Friday, August 26, 2011

How to stop System.Uri un-escaping forward slash characters

Sometimes you want to construct a URI that has an escaped forward slash. For example, the RabbitMQ Management API requires that you encode the default rabbit VirtualHost ‘/’ as ‘%2f’. Here is the URL to get the details of a queue:

http://192.168.1.4:55672/api/queues/%2f/EasyNetQ_Default_Error_Queue

But if I try use WebRequest or WebClient the ‘%2f’ is un-escaped to a ‘/’, so the URL becomes:

http://192.168.1.4:55672/api/queues///EasyNetQ_Default_Error_Queue

And I get a 404 not found back :(

Both WebRequest and WebClient use System.Uri internally. It’s easy to demonstrate this behaviour with the following code:

var uri = new Uri(url);
Console.Out.WriteLine("uri = {0}", uri.PathAndQuery);
// outputs /api/queues///EasyNetQ_Default_Error_Queue

A bit of digging in the System.Uri code thanks to the excellent ReSharper 6.0, and help from this Stack Overflow question, shows that it’s possible to reset some flags and stop this behaviour. Here’s my LeaveDotsAndSlashesEscaped method (it’s .NET 4.0 specific):

private void LeaveDotsAndSlashesEscaped()
{
var getSyntaxMethod =
typeof (UriParser).GetMethod("GetSyntax", BindingFlags.Static | BindingFlags.NonPublic);
if (getSyntaxMethod == null)
{
throw new MissingMethodException("UriParser", "GetSyntax");
}

var uriParser = getSyntaxMethod.Invoke(null, new object[] { "http" });

var setUpdatableFlagsMethod =
uriParser.GetType().GetMethod("SetUpdatableFlags", BindingFlags.Instance | BindingFlags.NonPublic);
if (setUpdatableFlagsMethod == null)
{
throw new MissingMethodException("UriParser", "SetUpdatableFlags");
}

setUpdatableFlagsMethod.Invoke(uriParser, new object[] {0});
}

The usual caveats of poking into system assemblies with reflection apply. Don’t expect this to work with any other version of .NET than 4.0.
 
Now if we re-run our test…
 
LeaveDotsAndSlashesEscaped();
const string url = "http://192.168.1.4:55672/api/queues/%2f/EasyNetQ_Default_Error_Queue";
var uri = new Uri(url);
Console.Out.WriteLine("uri = {0}", uri.PathAndQuery);
// outputs /api/queues/%2f/EasyNetQ_Default_Error_Queue

Voila!
 
If you have a Web.config or App.config file you can also try this configuration setting, which should do the same thing (from this SO question) but I haven’t tried it personally:
 
<uri> 
<schemeSettings>
<add name="http" genericUriParserOptions="DontUnescapePathDotsAndSlashes" />
</schemeSettings>
</uri>

4 comments:

SAAD said...

thanks man !!!

Stif said...

Thanks, this post did not solve my problem but it put me in the right direction. See my post on stackoverlfow: http://stackoverflow.com/questions/16170442/wcf-uritemplate-urlencode

Anonymous said...

Wow... that's so dangerous and so hacky.

Henry Motu said...

I've been working on this bug for 2 days.
Thanks. You've made my day!