wireguard-apple/WireGuard/Shared/Model/IPAddressRange.swift

// SPDX-License-Identifier: MIT
// Copyright © 2018 WireGuard LLC. All Rights Reserved.

import Foundation
import Network

struct IPAddressRange {
    let address: IPAddress
    var networkPrefixLength: UInt8
    
    init(address: IPAddress, networkPrefixLength: UInt8) {
        self.address = address
        self.networkPrefixLength = networkPrefixLength
    }
}

extension IPAddressRange {
    var stringRepresentation: String {
        return "\(address)/\(networkPrefixLength)"
    }
    
    init?(from string: String) {
        guard let parsed = IPAddressRange.parseAddressString(string) else { return nil }
        address = parsed.0
        networkPrefixLength = parsed.1
    }
    
    private static func parseAddressString(_ string: String) -> (IPAddress, UInt8)? {
        let endOfIPAddress = string.lastIndex(of: "/") ?? string.endIndex
        let addressString = String(string[string.startIndex ..< endOfIPAddress])
        let address: IPAddress
        if let addr = IPv4Address(addressString) {
            address = addr
        } else if let addr = IPv6Address(addressString) {
            address = addr
        } else {
            return nil
        }
        
        let maxNetworkPrefixLength: UInt8 = address is IPv4Address ? 32 : 128
        var networkPrefixLength: UInt8
        if endOfIPAddress < string.endIndex { // "/" was located
            let indexOfNetworkPrefixLength = string.index(after: endOfIPAddress)
            guard indexOfNetworkPrefixLength < string.endIndex else { return nil }
            let networkPrefixLengthSubstring = string[indexOfNetworkPrefixLength ..< string.endIndex]
            guard let npl = UInt8(networkPrefixLengthSubstring) else { return nil }
            networkPrefixLength = min(npl, maxNetworkPrefixLength)
        } else {
            networkPrefixLength = maxNetworkPrefixLength
        }
        
        return (address, networkPrefixLength)
    }
}