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C# Percentage Decoding

I am trying to decode a percentage encoded string passed from a PHP script to my C# application. The PHP encrypts the data, so there are many special characters that I percentage encode.
Here's the string I'm passing in the URL:
%C9%90%04L%EFEA%D1U%AFi%CBc%3A%E5%D0%40Q%D6%1Bn%C9%C3%B5%0FT%FC%E5h%95m%EF%BF%24tB%A6%D1%08%3B%83%A1%CF%1B%99Zo%02
But it has trouble percentage decoding parts of it: when I fetch the query string, like so:
var queryString = HttpContext.Current.Request.QueryString;
var token = queryString["token"];
The variable token, though, equals this:
%C9%90%04L%EF%BF%BDEA%EF%BF%BDU%EF%BF%BDI%EF%BF%BDC%3A%EF%BF%BD%EF%BF%BD%40Q%EF%BF%BD%1BN%EF%BF%BD%C3%B5%0FT%EF%BF%BD%EF%BF%BDH%EF%BF%BDM%EF%BF%BD%24TB%EF%BF%BD%EF%BF%BD%08%3B%EF%BF%BD%EF%BF%BD%EF%BF%BD%1B%EF%BF%BDZO%02
This is definitely not what I put into the query string. When looking at it, the first time it messes up is %EF(starts 11th character into the original query string). Instead of %EF it shows: %EF%BF%BD. When I searched a little, I found this webpage which says the "Hex UTF-8 Bytes" are EF BF BD.
EDIT:
Forgot to mention, QueryString looks like this:
token=%c9%90%04L%ef%bf%bdEA%ef%bf%bdU%ef%bf%bdi%ef%bf%bdc%3a%ef%bf%bd%ef%bf%bd%40Q%ef%bf%bd%1bn%ef%bf%bd%c3%b5%0fT%ef%bf%bd%ef%bf%bdh%ef%bf%bdm%ef%bf%bd%24tB%ef%bf%bd%ef%bf%bd%08%3b%ef%bf%bd%ef%bf%bd%ef%bf%bd%1b%ef%bf%bdZo%02&oauth_token_secret=S%23%2bw%ef%bf%bd%ef%bf%bdX%17%ef%bf%bd0%ef%bf%bd%60%ef%bf%bd%ef%bf%bd%ef%bf%bd%ef%bf%bd*%ef%bf%bdi%08%ef%bf%bd%ef%bf%bd%ef%bf%bd%ef%bf%bd%07%ef%bf%bd%12RS07%ef%bf%bdgl%1e%ef%bf%bd%d7%832%d1%a1%ef%bf%bd%275%ef%bf%bdv%ef%bf%bd

You might be looking for the HttpServerUtility.UrlDecode method:
HttpContext.Current.Server.UrlDecode(HttpContext.Current.Request.QueryString["token"]);

Your error is somewhere else...
I created a new web page in a .Net 4.0 project, and put this in the Page_Load:
protected void Page_Load(object sender, EventArgs e)
{
var queryString = HttpContext.Current.Request.QueryString;
var token = queryString["token"];
throw new Exception(token);
}
Then I ran the page by going to this URL which matches the querystring you gave above:
http://localhost:27151/test.aspx?token=%c9%90%04L%ef%bf%bdEA%ef%bf%bdU%ef%bf%bdi%ef%bf%bdc%3a%ef%bf%bd%ef%bf%bd%40Q%ef%bf%bd%1bn%ef%bf%bd%c3%b5%0fT%ef%bf%bd%ef%bf%bdh%ef%bf%bdm%ef%bf%bd%24tB%ef%bf%bd%ef%bf%bd%08%3b%ef%bf%bd%ef%bf%bd%ef%bf%bd%1b%ef%bf%bdZo%02
The page decoded the token and displayed it in the exception message as this:
ɐL�EA�U�i�c:��#Q�n�õT��h�m�$tB��;����Zo
(The URL is encoding a binary string so when the actual string is printed, there are some characters that don't get displayed.)
If you run this and the token actually prints "%C9%90%04L..." then your token has probably been double encoded. All of the percent signs will be replaced with "%25" so your URL would look like this:
http://localhost:27151/test.aspx?token=%25c9%2590%2504L%25ef%25bf%25bdEA%25ef%25bf%25bdU%25ef%25bf%25bdi%25ef%25bf%25bdc%253a%25ef%25bf%25bd%25ef%25bf%25bd%2540Q%25ef%25bf%25bd%251bn%25ef%25bf%25bd%25c3%25b5%250fT%25ef%25bf%25bd%25ef%25bf%25bdh%25ef%25bf%25bdm%25ef%25bf%25bd%2524tB%25ef%25bf%25bd%25ef%25bf%25bd......
Since you didn't mention the "%25", the error is somewhere else in your code. The URL you think you are using is not the one being decoded.

