获取指定网页的源码，自动识别编码

/// <summary>
/// 获取指定网页的源码，自动识别编码
/// </summary>
/// <param name="url">网址</param>
/// <returns>源码</returns>
public static string getDataFromUrl(string url)
{
    string str = string.Empty;
    HttpWebRequest request = (HttpWebRequest)HttpWebRequest.Create(url);

    //设置http头
    request.AllowAutoRedirect = true;
    request.AllowWriteStreamBuffering = true;
    request.Referer = "";
    request.Timeout = 10 * 1000;
    request.UserAgent = "";

    HttpWebResponse response = null;
    try
    {
        response = (HttpWebResponse)request.GetResponse();
        if (response.StatusCode == HttpStatusCode.OK)
        {
            //根据http应答的http头来判断编码
            string characterSet = response.CharacterSet;
            Encoding encode;
            if (characterSet != "")
            {
                if (characterSet == "ISO-8859-1")
                {
                    characterSet = "gb2312";
                }
                encode = Encoding.GetEncoding(characterSet);
            }
            else
            {
                encode = Encoding.Default;
            }

            //声明一个内存流来保存http应答流
            Stream receiveStream = response.GetResponseStream();
            MemoryStream mStream = new MemoryStream();

            byte[] bf = new byte[255];
            int count = receiveStream.Read(bf, 0, 255);
            while (count > 0)
            {
                mStream.Write(bf, 0, count);
                count = receiveStream.Read(bf, 0, 255);
            }
            receiveStream.Close();

            mStream.Seek(0, SeekOrigin.Begin);

            //从内存流里读取字符串
            StreamReader reader = new StreamReader(mStream, encode);
            char[] buffer = new char[1024];
            count = reader.Read(buffer, 0, 1024);
            while (count > 0)
            {
                str += new String(buffer, 0, count);
                count = reader.Read(buffer, 0, 1024);
            }

            //从解析出的字符串里判断charset，如果和http应答的编码不一直
            //那么以页面声明的为准，再次从内存流里重新读取文本
            Regex reg =
             new Regex(@"<meta[/s/S]+?charset=(.*)""[/s/S]+?>",RegexOptions.Multiline | RegexOptions.IgnoreCase);
            MatchCollection mc = reg.Matches(str);
            if (mc.Count > 0)
            {
                string tempCharSet = mc[0].Result("$1");
                if (string.Compare(tempCharSet, characterSet, true) != 0)
                {
                    encode = Encoding.GetEncoding(tempCharSet);
                    str = string.Empty;
                    mStream.Seek(0, SeekOrigin.Begin);
                    reader = new StreamReader(mStream, encode);
                    buffer = new char[255];
                    count = reader.Read(buffer, 0, 255);
                    while (count > 0)
                    {
                        str += new String(buffer, 0, count);
                        count = reader.Read(buffer, 0, 255);
                    }
                }
            }
            reader.Close();
            mStream.Close();
        }
    }
    catch (Exception ex)
    {
        Trace.TraceError(ex.ToString());
    }
    finally
    {
        if (response != null)
            response.Close();
    }
    return str;//返回的源码，你自己检索你想要的行吧。
}