47 lines
1.9 KiB
Swift
47 lines
1.9 KiB
Swift
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import Foundation
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import Darwin
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/// Best-effort reverse DNS (IP -> PTR hostname). Blocking — call it off the main
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/// thread. Returns nil when there's no PTR record (we don't want a numeric echo).
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public enum ReverseDNS {
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public static func resolve(_ ip: String) -> String? {
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var storage = sockaddr_storage()
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var length: socklen_t = 0
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if ip.contains(":") {
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var sa = sockaddr_in6()
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sa.sin6_family = sa_family_t(AF_INET6)
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sa.sin6_len = UInt8(MemoryLayout<sockaddr_in6>.size)
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guard inet_pton(AF_INET6, ip, &sa.sin6_addr) == 1 else { return nil }
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withUnsafeBytes(of: &sa) { src in
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withUnsafeMutableBytes(of: &storage) { dst in
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dst.copyMemory(from: UnsafeRawBufferPointer(rebasing: src[0..<MemoryLayout<sockaddr_in6>.size]))
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}
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}
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length = socklen_t(MemoryLayout<sockaddr_in6>.size)
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} else {
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var sa = sockaddr_in()
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sa.sin_family = sa_family_t(AF_INET)
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sa.sin_len = UInt8(MemoryLayout<sockaddr_in>.size)
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guard inet_pton(AF_INET, ip, &sa.sin_addr) == 1 else { return nil }
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withUnsafeBytes(of: &sa) { src in
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withUnsafeMutableBytes(of: &storage) { dst in
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dst.copyMemory(from: UnsafeRawBufferPointer(rebasing: src[0..<MemoryLayout<sockaddr_in>.size]))
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}
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}
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length = socklen_t(MemoryLayout<sockaddr_in>.size)
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}
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var host = [CChar](repeating: 0, count: Int(NI_MAXHOST))
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let result = withUnsafePointer(to: &storage) { ptr in
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ptr.withMemoryRebound(to: sockaddr.self, capacity: 1) { sa in
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getnameinfo(sa, length, &host, socklen_t(host.count), nil, 0, NI_NAMEREQD)
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}
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}
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guard result == 0 else { return nil }
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let name = String(cString: host)
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return name.isEmpty ? nil : name
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}
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}
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