Losing characters in web based string parsing using query strings

Question

Hi, I am trying to request a webpage from an iis web server that I control utilising query strings.

E.g., I have a webbrowser control in my winforms app and request a page similar to "www.site.com/getpage.ashx?field=afsfgwesar+sere"

When i try to run this it fails because on the server side, getpage.ashx can’t locate the right field.

After much hair pulling I have figured out that the string has actually changed from what was sent to the browser and what was received - i.e. - the plus symbol is missing when the server starts working with it.

It begins as "afsfgwesar+sere" and ends as "afsfgwesarsere". So somewhere along the line the string is being reformatted?

This is how I am getting the string on the server side -

string field = (string)context.Request.QueryString["field"];

It is at this point I have stepped in and seen the missing plus symbol.

Does anyone know why I am losing the plus symbol and how I can get it back?

Answer 1

The + symbol is replaced with a space character because spaces are not allowed characters.

You can insert %2B to "get" the plus symbol after the URL is decoded.

www.site.com/getpage.ashx?field=afsfgwesar%2Bsere

The HttpUtility class has methods to URL encode and decode strings. To see what it basically does, there is also an online encoder/decoder which you can use.

Answer 2

The plus sign is a reserved character in querystrings. It is often interpreted as a space character. Just have a look at a search engine and you'll notice this.

You can prevent this by encoding the afsfgwesar+sere text before adding it to the querystring. Use HttpUtility.UrlEncode to do so. Use HttpUtility.UrlDecode to read it back.

For more info, read: http://msdn.microsoft.com/en-us/library/4fkewx0t.aspx