue() as NSMutableDictionary

To:

let matchingDict = matchingDictUM as NSMutableDictionary

Change:

let macAddressAsString = ":".join(macAddress.map( { String(format:"%02x", $0) } ))

To:

let macAddressAsString = macAddress.map( { String(format:"%02x", $0) } ).joinWithSeparator(":")

Apple's sample code from https://developer.apple.com/library/mac/samplecode/GetPrimaryMACAddress/Introduction/Intro.html to retrieve the Ethernet MAC address can be translated to Swift. I have preserved only the most important comments, more explanations can be found in the original code.

// Returns an iterator containing the primary (built-in) Ethernet interface. The caller is responsible for
// releasing the iterator after the caller is done with it.
func FindEthernetInterfaces() -> io_iterator_t? {

    let matchingDictUM = IOServiceMatching("IOEthernetInterface");
    // Note that another option here would be:
    // matchingDict = IOBSDMatching("en0");
    // but en0: isn't necessarily the primary interface, especially on systems with multiple Ethernet ports.

    if matchingDictUM == nil {
        return nil
    }
    let matchingDict = matchingDictUM.takeUnretainedValue() as NSMutableDictionary
    matchingDict["IOPropertyMatch"] = [ "IOPrimaryInterface" : true]

    var matchingServices : io_iterator_t = 0
    if IOServiceGetMatchingServices(kIOMasterPortDefault, matchingDict, &matchingServices) != KERN_SUCCESS {
        return nil
    }

    return matchingServices
}

// Given an iterator across a set of Ethernet interfaces, return the MAC address of the last one.
// If no interfaces are found the MAC address is set to an empty string.
// In this sample the iterator should contain just the primary interface.
func GetMACAddress(intfIterator : io_iterator_t) -> [UInt8]? {

    var macAddress : [UInt8]?

    var intfService = IOIteratorNext(intfIterator)
    while intfService != 0 {

        var controllerService : io_object_t = 0
        if IORegistryEntryGetParentEntry(intfService, "IOService", &controllerService) == KERN_SUCCESS {

            let dataUM = IORegistryEntryCreateCFProperty(controllerService, "IOMACAddress", kCFAllocatorDefault, 0)
            if dataUM != nil {
                let data = dataUM.takeRetainedValue() as! NSData
                macAddress = [0, 0, 0, 0, 0, 0]
                data.getBytes(&macAddress!, length: macAddress!.count)
            }
            IOObjectRelease(controllerService)
        }

        IOObjectRelease(intfService)
        intfService = IOIteratorNext(intfIterator)
    }

    return macAddress
}


if let intfIterator = FindEthernetInterfaces() {
    if let macAddress = GetMACAddress(intfIterator) {
        let macAddressAsString = ":".join(macAddress.map( { String(format:"%02x", $0) } ))
        println(macAddressAsString)
    }

    IOObjectRelease(intfIterator)
}

The only "tricky" part is how to work with Unmanaged objects, those have the suffix UM in my code.

Instead of returning an error code, the functions return an optional value which is nil if the function failed.

---

Update for Swift 3:

func FindEthernetInterfaces() -> io_iterator_t? {

    let matchingDict = IOServiceMatching("IOEthernetInterface") as NSMutableDictionary
    matchingDict["IOPropertyMatch"] = [ "IOPrimaryInterface" : true]

    var matchingServices : io_iterator_t = 0
    if IOServiceGetMatchingServices(kIOMasterPortDefault, matchingDict, &matchingServices) != KERN_SUCCESS {
        return nil
    }

    return matchingServices
}

func GetMACAddress(_ intfIterator : io_iterator_t) -> [UInt8]? {

    var macAddress : [UInt8]?

    var intfService = IOIteratorNext(intfIterator)
    while intfService != 0 {

        var controllerService : io_object_t = 0
        if IORegistryEntryGetParentEntry(intfService, "IOService", &controllerService) == KERN_SUCCESS {

            let dataUM = IORegistryEntryCreateCFProperty(controllerService, "IOMACAddress" as CFString, kCFAllocatorDefault, 0)
            if let data = dataUM?.takeRetainedValue() as? NSData {
                macAddress = [0, 0, 0, 0, 0, 0]
                data.getBytes(&macAddress!, length: macAddress!.count)
            }
            IOObjectRelease(controllerService)
        }