How can I pass an url as value on a querystring and then get it back as plain text

I wonder if I would have encoding problems with the code below, I just need to know the url in querystring, and how can I retrieve it back without enconding problems.
string currentWebUrl = SPContext.Current.Web.Url;
string fullLink = String.Format("{0}?ClientCode={1}&ClientSiteCode={2}&currenturl={3}",
Link, ClientCode,
clientSiteCode, currentWebUrl);

Yes, the URL will appear encoded in the address bar, but that should be fine.
When you want to retrieve it without the encoding you can use HttpUtility.UrlDecode.
For example:
string qs = HttpUtility.UrlDecode(Request.QueryString["currenturl"].ToString());

Request.Url.GetLeftPart(UriPartial.Path)

How do I send a URL with Query Strings as a Query String

I am doing a redirect from one page to another and another redirect from the second page to a third. I have imformation from the first page which is not used on the second page but must be transfered to the third page. Is it possible to send the URL of the third page with its Query Strings as a Query String to the second page. Here's an example:
Response.Redirect("MyURL1?redi=MyURL2?name=me&ID=123");
My problem is that the URL being sent as a Query String has two Query String variables, so how will the system know that what's after the & is the second variable of the second URL and not a second variable of the first URL? Thank you.

You must encode the url that you pass as a parameter in your redirect URL. Like this:
MyURL = "MyURL1?redi=" + Server.UrlEncode("MyURL2?name=me&ID=123");
This will create a correct url without the double '?' and '&' characters:
MyURL1?redi=MyURL2%3fname%3dme%26ID%3d123
See MSDN: HttpServerUtility.UrlEncode Method
To extract your redirect url from this encoded url you must use HttpServerUtility.UrlDecode to turn it into a correct url again.

Your query string should look like this:
MyURL1?redi=MyURL2&name=me&ID=123
Check: http://en.wikipedia.org/wiki/Query_string
You should have one ? sign and all parameters joined with &. If parameter values contain special characters just UrlEncode them.

I find it helpful to encode query string parameters in Base64 before sending. In some cases this helps, when you need to send all kinds of special characters. It doesn't make for good debug strings, but it will protect ANYTHING you are sending from getting mixed with any other parameters.
Just keep in mind, the other side who is parsing the query string will also need to parse the Base64 to access the original input.

using System.IO;
using System.Net;
static void sendParam()
{
// Initialise new WebClient object to send request
var client = new WebClient();
// Add the QueryString parameters as Name Value Collections
// that need to go with the HTTP request, the data being sent
client.QueryString.Add("id", "1");
client.QueryString.Add("author", "Amin Malakoti Khah");
client.QueryString.Add("tag", "Programming");
// Prepare the URL to send the request to
string url = "http://026sms.ir/getparam.aspx";
// Send the request and read the response
var stream = client.OpenRead(url);
var reader = new StreamReader(stream);
var response = reader.ReadToEnd().Trim();
// Clean up the stream and HTTP connection
stream.Close();
reader.Close();
}

How to read the query string when it contains unencoded data?

