How to encode a path that contains a hash?

Question

How do you properly encode a path that includes a hash (#) in it? Note the hash is not the fragment (bookmark?) indicator but part of the path name.

For example, if there is a path like this:

http://www.contoso.com/code/c#/somecode.cs

It causes problems when you for example try do this:

Uri myUri = new Uri("http://www.contoso.com/code/c#/somecode.cs");

It would seem that it interprets the hash as the fragment indicator.

It feels wrong to manually replace # with %23. Are there other characters that should be replaced? There are some escaping methods in Uri and HttpUtility but none seem to do the trick.

Answer 1

There are a few characters you are not supposed to use. You can try to work your way through this very dry documentation, or refer to this handy URL summary on Stack Overflow.

If you check out this very website, you'll see that their C# questions are encoded %23.

Stack Overflow C# Questions

You can do this using either (for ASP.NET):

string.Format("http://www.contoso.com/code/{0}/somecode.cs", 
    Server.UrlEncode("c#")
);

Or for class libraries / desktop:

string.Format("http://www.contoso.com/code/{0}/somecode.cs",
    HttpUtility.UrlEncode("c#")
);

Answer 2

Did some more digging friends and found a duplicate question for Java: HTTP URL Address Encoding in Java

However, the .Net Uri class does not offer the constructor we need, but the UriBuilder does.

So, in order to construct a proper URI where the path contains illegal characters, do this:

// Build Uri by explicitly specifying the constituent parts. This way, the hash is not confused with fragment identifier
UriBuilder uriBuilder = new UriBuilder("http", "www.contoso.com", 80, "/code/c#/somecode.cs");

Debug.WriteLine(uriBuilder.Uri);
// This outputs: http://www.contoso.com/code/c%23/somecode.cs

Notice how it does not unnecessarily escape parts of the URI that does not need escaping (like the :// part) which is the case with HttpUtility.UrlEncode. It would seem that the purpose of this class is actually to encode the querystring/fragment part of the URL - not the scheme or hostname.