DnsUpdater/Sources/App/Model/IPAddressCheck.swift

import Foundation

struct IPAddressCheck {

    private var ipv4Request: URLRequest {
        let url = URL(string: "http://fritz.box:49000/igdupnp/control/WANIPConn1")!
        var request = URLRequest(url: url)
        request.setValue("text/xml; charset=utf-8",
                         forHTTPHeaderField: "Content-Type")
        request.setValue("urn:schemas-upnp-org:service:WANIPConnection:1#GetExternalIPAddress",
                         forHTTPHeaderField: "SOAPAction")
        let body = """
    <?xml version="1.0" encoding="utf-8"?>
    <s:Envelope xmlns:s="http://schemas.xmlsoap.org/soap/envelope/" s:encodingStyle="http://schemas.xmlsoap.org/soap/encoding/">
        <s:Body>
            <u:GetExternalIPAddress xmlns:u="urn:schemas-upnp-org:service:WANIPConnection:1" />
        </s:Body>
    </s:Envelope>
    """
        request.httpMethod = "POST"
        request.httpBody = body.data(using: .utf8)!
        return request
    }

    func determineIPv4() async throws -> String {
        let data: Data
        let response: URLResponse
        do {
            (data, response) = try await URLSession.shared.data(for: ipv4Request)
        } catch {
            throw DNSError.routerRequestFailedForIPv4(error)
        }
        
        guard let httpResponse = response as? HTTPURLResponse else {
            throw DNSError.invalidRouterResponseForIPv4
        }
        guard httpResponse.statusCode == 200 else {
            throw DNSError.invalidRouterResponseCodeForIPv4(httpResponse.statusCode)
        }
        guard let responseBody = String(data: data, encoding: .utf8) else {
            throw DNSError.invalidRouterResponseBodyForIPv4
        }

        let ipString = responseBody
            .components(separatedBy: "<NewExternalIPAddress>").last!
            .components(separatedBy: "</NewExternalIPAddress>").first!
        let parts = ipString.components(separatedBy: ".")
        guard parts.count == 4 else {
            throw DNSError.invalidRouterResponseIpForIPv4(ipString)
        }
        let numbers = parts.compactMap(Int.init)
        guard numbers.count == 4 else {
            throw DNSError.invalidRouterResponseIpForIPv4(ipString)
        }
        guard numbers.contains(where: { $0 != 0 }) else {
            throw DNSError.invalidRouterResponseIpForIPv4(ipString)
        }
        return ipString
    }

    private func execute(_ command: String) throws -> (code: Int, output: String) {
        let task = Process()
        let pipe = Pipe()

        task.standardOutput = pipe
        task.standardError = pipe
        task.arguments = ["-cl", command]
        task.executableURL = URL(fileURLWithPath: "/bin/bash")
        task.standardInput = nil

        try task.run()
        task.waitUntilExit()

        let code = task.terminationStatus

        let data = pipe.fileHandleForReading.readDataToEndOfFile()
        let output = String(data: data, encoding: .utf8)!

        return (Int(code), output)
    }

    func determineIPv6() throws -> String {
#if os(Linux)
        let ipv6Command = "ip addr show"
#elseif os(macOS)
        let ipv6Command = "ifconfig"
#else
        fatalError("Unsupported OS")
#endif

        let code: Int
        let output: String
        do {
            (code, output) = try execute(ipv6Command)
        } catch {
            throw DNSError.failedToPerformCommandForIPv6(error)
        }
        guard code == 0 else {
            throw DNSError.invalidCommandResultForIPv6(code, output)
        }
        let addresses: [String] = output
            .components(separatedBy: "inet6 ")
            .dropFirst()
            .compactMap { $0
                .components(separatedBy: "/").first?
                .components(separatedBy: " ").first
            }
            .compactMap {
                let parts = $0.components(separatedBy: ":")
                guard parts.count == 8 else {
                    return nil
                }
                return $0
            }
        guard let ip = addresses.first else {
            throw DNSError.invalidIpAddressForIPv6(output)
        }
        return ip
    }
}