System.Net.Dns.InternalGetHostByName C# (CSharp) Метод

        private static IPHostEntry InternalGetHostByName(string hostName, bool includeIPv6)
        {
            if (NetEventSource.IsEnabled) NetEventSource.Enter(null, hostName);
            IPHostEntry ipHostEntry = null;

            if (hostName.Length > MaxHostName // If 255 chars, the last one must be a dot.
                || hostName.Length == MaxHostName && hostName[MaxHostName - 1] != '.')
            {
                throw new ArgumentOutOfRangeException(nameof(hostName), SR.Format(SR.net_toolong,
                    nameof(hostName), MaxHostName.ToString(NumberFormatInfo.CurrentInfo)));
            }

            //
            // IPv6 Changes: IPv6 requires the use of getaddrinfo() rather
            //               than the traditional IPv4 gethostbyaddr() / gethostbyname().
            //               getaddrinfo() is also protocol independent in that it will also
            //               resolve IPv4 names / addresses. As a result, it is the preferred
            //               resolution mechanism on platforms that support it (Windows 5.1+).
            //               If getaddrinfo() is unsupported, IPv6 resolution does not work.
            //
            // Consider    : If IPv6 is disabled, we could detect IPv6 addresses
            //               and throw an unsupported platform exception.
            //
            // Note        : Whilst getaddrinfo is available on WinXP+, we only
            //               use it if IPv6 is enabled (platform is part of that
            //               decision). This is done to minimize the number of
            //               possible tests that are needed.
            //
            if (includeIPv6 || SocketProtocolSupportPal.OSSupportsIPv6)
            {
                //
                // IPv6 enabled: use getaddrinfo() to obtain DNS information.
                //
                int nativeErrorCode;
                SocketError errorCode = NameResolutionPal.TryGetAddrInfo(hostName, out ipHostEntry, out nativeErrorCode);
                if (errorCode != SocketError.Success)
                {
                    throw SocketExceptionFactory.CreateSocketException(errorCode, nativeErrorCode);
                }
            }
            else
            {
                ipHostEntry = NameResolutionPal.GetHostByName(hostName);
            }

            if (NetEventSource.IsEnabled) NetEventSource.Exit(null, ipHostEntry);
            return ipHostEntry;
        } // GetHostByName

        public string dnsResolve(string host)
        {
            GlobalLog.Print("WebProxyScriptHelper::dnsResolve() host:" + ValidationHelper.ToString(host));
            if (host == null)
            {
                if (Logging.On)
                {
                    Logging.PrintWarning(Logging.Web, SR.GetString(SR.net_log_proxy_called_with_null_parameter, "WebProxyScriptHelper.dnsResolve()", "host"));
                }
                throw new ArgumentNullException("host");
            }
            IPHostEntry ipHostEntry = null;

            try
            {
                ipHostEntry = Dns.InternalGetHostByName(host);
            }
            catch { }
            if (ipHostEntry == null)
            {
                return(string.Empty);
            }
            for (int i = 0; i < ipHostEntry.AddressList.Length; i++)
            {
                if (ipHostEntry.AddressList[i].AddressFamily == AddressFamily.InterNetwork)
                {
                    return(ipHostEntry.AddressList[i].ToString());
                }
            }
            return(string.Empty);
        }