        IOObjectRelease(intfService)
        intfService = IOIteratorNext(intfIterator)
    }

    return macAddress
}

if let intfIterator = FindEthernetInterfaces() {
    if let macAddress = GetMACAddress(intfIterator) {
        let macAddressAsString = macAddress.map( { String(format:"%02x", $0) } )
            .joined(separator: ":")
        print(macAddressAsString)
    }

    IOObjectRelease(intfIterator)
}

Different approach via if_msghdr

func MACAddressForBSD(bsd : String) -> String?
{
    let MAC_ADDRESS_LENGTH = 6
    let separator = ":"

    var length : size_t = 0
    var buffer : [CChar]

    let bsdIndex = Int32(if_nametoindex(bsd))
    if bsdIndex == 0 {
        print("Error: could not find index for bsd name \(bsd)")
        return nil
    }
    let bsdData = Data(bsd.utf8)
    var managementInfoBase = [CTL_NET, AF_ROUTE, 0, AF_LINK, NET_RT_IFLIST, bsdIndex]

    if sysctl(&managementInfoBase, 6, nil, &length, nil, 0) < 0 {
        print("Error: could not determine length of info data structure");
        return nil;
    }

    buffer = [CChar](unsafeUninitializedCapacity: length, initializingWith: {buffer, initializedCount in
        for x in 0..<length { buffer[x] = 0 }
        initializedCount = length
    })

    if sysctl(&managementInfoBase, 6, &buffer, &length, nil, 0) < 0 {
        print("Error: could not read info data structure");
        return nil;
    }

    let infoData = Data(bytes: buffer, count: length)
    let indexAfterMsghdr = MemoryLayout<if_msghdr>.stride + 1
    let rangeOfToken = infoData[indexAfterMsghdr...].range(of: bsdData)!
    let lower = rangeOfToken.upperBound
    let upper = lower + MAC_ADDRESS_LENGTH
    let macAddressData = infoData[lower..<upper]
    let addressBytes = macAddressData.map{ String(format:"%02x", $0) }
    return addressBytes.joined(separator: separator)
}

MACAddressForBSD(bsd: "en0")

Update for Swift 4.2

func FindEthernetInterfaces() -> io_iterator_t? {

    let matchingDictUM = IOServiceMatching("IOEthernetInterface");
    // Note that another option here would be:
    // matchingDict = IOBSDMatching("en0");
    // but en0: isn't necessarily the primary interface, especially on systems with multiple Ethernet ports.

    if matchingDictUM == nil {
        return nil
    }

    let matchingDict = matchingDictUM! as NSMutableDictionary
    matchingDict["IOPropertyMatch"] = [ "IOPrimaryInterface" : true]

    var matchingServices : io_iterator_t = 0
    if IOServiceGetMatchingServices(kIOMasterPortDefault, matchingDict, &matchingServices) != KERN_SUCCESS {
        return nil
    }

    return matchingServices
}

// Given an iterator across a set of Ethernet interfaces, return the MAC address of the last one.
// If no interfaces are found the MAC address is set to an empty string.
// In this sample the iterator should contain just the primary interface.
func GetMACAddress(_ intfIterator : io_iterator_t) -> [UInt8]? {

    var macAddress : [UInt8]?

    var intfService = IOIteratorNext(intfIterator)
    while intfService != 0 {

        var controllerService : io_object_t = 0
        if IORegistryEntryGetParentEntry(intfService, kIOServicePlane, &controllerService) == KERN_SUCCESS {

            let dataUM = IORegistryEntryCreateCFProperty(controllerService, "IOMACAddress" as CFString, kCFAllocatorDefault, 0)
            if dataUM != nil {
                let data = (dataUM!.takeRetainedValue() as! CFData) as Data
                macAddress = [0, 0, 0, 0, 0, 0]
                data.copyBytes(to: &macAddress!, count: macAddress!.count)
            }
            IOObjectRelease(controllerService)
        }

        IOObjectRelease(intfService)
        intfService = IOIteratorNext(intfIterator)
    }

    return macAddress
}


func getMacAddress() -> String? {
    var macAddressAsString : String?
    if let intfIterator = FindEthernetInterfaces() {
        if let macAddress = GetMACAddress(intfIterator) {
            macAddressAsString = macAddress.map( { String(format:"%02x", $0) } ).joined(separator: ":")
            print(macAddressAsString!)
        }

        IOObjectRelease(intfIterator)
    }
    return macAddressAsString
}