RSE/Backend/Helper/FilterHelper.cs

using System.Text.RegularExpressions;

namespace Backend.Helper;

public static class FilterHelper
{
    // https://stackoverflow.com/a/56116499
    private const string DomainPattern = @"^(?:http(s)?:\/\/)?[\w.-]+(?:\.[\w\.-]+)+[\w\-\._~:/?#[\]@!\$&'\(\)\*\+,;=.]+$";
    
    public static void GetDomain(string data, out string result)
    {
        result = "";
        const string searchTerm = "CN=";
        
        if (!data.Contains("subject:") || !data.Contains(searchTerm)) return;
        
        int start = data.LastIndexOf(searchTerm, StringComparison.Ordinal) + searchTerm.Length;
        int end = data.Length;
        
        result = GetSubstring(data, start, end);
        
        bool isValid = ValidateUrl(result);
        
        if (!isValid)
        {
            result = "";
        }
    }
    
    public static void GetServerType(string data, out string result)
    {
        result = "";
        const string searchTerm = "Server:";
        
        if (!data.Contains(searchTerm)) return;
        
        int start = data.LastIndexOf(searchTerm, StringComparison.Ordinal) + searchTerm.Length;
        int end = data.Length;
        
        result = GetSubstring(data, start, end);
    }
    
    public static void GetHttpVersion(string data, out string result)
    {
        result = "";
        const string searchTerm = "> HEAD / ";
        
        if (!data.Contains(searchTerm)) return;
        
        int start = data.LastIndexOf(searchTerm, StringComparison.Ordinal) + searchTerm.Length;
        int end = data.Length;
        
        result = GetSubstring(data, start, end);
    }
    
    public static void GetALPN(string data, out string result)
    {
        result = "";
        const string searchTerm = "* ALPN: server accepted ";
        
        if (!data.Contains(searchTerm)) return;
        
        int start = data.LastIndexOf(searchTerm, StringComparison.Ordinal) + searchTerm.Length;
        int end = data.Length;
        
        result = GetSubstring(data, start, end);
    }
    
    public static void GetCertificateIssuerCountry(string data, out string result)
    {
        result = "";
        const string searchTerm = "issuer: C=";
        
        if (!data.Contains(searchTerm)) return;
        
        int start = data.LastIndexOf(searchTerm, StringComparison.Ordinal) + searchTerm.Length;
        int end = data.IndexOf(';', StringComparison.Ordinal);
        
        result = GetSubstring(data, start, end);
    }
    
    public static void GetCertificateOrganizationName(string data, out string result)
    {
        result = "";
        const string searchTerm = "O=";
        
        if (!data.Contains(searchTerm)) return;
        
        int start = data.LastIndexOf(searchTerm, StringComparison.Ordinal) + searchTerm.Length;
        int end = data.IndexOf(';', StringComparison.Ordinal);
        
        result = GetSubstring(data, start, end);
    }
    
    public static void GetIpV6(string data, out string result)
    {
        result = "";
        const string searchTerm = "IPv6: ";
        
        if (!data.Contains(searchTerm)) return;
        
        int start = data.LastIndexOf(searchTerm, StringComparison.Ordinal) + searchTerm.Length;
        int end = data.Length;
        
        result = GetSubstring(data, start, end);
    }
    
    public static void GetTlsVersion(string data, out string result)
    {
        result = "";
        const string searchTerm = "SSL connection using ";
        
        if (!data.Contains(searchTerm)) return;
        
        int start = data.LastIndexOf(searchTerm, StringComparison.Ordinal) + searchTerm.Length;
        int end = data.IndexOf('/') - 1;
        
        result = GetSubstring(data, start, end);
    }
    
    public static void GetConnection(string data, out string result)
    {
        result = "";
        const string searchTerm = "< Connection: ";
        
        if (!data.Contains(searchTerm)) return;
        
        int start = data.LastIndexOf(searchTerm, StringComparison.Ordinal) + searchTerm.Length;
        int end = data.Length;
        
        result = GetSubstring(data, start, end);
    }
    
    public static void GetEncoding(string data, out string result)
    {
        result = "";
        const string searchTerm = "< Vary: ";
        
        if (!data.Contains(searchTerm)) return;
        
        int start = data.LastIndexOf(searchTerm, StringComparison.Ordinal) + searchTerm.Length;
        int end = data.Length;
        
        result = GetSubstring(data, start, end);
    }
    
    public static void GetPublicKeyType(string data, out string result, string searchTerm)
    {
        result = "";
        
        if (!data.Contains(searchTerm)) return;
        
        int start = data.LastIndexOf(searchTerm, StringComparison.Ordinal) + searchTerm.Length;
        int end = data.Length;
        
        result = GetSubstring(data, start, end);
    }
    
    public static void GetKeyExchangeAlgorithm(string data, out string result)
    {
        result = "";
        const string searchTerm = "* SSL connection using ";
        
        if (!data.Contains(searchTerm) || string.IsNullOrWhiteSpace(data)) return;
        
        string[] temp = data.Split('/');
        
        switch (temp.Length)
        {
            case 0:
                return;
            case 2:
                result = $"{temp[1].Trim()}";
                return;
            default:
                result = temp[2].Trim();
                break;
        }
    }
    
    public static void GetCipherSuite(string data, out string result)
    {
        result = "";
        const string searchTerm = "* SSL connection using ";
        
        if (!data.Contains(searchTerm)) return;
        
        string[] temp = data.Split('/');
        
        result = temp[1].Trim();
    }
    
    private static string GetSubstring(string input, int start, int end)
    {
        try
        {
            if (start >= end)
            {
                return "";
            }
            
            return input.AsSpan().Slice(start, end - start).ToString();
        }
        catch (Exception e)
        {
            Console.WriteLine($"start index {start} end index {end}");
            Console.WriteLine();
            Console.WriteLine(e);
        }
        
        return "";
    }
    
    private static bool ValidateUrl(string url)
    {
        Regex rgx = new(DomainPattern);
        return rgx.IsMatch(url);
    }
}