在swift中将NSData转换为sockaddr结构

Question

我试图在swift中进行简单的DNS查找。到目前为止，这是我的代码：

let hostRef = CFHostCreateWithName(kCFAllocatorDefault, "google.com").takeRetainedValue()
var resolved = CFHostStartInfoResolution(hostRef, CFHostInfoType.Addresses, nil)
let addresses = CFHostGetAddressing(hostRef, &resolved).takeRetainedValue() as NSArray

此时，＆＃34;中的每个元素都解决了＃34; NSArray是一个包装sockaddr结构的CFDataRef对象。

由于CFDataRef可以免费桥接到NSData，我可以像这样循环遍历它们：

for address: AnyObject in addresses {
  println(address)  // address is of type NSData.
}

到目前为止一切顺利（我认为）。当我在单元测试中运行时，这会打印出有效的数据。这是我陷入困境的地方。对于我的生活，我无法弄清楚如何将NSData对象中的字节转换为sockaddr结构。

如何将address.bytes（COpaquePointer？类型）转换为c结构？任何帮助赞赏。我试图弄明白这一点，把头撞在墙上。

Answer 1

您可以使用NSData方法getBytes(_, length:)方法，并使用前缀&运算符将sockaddr结构传递给inout参数：

var data: NSData ...
var address: sockaddr ...

data.getBytes(&address, length: MemoryLayout<sockaddr>.size)

更新了Swift 3：

let host = CFHostCreateWithName(kCFAllocatorDefault, "google.com" as CFString).takeRetainedValue()
var resolved = DarwinBoolean(CFHostStartInfoResolution(host, .addresses, nil))
let addresses = CFHostGetAddressing(host, &resolved)?.takeUnretainedValue() as! [NSData]?

if let data = addresses?.first {
    var storage = sockaddr_storage()
    data.getBytes(&storage, length: MemoryLayout<sockaddr_storage>.size)

    if Int32(storage.ss_family) == AF_INET {
        let addr4 = withUnsafePointer(to: &storage) {
            $0.withMemoryRebound(to: sockaddr_in.self, capacity: 1) {
                $0.pointee
            }
        }

        // prints 74.125.239.132
        print(String(cString: inet_ntoa(addr4.sin_addr), encoding: .ascii))
    }
}

---

2015年6月3日更新： 现在C结构可以很容易地进行零初始化，这变得更加简单：

let host = CFHostCreateWithName(kCFAllocatorDefault, "google.com").takeRetainedValue()
var resolved = CFHostStartInfoResolution(host, .Addresses, nil)
let addresses = CFHostGetAddressing(host, &resolved)?.takeUnretainedValue() as! [NSData]?

if let data = addresses?.first {
    var storage = sockaddr_storage()
    data.getBytes(&storage, length: sizeof(sockaddr_storage))

    if Int32(storage.ss_family) == AF_INET {
        let addr4 = withUnsafePointer(&storage) { UnsafePointer<sockaddr_in>($0).memory }

        // prints 74.125.239.132
        println(String(CString: inet_ntoa(addr4.sin_addr), encoding: NSASCIIStringEncoding))
    }
}

<击>

---

不幸的是，这需要首先初始化sockaddr。为避免这种情况，您可以执行以下操作：

func makeWithUnsafePointer<T>(body: UnsafePointer<T> -> ()) -> T {
    let ptr = UnsafePointer<T>.alloc(sizeof(T))
    body(ptr)
    return ptr.move()
}

let addr: sockaddr = makeWithUnsafePointer {
    data.getBytes($0 as UnsafePointer<sockaddr>, length: sizeof(sockaddr))
}

或者这个：

func makeWithUninitialized<T>(body: inout T -> ()) -> T {
    let ptr = UnsafePointer<T>.alloc(sizeof(T))
    body(&ptr.memory)
    return ptr.move()
}

let addr = makeWithUninitialized { (inout addr: sockaddr) in
    data.getBytes(&addr, length: sizeof(sockaddr))
}

有关更多讨论，请参阅Swift: Pass Uninitialized C Structure to Imported C function