S4005 — "System.Uri" arguments should be used instead of strings

Why is this an issue?

String representations of URIs or URLs are prone to parsing and encoding errors which can lead to vulnerabilities. The System.Uri class is a safe alternative and should be preferred.

This rule raises an issue when a called method has a string parameter with a name containing "uri", "Uri", "urn", "Urn", "url" or "Url" and the declaring type contains a corresponding overload that takes a System.Uri as a parameter.

When there is a choice between two overloads that differ only regarding the representation of a URI, the user should choose the overload that takes a System.Uri argument.

Noncompliant code example

using System;

namespace MyLibrary
{
   public class Foo
   {
      public void FetchResource(string uriString) { }
      public void FetchResource(Uri uri) { }

      public string ReadResource(string uriString, string name, bool isLocal) { }
      public string ReadResource(Uri uri, string name, bool isLocal) { }

      public void Main() {
        FetchResource("http://www.mysite.com"); // Noncompliant
        ReadResource("http://www.mysite.com", "foo-resource", true); // Noncompliant
      }
   }
}

Compliant solution

using System;

namespace MyLibrary
{
   public class Foo
   {
      public void FetchResource(string uriString) { }
      public void FetchResource(Uri uri) { }

      public string ReadResource(string uriString, string name, bool isLocal) { }
      public string ReadResource(Uri uri, string name, bool isLocal) { }

      public void Main() {
        FetchResource(new Uri("http://www.mysite.com"));
        ReadResource(new Uri("http://www.mysite.com"), "foo-resource", true);
      }
   }
}