How to combine URLs with query string parts preserved?

Question

I am writing a C# application that needs to callout to a webapp. I am trying to use System.Uri to combine two URL's: A base URL and the relative path to the specific service (or many) of the webapp I need. I have a class member named webappBackendURL that I want to define in one place, with all calls building from it (webappBackendURL is not defined as close as my examples illustrate).

System.Uri webappBackendURL = new System.Uri("http://example.com/");
System.Uri rpcURL           = new System.Uri(webappBackendURL,"rpc/import");
// Result: http://example.com/rpc/import

This works, however, if webappBackendURL contains a query string, it is not preserved.

System.Uri webappBackendURL = new System.Uri("http://example.com/?authtoken=0x0x0");
System.Uri rpcURL           = new System.Uri(webappBackendURL,"rpc/import");
// Result: http://example.com/rpc/import <-- (query string lost)

Is there a better way combine URLs? The .NET library is extensive, so I'm thinking I might have just overlooked a built-in way to handle this. Ideally, I would like to be able to combine URLs like this:

System.Uri webappBackendURL = new System.Uri("http://example.com/?authtoken=0x0x0");
System.Uri rpcURL           = new System.Uri(webappBackendURL,"rpc/import?method=overwrite&runhooks=true");
// Result: http://example.com/rpc/import?authtoken=0x0x0&method=overwrite&runhooks=true

Answer 1

You could do something like this:

System.Uri webappBackendURL = 
  new System.Uri("http://example.com/?authtoken=0x0x0");
System.Uri rpcURL = new System.Uri(webappBackendURL,
  "rpc/import?ethod=overwrite&runhooks=true" 
  + webappBackendURL.Query.Replace("?", "&"));

Answer 2

Try UriTemplate:

Uri baseUrl = new Uri("http://www.example.com");
UriTemplate template = new UriTemplate("/{path}/?authtoken=0x0x0");
Uri boundUri = template.BindByName(
    baseUrl,
    new NameValueCollection {{"path", "rpc/import"}});

System.UriTemplate has moved around between different versions of .NET. You'll need to determine which assembly reference is correct for your project.