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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.

QueryString Out of Encoded URL

I have an encoded URL.
http%3a%2f%myurl.test.me%2fSometjing%2fProduct%2fSearch%3fq=Tomato
I am trying to get query string out of the url which is "Tomato". I am using the following code but it returns null.
var parsedQuery = HttpUtility.ParseQueryString((url));
Console.Write(parsedQuery["q"]); // null

You're missing a few steps. You need to decode the URL, then pull out the query string, and then parse the query string:
string decoded =
HttpUtility.UrlDecode("http%3a%2f%2fmyurl.test.me%2fSometjing%2fProduct%2fSearch%3fq=Tomato");
var uri = new Uri(decoded);
var parsedQuery = HttpUtility.ParseQueryString(uri.Query);
Console.WriteLine (parsedQuery["q"]); // Tomato
Also, your encoded URL is a little malformed. The one in your post decoded looks like this:
http:/%myurl.test.me/Sometjing/Product/Search?q=Tomato
I think you just missed a 2f after the % right before myurl.test:
http%3a%2f%2fmyurl.test.me%2fSometjing%2fProduct%2fSearch%3fq=Tomato

The URL needs to decoded first before you can use the HttpUtility.ParseQueryString().
Fair warning though mentioned directly from MSDN.
The ParseQueryString method uses query strings that might contain user input, which is a potential security threat. By default, ASP.NET Web pages validate that user input does not include script or HTML elements. MSDN.

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();
}

Add incoming querystring to all outgoing links/traffic c#

If i have a page called www.testsite.com and I link to that page using a querystring in the url, is it possible to attach that same querystring to all the outgoing links/traffic somehow?
For instance, say I link to that page like this www.testsite.com?parameter1=somevalue
And then, on that page I click a link to for instance google, and I would like the parameter to be passed so the url would be www.google.com?parameter1=somevalue.
I know how to do this manually, but is there someway it can be appended to the url automatically? Like catch the outgoing request before happening and add the parameter?
Thanks!
Eric

you could do this pretty simply with javascript or javascript using jQuery
$("a").click(function(e){
e.preventDefault();
window.location = $(this).attr("href") + window.location.search;
});
that should get you started
if you wanted a non-jQuery solution you can look into binding events using javascript only
http://www.digimantra.com/tutorials/change-onclick-function-anchor-tag-javascript/
http://forums.techarena.in/software-development/1308647.htm

You can implement an intercepting filter through an httpmodule which modifies the html you emit back to the client. For more details see: http://msdn.microsoft.com/en-us/library/ff649096.aspx
And a few more examples:
Http Response Filter
SO: Get HTML content for modification

Unless you have a central location where you output the outgoing links, you will have to do this manually (possibly the visual studio search/replace can help here, but I would be careful as you may end up changing links you didn't want to).

You can use following to use Query String parameters
You can loop through all your query string parameters like this
int loop1, loop2;
// Load NameValueCollection object.
NameValueCollection coll = Request.QueryString;
// Get names of all keys into a string array. String[] arr1 = coll.AllKeys;
string parameters = "";
for (loop1 = 0; loop1 < arr1.Length; loop1++)
{
parameters += Server.HtmlEncode(arr1[loop1]) + "=" + coll.GetValues(arr1[loop1]);
for (loop2 = 0; loop2 < arr2.Length; loop2++)
{
parameters += Server.HtmlEncode(arr2[loop2]);
}
}
its just basic idea. But you can loop through parameters without knowing the names.

C# HTTP programming

i want to build a piece of software that will process some html forms, the software will be a kind of bot that will process some forms on my website automatically.
Is there anyone who can give me some basic steps how to do this job...Any tutorials, samples, books or whatever can help me.
Can some of you post an working code with POST method ?

Check out How to: Send Data Using the WebRequest Class. It gives an example of how create a page that posts to another page using the HttpWebRequest class.

To fill out the form...
Find all of the INPUT or TEXTAREA elements that you want to fill out.
Build the data string that you are going to send back to the server. The string is formatted like "name1=value1&name2=value2" (just like in the querystring). Each value will need to be URL encoded.
If the form's "method" attribute is "GET", then take the URL in the "action" attribute, add a "?" and the data string, then make a "GET" web request to the URL.
If the form's "method" is "POST", then the data is submitted in a different area of the web request. Take a look at this page for the C# code.

To expand on David and JP's answers':
Assuming you're working with forms whose contents you're not familiar with, you can probably...
pull the page with the form via an HttpWebRequest.
load it into an XmlDocument
Use XPath to traverse/select the form elements.
Build your query string/post data based on the elements.
Send the data with HttWebRequest
If the form's structure is known in advance, you can really just start at #4.
(untested) example (my XPath is not great so the syntax is almost certainly not quite right):
HttpWebRequest request;
HttpWebResponse response;
XmlDocument xml = new XmlDocument();
string form_url = "http://...."; // you supply this
string form_submit_url;
XmlNodeList element_nodes;
XmlElement form_element;
StringBuilder query_string = new StringBuilder();
// #1
request = (HttpWebRequest)WebRequest.Create(form_url));
response = (HttpWebResponse)request.GetResponse();
// #2
xml.Load(response.GetResponseStream());
// #3a
form_element = xml.selectSingleNode("form[#name='formname']");
form_submit_url = form_element.GetAttribute("action");
// #3b
element_nodes = form_element.SelectNodes("input,select,textarea", nsmgr)
// #4
foreach (XmlNode input_element in element_nodes) {
if (query_string.length > 0) { query_string.Append("&"); }
// MyFormElementValue() is a function/value you need to provide/define.
query_string.Append(input_element.GetAttribute("name") + "=" + MyFormElementValue(input_element.GetAttribute("name"));
}
// #5
// This is a GET request, you can figure out POST as needed, and deduce the submission type via the <form> element's attribute.
request = (HttpWebRequest)WebRequest.Create(form_submit_url + "?" + query_string.ToString()));
References:
Link
http://www.developerfusion.com/forum/thread/26371/
http://msdn.microsoft.com/en-us/library/system.xml.xmlelement.getattribute.aspx
http://msdn.microsoft.com/en-us/library/system.xml.xmlelement.selectnodes.aspx

If you don't want to go the HttpWebRequest route, I would suggest WatiN. Makes it very easy to automate IE or Firefox and not worry about the internals of the HTTP requests.