PublicWeb.cs

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using System.Net;
using System.Net.Sockets;

namespace Lilith.Core.WebResearch;

public static class PublicWeb
{
    public static Uri ValidateUri(string value)
    {
        if (!Uri.TryCreate(value, UriKind.Absolute, out var uri) || uri.Scheme is not ("https" or "http") || !string.IsNullOrEmpty(uri.UserInfo) || !uri.IsDefaultPort || uri.HostNameType == UriHostNameType.Unknown) throw new ArgumentException("Only public HTTP(S) pages on standard ports are supported.");
        string host = uri.DnsSafeHost.TrimEnd('.').ToLowerInvariant();
        if (!host.Contains('.') || host.EndsWith(".localhost") || host.EndsWith(".local") || host.EndsWith(".internal") || host.EndsWith(".test") || host.EndsWith(".invalid") || host.EndsWith(".onion") || IPAddress.TryParse(host.Trim('[', ']'), out var ip) && !IsPublic(ip)) throw new ArgumentException("Private and local web destinations are not allowed.");
        return new UriBuilder(uri) { Fragment = "" }.Uri;
    }
    public static bool IsPublic(IPAddress address)
    {
        if (address.IsIPv4MappedToIPv6) address = address.MapToIPv4();
        byte[] b = address.GetAddressBytes();
        if (address.AddressFamily == AddressFamily.InterNetworkV6)
            return (b[0] & 0xe0) == 0x20 && !(b[0] == 0x20 && b[1] == 0x01 && b[2] == 0x0d && b[3] == 0xb8) && !(b[0] == 0x20 && b[1] == 0x02) && !(b[0] == 0x20 && b[1] == 0x01 && b[2] == 0 && b[3] == 0);
        return b[0] is not (0 or 10 or 127) && b[0] < 224 && !(b[0] == 100 && b[1] is >= 64 and <= 127) && !(b[0] == 169 && b[1] == 254) && !(b[0] == 172 && b[1] is >= 16 and <= 31) && !(b[0] == 192 && (b[1] == 168 || b[1] == 0 || b[1] == 2)) && !(b[0] == 198 && (b[1] is 18 or 19 || b[1] == 51 && b[2] == 100)) && !(b[0] == 203 && b[1] == 0 && b[2] == 113);
    }
}