How does Stackoverflow escape tag names in urls

Question

I want to generate a url from a tag name.

In my view (asp.net mvc) I have the following:

<%= Html.ActionLink(Html.Encode(tagName), 
"tagged" //action, 
"posts" //controller, 
new {tagName=Html.UrlEncode(tagName)} //querystring argument, 
new {@class="tag"} //html attributes) 
%>

But this generates the following URL if the tagName is "c#" (without the quotes):

http://localhost/posts/tagged/c%2523

which results in Http 400 error - Bad Request

On Stackoverflow, the url for the same "c#" tag generates "c%23" instead of "c%2523"

I tried Html.UrlEncode, Uri.EscapeDataString, Uri.EscapeUrlString, but none of those produces the desirable "c%23" format.

So how should I encode the tagName for the anchor?

Answer 1

It seems like you're doing two encodes of your URL as c%2523 is the encoded value for c%23. (0x23 = ASCII 35 = #, 0x25 = ASCII 37 = %). As you have two encode calls (Html.Encode and Html.UrlEncode), perhaps removing one of them removes your problem.

Answer 2

# corresponds to the ascii value of 23 in hex. So I guess they use the hex value.

Answer 3

If i recal correctly, then will actionlink automaticly encode the values on the url, so just remove the Html.Encode(tagName), and it should look nicely.

Answer 4

<%= Html.ActionLink(Html.Encode(tagName), 
"tagged" //action,  
"posts" //controller, 
new {tagName=Html.UrlEncode(tagName)} //querystring argument, 
new {@class="tag"} //html attributes) 
%>

Html.ActionLink creates HTML and deals with the escaping issues for you. You should not explicitly Html.Encode the link text, or Html.UrlEncode the parameter.

If a ‘#’ in a parameter value is not being escaped that sounds like a bug in ActionLink() and you might have to generate the link yourself.