You're looking at a compressed byte stream. You can tell by inspecting the headers of the http response, for example with curl:
curl -X HEAD -i http://bet.hkjc.com/
but the Developer Console of your browser will reveal the same:
HTTP/1.1 200 OK
Cache-Control: public, max-age=120, must-revalidate
Content-Length: 3615
Content-Type: text/html; charset=utf-8
Content-Encoding: gzip
Expires: Wed, 29 Jun 2016 08:01:06 GMT
Vary: Accept-Encoding
Server: Microsoft-IIS/7.0
X-AspNet-Version: 2.0.50727
X-Powered-By: ASP.NET
Date: Wed, 29 Jun 2016 08:00:14 GMT
Via: 1.1 stjbwbwa52
Accept-Ranges: bytes
Notice the Content-Encoding: to say gzip. This means the result you just got is compressed with the gzip algorithm. The standard WebClient can't handle that but with an simple subclass the WebClient can do new tricks:
public class DecompressWebClient:WebClient
{
// moved common logic here
public DecompressWebClient()
{
this.Encoding = Encoding.UTF8;
}
// This is the factory to create the webrequest
protected override WebRequest GetWebRequest(Uri address)
{
// get the default one
var request = base.GetWebRequest(address);
// see if it is a HttpWebRequest
var httpReq = request as HttpWebRequest;
if (httpReq != null)
{
// add extra capabilities, like decompression
httpReq.AutomaticDecompression = DecompressionMethods.GZip;
}
return request;
}
}
On the HttpWebRequest there exists a property AutomaticDecompression that, when set to true, will take care of the decompression for us.
When you put the Subclassed WebClient to use your code will look like:
string url = "http://bet.hkjc.com";
using(WebClient webClient = new DecompressWebClient())
{
string html = webClient.DownloadString(url);
File.WriteAllText("page.html", html);
}
The encoding UTF8 is correct, as you can also see in the header for the Content-Type setting.
The top of the html file will look like this:
<html>
<head>
<meta http-equiv="X-UA-Compatible" content="IE=EmulateIE7; IE=EmulateIE10"/>
<meta name="application-name" content="香港賽馬會"/>
<title>香港賽馬會</title>
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