ForceCanonicalPathAndQuery_mono.cs

using System;
using System.Net;
using System.Reflection;

namespace UriTest
{
  //a mono version of the ForceCanonicalPathAndQuery code here: http://stackoverflow.com/questions/781205/getting-a-url-with-an-url-encoded-slash
  class Program
  {
    static void Main(string[] args)
    {
      var uri = new Uri("http://www.yahoo.com/%2F?Foo=Bar%2F#frag");
      UriHelper.ForceCanonicalPathAndQuery(uri);
      Console.WriteLine ("uri.ToString() - " + uri.ToString ());
      Console.WriteLine ("uri.AbsoluteUri - " + uri.AbsoluteUri);
      Console.WriteLine ("uri.Host - " + uri.Host);
      Console.WriteLine ("uri.Query - " + uri.Query);
      Console.WriteLine ("uri.PathAndQuery - " + uri.PathAndQuery);
      Console.WriteLine ("uri.AbsolutePath - " + uri.AbsolutePath);
      Console.WriteLine ("uri.Fragment - " + uri.Fragment);
    }

    public class UriHelper {
      private static Type uriType = typeof(Uri);
      private static FieldInfo sourceField;
      private static FieldInfo queryField;
      private static FieldInfo pathField;
      private static FieldInfo cachedToStringField;
      private static FieldInfo cachedAbsoluteUriField;

      static UriHelper ()
      {
        sourceField = uriType.GetField ("source", BindingFlags.NonPublic | BindingFlags.Instance);
        queryField = uriType.GetField ("query", BindingFlags.NonPublic | BindingFlags.Instance);
        pathField = uriType.GetField ("path", BindingFlags.NonPublic | BindingFlags.Instance);
        cachedToStringField = uriType.GetField ("cachedToString", BindingFlags.NonPublic | BindingFlags.Instance);
        cachedAbsoluteUriField = uriType.GetField ("cachedAbsoluteUri", BindingFlags.NonPublic | BindingFlags.Instance);
      }

      public static void ForceCanonicalPathAndQuery(Uri uri)
      {
        var source = (string) sourceField.GetValue (uri);
        cachedToStringField.SetValue (uri, source);
        cachedAbsoluteUriField.SetValue (uri, source);
        var fragPos = source.IndexOf ("#");
        var queryPos = source.IndexOf ("?");
        var start = source.IndexOf (uri.Host) + uri.Host.Length;
        var pathEnd = queryPos == -1 ? fragPos : queryPos;
        if (pathEnd == -1)
          pathEnd = source.Length+1;
        var path = queryPos > -1 ? source.Substring (start, pathEnd - start) : source.Substring (start);
        pathField.SetValue (uri, path);
        queryField.SetValue(uri, fragPos > -1 ? source.Substring(queryPos, fragPos - queryPos) : source.Substring(queryPos));
      }
    }
  }
}

/* 

outputs:

uri.ToString() - http://www.yahoo.com/%2F?Foo=Bar%2F#frag
uri.AbsoluteUri - http://www.yahoo.com/%2F?Foo=Bar%2F#frag
uri.Host - www.yahoo.com
uri.Query - ?Foo=Bar%2F
uri.PathAndQuery - /%2F?Foo=Bar%2F
uri.AbsolutePath - /%2F
uri.Fragment - #frag

*/