Question

I searched SO and found similar questions, but none compared all three. That surprised me, so if someone knows of one, please point me to it.

There are a number of different ways to parse the query string of a request… the “correct” way (IMO) should handle null/missing values, but also decode parameter values as appropriate. Which of the following would be the best way to do both?

Method 1

string suffix = Request.QueryString.Get("suffix") ?? "DefaultSuffix";

Method2

string suffix = Request.QueryString["suffix"] ?? "DefaultSuffix";

Method 3

NameValueCollection params = HttpUtility.ParseQueryString(Request.RawUrl);    
string suffix = params.Get("suffix") ?? "DefaultSuffix";

Method 4

NameValueCollection params = HttpUtility.ParseQueryString(Request.RawUrl);    
string suffix = params["suffix"] ?? "DefaultSuffix";

Questions:

1. Would Request.QueryString["suffix"] return a null if no suffix was specified?
   (Embarrassingly basic question, I know)

2. Does HttpUtility.ParseQueryString() provide any extra functionality over accessing Request.QueryString directly?

3. The MSDN documentation lists this warning:

   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. For more information, see Script Exploits Overview.

   But it’s not clear to me if that means ParseQueryString() should be used to handle that, or is exposed to security flaws because of it… Which is it?

4. ParseQueryString() uses UTF8 encoding by default… do all browsers encode the query string in UTF8 by default?

5. ParseQueryString() will comma-separate values if more than one is specified… does Request.QueryString() do that as well, or what happens if it doesn’t?

6. Which of those methods would correctly decode “%2b” to be a “+”?

Showing my Windows development roots again… and I would be a much faster developer if I didn’t wonder about these things so much… : P

Answer 1

Methods #1 and #2 are the same thing, really. (I think the .Get() method is provided for language compatibility.)

ParseQueryString returns you something that is the functional equivalent of Request.Querystring. You would usually use it when you have a raw URL and no other way to parse the query string parameters from it. Request.Querystring does that for you, so in this case, it’s not needed.

1. You can’t leave off "suffix". You either have to pass a string or an index number. If you leave off the [] entirely, you get the whole NameValueCollection. If you mean what if "suffix" was not one of the QueryString values then yes; you would get null if you called Request.QueryString["suffix"].

2. No. The most likely time you would use it is if you had an external URL and wanted to parse the query string parameters from it.

3. ParseQueryString does not handle it… neither does pulling the values straight from Request.QueryString. For ASP.NET, you usually handle form values as the values of controls, and that is where ASP.NET usually ‘handles’ these things for you. In other words: DON’T TRUST USER INPUT Ever. No matter what framework is doing what ever for you.

4. I have no clue (I think no). However, I think what you are reading is telling you that ParseQueryString is returning UTF-8 encoded text – regardless if it was so encoded when it came in.

5. Again: ParseQueryString returns basically the same thing you get from Request.QueryString. In fact, I think ParseQueryString is used internally to provide Request.QueryString.

6. They would produce the equivalent; they will all properly decode the values submitted. If you have URL: http://site.com/page.aspx?id=%20Hello then call Request.QueryString["id"] the return value will be " Hello", because it automatically decodes.