CFHostBlockingLookups.swift

import Foundation

enum HostResult {
    case success([String])
    case failure(String)
    var description: String {
        switch self {
        case let .success(addresses): return "\(addresses)"
        case let .failure(error): return "\(error)"
        }
    }
}

// https://developer.apple.com/library/mac/documentation/CoreFoundation/Reference/CFStreamConstants/index.html#//apple_ref/doc/constant_group/CFStream_Error_Domain_Constants_CFHost_
extension CFStreamError {
    var description: String {
        switch (domain, error) {
        case (CFIndex(kCFStreamErrorDomainNetDB), EAI_NONAME):
            return "NetDB error: hostname nor servname provided, or not known"
        default:
            return "error \(error) domain \(domain)"
        }
    }
}

func stringForIPAddress(address: NSData) -> String? {

    var hostBuf = Array<Int8>(repeating: 0, count: Int(NI_MAXHOST))

    if getnameinfo(
        UnsafePointer<sockaddr>(address.bytes), socklen_t(address.length),
        &hostBuf, socklen_t(hostBuf.count),
        nil, 0,
        NI_NUMERICHOST | NI_NUMERICSERV) != 0 {
        return nil
    }

    return String(cString: hostBuf)
}

func lookupAddresses(name: String) -> HostResult {

    let host = CFHostCreateWithName(kCFAllocatorDefault, name).takeRetainedValue()

    var error = CFStreamError()
    let didStart = CFHostStartInfoResolution(host, .addresses, &error)
    if error.error != 0 {
        return .failure("😡 \(error.description)")
    }

    if !didStart {
        return .failure("❌ Failed to start info resolution")
    }

    var resolved = DarwinBoolean(false)
    guard let dataArray = (CFHostGetAddressing(host, &resolved)?.takeUnretainedValue() as [AnyObject]?) as? [NSData] else {
        return .failure("💣 Error getting addresses")
    }

    return .success(dataArray.flatMap { stringForIPAddress(address: $0) })
}


// ---------------------------------------

lookupAddresses(name: "localhost")              // -> ["::1", "127.0.0.1"]
lookupAddresses(name: "google.com")             // -> ["216.58.220.142"]
lookupAddresses(name: "facebook.com")           // -> ["69.171.230.68"]
lookupAddresses(name: "v6.google.com")          // -> "😡 NetDB error: hostname nor servname provided, or not known"
lookupAddresses(name: "v6.vvv.facebook.com")    // -> "😡 NetDB error: hostname nor servname provided, or not known"