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Can I allow raw unicode in HTTP headers using NSUrlSession?

I'm constructing an NSUrlSession as follows:
NSUrlSessionConfiguration sessionCfg = NSUrlSessionConfiguration.CreateBackgroundSessionConfiguration("mySpecialSessionName");
NSUrlSessionDelegate sessionDelegate = new MySessionDelegate();
urlSession = NSUrlSession.FromConfiguration(sessionCfg, sessionDelegate, NSOperationQueue.MainQueue);
And invoking background downloads with custom HTTP headers:
NSMutableUrlRequest mutableRequest = new NSMutableUrlRequest();
mutableRequest.HttpMethod = "POST";
mutableRequest.Url = NSUrl.FromString(someEndpoint);
mutableRequest["MyCustomHeader"] = someStringWithUnicodeChars;
mutableRequest.Body = NSData.FromString(somePostBody);
NSUrlSessionDownloadTask downloadTask = m_UrlSession.CreateDownloadTask(mutableRequest);
downloadTask.Resume();
However, the header value string seems to get truncated at the first character above 255. For example, the header value:
SupeЯ Σario Bros
is received by the server as
Supe
When instead using .NET HttpClient on xamarin, unicode header strings successfully make it to the server unmodified. However, I'd like to make use of NSUrlSession's background downloading feature.
(I realize that support of unicode in HTTP headers is hit-and-miss, but since the HTTP server in this case is a particular custom server that doesn't currently support things like base64 encoding, passing the raw string is desired)

I don't know whether you'll be able to make that work, but two things come to mind:
What you have here is equivalent to calling setValue:forKey: on the URL request. I don't think that will do what you're expecting. Try calling the setValue:forHTTPHeaderField: method instead.
Try specifying the encoding before you specify your custom header value, e.g. [theRequest setValue:#"...; charset=UTF-8" forHTTPHeaderField:#"Content-Type"];
If neither of those helps, you'll probably have to encode the data in some way. I would suggest using URL encoding, because that's a lot simpler to implement on the server side than Base64. For the iOS side, see this link for info on how to URL-encode a string:
https://developer.apple.com/library/mac/documentation/Cocoa/Conceptual/URLLoadingSystem/WorkingwithURLEncoding/WorkingwithURLEncoding.html

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.

German characters sending data using POST method from ASP page to PHP page

I have a problem with sending data from ASP with the POST Method to a PHP page.
I would like to send mail with names. And since I live in Austria the names are in German and we have some Special characters. These characters don't arrive write.
I'm still pretty new to programming with C# btw. I had the Website before in Java-Script but I had to connect it with a database and therefore I switched to C# and now I'm like a "babe in the woods".
this.hdnDaten.Value = "ÄÖÜ|äöü|ß|é|#";
// mit POST versuchen
using (var client = new WebClient())
{
var postData = new System.Collections.Specialized.NameValueCollection();
postData.Add("von", this.hdnVon.Value);
postData.Add("an", this.hdnAn.Value);
postData.Add("betreff", this.hdnBetreff.Value);
postData.Add("daten", this.hdnDaten.Value);
byte[] response = client.UploadValues("http://xxxxxx.php", "POST", postData);
var responsebody = Encoding.UTF8.GetString(response);
}
And this is how the characters (in this.hdnDaten.Value) from above arrive in the mail-body:
ÄÖÜ|äöü|ß|é|#
Does anybody know what I can do to get the same characters in the end?
Edit 20143013: I think I have a clue: I have to encode the postData into ANSI (Codepage 1252). I tried do do this, but it doesn't work. Does anybody have an Idea how I could do this?
Edit 20140320: I don't even dare to give you the answer: I was looking all the time in the wrong place (somewhat like MH370): The problem was with the receiving side of the mail (I was using a POP3-Viewer for testing); when I downloaded the mail to Outlook everything was OK. The funny thing was that this didn't happen in the original (Javascript) Version that's why I was looking at the wrong place.
Thanks
Eddie

Try setting client.Encoding to UTF-8 before calling UploadValues. Also ensure that you read the text as UTF-8 on the server.

