How Can I Prevent URL Encoding from Modifying a Percent-Encoded Slash in a GET Request?

Overcoming Slash URL-Encoding Dilemma during GET Requests

In an attempt to send an HTTP GET request to a URL containing a percent-encoded slash (/), such as "http://example.com//," a common approach is to utilize the WebClient class as follows:

using (WebClient webClient = new WebClient())
{
  webClient.DownloadData("http://example.com/%2F");
}

However, this method results in an unexpected outcome. The slash character gets transformed into an extra slash during transmission, leading to the following request being sent:

GET // HTTP/1.1
Host: example.com
Connection: Keep-Alive

This issue arises when using OCSP over HTTP/GET, which requires transmitting an actual / instead of '/' to ensure protocol compliance.

A Potential Solution

Although not ideal, the following code snippet presents a workaround for the issue:

Uri uri = new Uri("http://example.com/%2F");
ForceCanonicalPathAndQuery(uri);
using (WebClient webClient = new WebClient())
{
  webClient.DownloadData(uri);
}

void ForceCanonicalPathAndQuery(Uri uri){
  string paq = uri.PathAndQuery; // need to access PathAndQuery
  FieldInfo flagsFieldInfo = typeof(Uri).GetField("m_Flags", BindingFlags.Instance | BindingFlags.NonPublic);
  ulong flags = (ulong) flagsFieldInfo.GetValue(uri);
  flags &= ~((ulong) 0x30); // Flags.PathNotCanonical|Flags.QueryNotCanonical
  flagsFieldInfo.SetValue(uri, flags);
}

This workaround involves modifying the Uri object's internal flags to force CanonicalPathAndQuery, ensuring that the slash character is preserved during transmission.

Disclaimer

It's important to note that this approach is not guaranteed to be compatible with future versions of the framework. Always proceed with caution when modifying internal class behavior.

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