C# web request with POST encoding question

Question

On the MSDN site there is an example of some C# code that shows how to make a web request with POST'ed data. Here is an excerpt of that code:

WebRequest request = WebRequest.Create ("http://www.contoso.com/PostAccepter.aspx ");
request.Method = "POST";
string postData = "This is a test that posts this string to a Web server.";
byte[] byteArray = Encoding.UTF8.GetBytes (postData); // (*)
request.ContentType = "application/x-www-form-urlencoded";
request.ContentLength = byteArray.Length;
Stream dataStream = request.GetRequestStream ();
dataStream.Write (byteArray, 0, byteArray.Length);
dataStream.Close ();
WebResponse response = request.GetResponse ();
...more...

The line marked (*) is the line that puzzles me. Shouldn't the data be encoded using the UrlEncode function than UTF8? Isn't that what application/x-www-form-urlencoded implies?

Answer 1

The sample code is misleading, because ContentType is set to application/x-www-form-urlencoded but the actual content is plain text. application/x-www-form-urlencoded is a string like this:

name1=value1&name2=value2

The UrlEncode function is used to escape especial characters like '&' and '=' so a parser doesn't consider them as syntax. It takes a string (media type text/plain) and returns a string (media type application/x-www-form-urlencoded).

Encoding.UTF8.GetBytes is used to convert the string (media type application/x-www-form-urlencoded in our case) into an array of bytes, which is what the WebRequest API expects.

Answer 2

As Max Toro indicated, the examples on the MSDN site are incorrect: a correct form POST requires the data to be URL encoded; since the data in the MSDN example does not contain any characters that would be changed by encoding, they are, in a sense, already encoded.

The correct code would have a System.Web.HttpUtility.UrlEncode call on the names and values of each name/value pair before combining them into the name1=value1&name2=value2 string.

This page was helpful: http://geekswithblogs.net/rakker/archive/2006/04/21/76044.aspx