Asp.net httpwebrequest automatically identifies webpage Encoding

CopyCode The Code is as follows: static string getencoding (string URL)
{
Httpwebrequest request = NULL;
Httpwebresponse response = NULL;
Streamreader reader = NULL;
Try
{
Request = (httpwebrequest) webrequest. Create (URL );
Request. Timeout = 20000;
Request. allowautoredirect = false;

Response = (httpwebresponse) request. getresponse ();
If (response. statuscode = httpstatuscode. OK & response. contentlength <1024*1024)
{
If (response. contentencoding! = NULL & response. contentencoding. Equals ("gzip", stringcomparison. invariantcultureignorecase ))
Reader = new streamreader (New gzipstream (response. getresponsestream (), compressionmode. Decompress ));
Else
Reader = new streamreader (response. getresponsestream (), encoding. ASCII );

String html = reader. readtoend ();

RegEx reg_charset = new RegEx (@ "charset \ B \ s * = \ s *(? <Charset> [^ ""] *) ");
If (reg_charset.ismatch (HTML ))
{
Return reg_charset.match (HTML). Groups ["charset"]. value;
}
Else if (response. characterset! = String. Empty)
{
Return response. characterset;
}
Else
Return encoding. Default. bodyname;
}
}
Catch
{
}
Finally
{

If (response! = NULL)
{
Response. Close ();
Response = NULL;
}
If (reader! = NULL)
Reader. Close ();

If (request! = NULL)
Request = NULL;

}

Return encoding. Default. bodyname;
}

/// <Summary>
/// ObtainSource code
/// </Summary>
/// <Param name = "url"> </param>
/// <Returns> </returns>
Static string gethtml (string URL, encoding)
{
Httpwebrequest request = NULL;
Httpwebresponse response = NULL;
Streamreader reader = NULL;
Try
{
Request = (httpwebrequest) webrequest. Create (URL );
Request. Timeout = 20000;
Request. allowautoredirect = false;

Response = (httpwebresponse) request. getresponse ();
If (response. statuscode = httpstatuscode. OK & response. contentlength <1024*1024)
{
If (response. contentencoding! = NULL & response. contentencoding. Equals ("gzip", stringcomparison. invariantcultureignorecase ))
Reader = new streamreader (New gzipstream (response. getresponsestream (), compressionmode. Decompress), encoding );
Else
Reader = new streamreader (response. getresponsestream (), encoding );
String html = reader. readtoend ();

Return HTML;
}
}
Catch
{
}
Finally
{

If (response! = NULL)
{
Response. Close ();
Response = NULL;
}
If (reader! = NULL)
Reader. Close ();

If (request! = NULL)
Request = NULL;

}

Return string. empty;
}