I have the below asp.net page which accepts a "url" query string key whose value can be an un-encoded url:
http://localhost:4104/WebSiteForTest/TinyUrl.aspx?url=http://www.google.co.uk/#hl=en&q=life&oq=life&aq=f&aqi=g-s1g9&aql=&gs_sm=3&gs_upl=2803373l2803701l2l2803826l4l4l0l0l0l0l188l453l0.3l3l0&bav=on.2,or.r_gc.r_pw.r_cp.,cf.osb&fp=94681dc4659502d1&biw=1680&bih=883
Now from this page, how would that be possible to read the text after ".aspx?"?
I checked the Request.Url.AbsoluteUri property and it only showed
"http://localhost:4104/WebSiteForTest/TinyUrl.aspx?url=http://www.google.co.uk/"
I also checked with the Request.QueryString with the below code:
private void getQueryString()
{
var sb = new StringBuilder();
var queryStringCount = Request.QueryString.Keys.Count;
for (int keyIndex = 0; keyIndex < queryStringCount; keyIndex++)
{
sb.Append(Request.QueryString.Keys[keyIndex]).Append("=").Append(Request.QueryString[keyIndex]);
if (keyIndex != (queryStringCount - 1))
{
sb.Append("&");
}
}
}
However, the code after "#" doesn't appear in any query string.
how would that be possible to read the text after ".aspx?"?
if you say it's not possible, how Google uses "#" in their url then when you search for something?!
http://www.google.co.uk/#hl=en&site=&q=life&oq=life&aq=f&aqi=g-s1g9&aql=&gs_sm=3&gs_upl=3317l3630l0l3755l4l4l0l0l0l0l125l391l3.1l4l0&bav=on.2,or.r_gc.r_pw.r_cp.,cf.osb&fp=94681dc4659502d1&biw=1680&bih=849
Thanks,

It's not possible to get value after anchor on server side, you can check this with fiddler or something similar, you should deal with this on client. Browser simply strips all after anchor.
Retrieving Anchor Link In URL for ASP.Net
c# get complete URL with "#"
Update:
I don't know how google exactly do this, but if you look with fiddler after initial request there goes another without #, here is a fidller log for request from your question :
so my advice is look with fiddler how google do this, or maybe ask another question

Use Request.QueryString
http://localhost:4104/WebSiteForTest/TinyUrl.aspx?url=http://www.google.co.uk/#hl=en&q=life&oq=life&aq=f&aqi=g-s1g9&aql=&gs_sm=3&gs_upl=2803373l2803701l2l2803826l4l4l0l0l0l0l188l453l0.3l3l0&bav=on.2,or.r_gc.r_pw.r_cp.,cf.osb&fp=94681dc4659502d1&biw=1680&bih=883
<%=Request.QueryString("url")%> will get the ?url parameter

I assume you're using C# to do this. You can easily get the parameters and their values by iterating through the request object. Or in this case, since you know the name of the parameter, simply do this:
String url = Request.QueryString["url"];
More information on iterating through your request parameters can be found here.

The Uri Type works as well.
String yourHttpUri ="....";
Uri yourURI = new Uri(yourHttpUri);
yourURI.query // "?url=http://www.google.co.uk/"
yourURI.fragment // "#hl=en&q=life&oq=life&aq=f&aqi=g-s1g9&aql=&gs_sm=3&gs_upl=2803373l2803701l2l2803826l4l4l0l0l0l0l188l453l0.3l3l0&bav=on.2,or.r_gc.r_pw.r_cp.,cf.osb&fp=94681dc4659502d1&biw=1680&bih=883"
Edit:
Have you tried Request.Url.ToString(); (And create a new Uri from the result)

WebBrowser keep url/uri encoded dont decode

I have a web-browser in a win form application and I am experiencing issues when opening a URL.
The URL I pass in as a new URL instance is encoded with:
/ as %2f , ? as %3f and the
= as %3d
But when I debug my code I can see that the absolute URL or any of the other ones in the webbrowser.url.* is decoded as / , ? and =.
How do I keep the URL encoded? The URL will not work if It is not encoded like that.

I found a solution to my problem, when you have a URL that looks something like this:
domain.com/action/doaction/?identity=12354698789
And you want it encoded like this:
domain.com/logon?returnurl=action%2fdoaction%2f%3fidentity%3d12354698789
That does not work in your web browser. It decodes it to the first url.
I needed the id in the doaction controller so I used this code:
string orgId = ControllerContext.RouteData.Values["id"].ToString();
It returns that url, if unsure, debug and trace through, you will find the right key and value.

Why is it a problem?
If you want the undecoded URL, use the HttpRequest.RawUrl Property. The query string is automatically decoded by default and there is no public parameter that would turn it off.