快速将 NSData 转换为 sockaddr 结构 [重复]

Question

我正在尝试快速进行简单的 DNS 查找。到目前为止，这是我拥有的代码：

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

此时，"addresses" NSArray 中的每个元素都是一个包装了 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它时，这会打印出看起来有效的数据。这是我卡住的地方。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 COpaquePointer? 类型的 address.bytes 转换为 c 结构？任何帮助表示赞赏。我正在努力解决这个问题。

Answer 1

对于使用getnameinfo 的更简单的解决方案，请在此处查看 Martin 的回答：How can I get a real IP address from DNS query in Swift?

为 Swift 5 / IPv6 更新：

CFHostGetAddressing 返回的对象可以作为Data 桥接到 Swift，并使用withUnsafeBytes 和assumingMemoryBound(to:) 转换为in_addr/in6_addr。

这是一个使用inet_ntop 将 IPv4/IPv6 地址转换为字符串的完整示例：

import CFNetwork
import Foundation

protocol NetworkAddress {
    static var family: Int32 { get }
    static var maxStringLength: Int32 { get }
}
extension in_addr: NetworkAddress {
    static let family = AF_INET
    static let maxStringLength = INET_ADDRSTRLEN
}
extension in6_addr: NetworkAddress {
    static let family = AF_INET6
    static let maxStringLength = INET6_ADDRSTRLEN
}

extension String {
    init<A: NetworkAddress>(address: A) {
        // allocate a temporary buffer large enough to hold the string
        var buf = ContiguousArray<Int8>(repeating: 0, count: Int(A.maxStringLength))
        self = withUnsafePointer(to: address) { rawAddr in
            buf.withUnsafeMutableBufferPointer {
                String(cString: inet_ntop(A.family, rawAddr, $0.baseAddress, UInt32($0.count)))
            }
        }
    }
}

func addressToString(data: Data) -> String? {
    return data.withUnsafeBytes {
        let family = $0.baseAddress!.assumingMemoryBound(to: sockaddr_storage.self).pointee.ss_family
        // family determines which address type to cast to (IPv4 vs IPv6)
        if family == numericCast(AF_INET) {
            return String(address: $0.baseAddress!.assumingMemoryBound(to: sockaddr_in.self).pointee.sin_addr)
        } else if family == numericCast(AF_INET6) {
            return String(address: $0.baseAddress!.assumingMemoryBound(to: sockaddr_in6.self).pointee.sin6_addr)
        }
        return nil
    }
}

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

print(addresses?.compactMap(addressToString))

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)

为 Swift 3 更新：

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))
    }
}

---

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))
}

更多讨论请见Swift: Pass Uninitialized C Structure to Imported C function