Try this.hdnDaten.Value = HttpUtility.UrlEncode("ÄÖÜ|äöü|ß|é|#"); on your post parameters.
on PHP you'll need to decode the parameters via html_entity_decode

Box API v2 creating folder with cyrillic letters in it's name

I'm trying to create folder using new API.
If folder name contains cyrillic letters, I receive HTTP 400 Bad Request.
However it works fine with latin letters.
Is it known issue?

I found correct answer here: Detecting the character encoding of an HTTP POST request
the default encoding of a HTTP POST is ISO-8859-1.
The only thing I need is to manually set encoding of the request.
By the way, here is working code:
public static Task<string> Post(string url, string data, string authToken) {
var client = new WebClient { Encoding = Encoding.UTF8 };
client.Headers.Add("Content-Type:application/x-www-form-urlencoded");
client.Headers.Add(AuthHeader(authToken));
return client.UploadStringTaskAsync(new Uri(url), "POST", data);
}

Usually, complications involving international characters in Box API calls just need minor adjustments to the encoding of the requests. I'm guessing you'll just have to encode the target folder name with a urlencode.
If that doesn't do the trick, we may be able to help more if you send a sample request or code snippet. If you do, keep the api key and auth token to yourself.

Encoding non UTF-8 text in Parameters in ASP.NET MVC

Background
I have a web application that uses ISO-8859-1 encoding. When I pass parameters using Html.ActionLink(), the value is decoded to UTF-8:
Web.config:
<globalization requestEncoding="iso-8859-1" responseEncoding="iso-8859-1"
fileEncoding="iso-8859-1" />
Index.aspx
This is a <%= Html.ActionLink("test", "Read", new { name="Cosméticos" }) %>
generates the following:
This is a test
The problem is the value I receive in my controller is UTF-8, not iso-8859-1:
TestController:
public ActionResult Read(string name) {
//name is "Cosméticos" here!
}
Question
Why the string is not decoded to Cosméticos?

Does your aspx files are physically saved in iso-8859-1?
"File / Save Xyz As" And click at the right of the save button to have more encoding options to save your file in..
A guess

public static string ActionLinkNoEncode(this HtmlHelper htmlHelper, string linkText, ActionResult action )
{
var urlHelper = new UrlHelper(htmlHelper.ViewContext.RequestContext);
var url = Uri.UnescapeDataString(urlHelper.Action(action)).ToLowerInvariant();
var linkTagBuilder = new TagBuilder("a");
linkTagBuilder.MergeAttribute("href", url);
linkTagBuilder.InnerHtml = linkText;
return linkTagBuilder.ToString();
}

I found the problem and the workaround: the value I receive is UTF-8, but if I try to use System.Text.Encoding.UTF8.GetBytes(name) it converts the characters "é" to UTF-8 values instead of "É".
The workaround is to copy the string to a byte[] and then use System.Text.Encoding.Convert().
I don't know if this is the best way, but now everything is working for me.

A few things you might want to consider.
First, if you haven't already read it -- I highly recommend reading Joel Spolsky's article 'The Absolute Minimum Every Software Developer Absolutely, Positively Must Know About Unicode and Character Sets (No Excuses!)' It sets the stage for learning about character encoding and programming.
Second, looking at the docs on the globalization element in the web.config it sounds like there are ways to (accidentally?) override the specified encoding scheme. From the docs:
requestEncoding
Specifies the assumed encoding of each incoming request, including
posted data and the query string. If the request comes with a request
header containing an Accept-Charset attribute, it overrides the
requestEncoding in configuration. The default encoding is UTF-8,
specified in the <globalization> tag included in the Machine.config
file created when the .NET Framework is installed. If request encoding
is not specified in a Machine.config or Web.config file, encoding
defaults to the computer's Regional Options locale setting. In
single-server applications, requestEncoding and responseEncoding
should be the same. For the less common case (multiple-server
applications where the default server encodings are different), you
can vary the request and response encoding using local Web.config
files.
Have you tried using something like Fiddler to see what the Accept-Charset attribute is set to?