Why Does URL-Encoding Slashes in HTTP GET Requests Result in Double Slashes, and How Can This Be Fixed?

Unveiling the Mystery of URL-Encoded Slashes in HTTP GET

In the quest to retrieve data via HTTP GET, developers often encounter the challenge of sending URL-encoded slashes (/). However, a common misconception arises when attempting to transmit this specific character.

As illustrated in the example code, simply including the / in the URL string is insufficient. Instead, the encoded slash is incorrectly interpreted as two slashes, leading to the request being sent as:

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

This behavior violates the OCSP protocol, which mandates transmitting actual / characters instead of '/'.

A Detour into the Unconventional

To address this issue, a workaround has emerged that utilizes a direct modification of the Uri object. By forcibly overriding the PathAndQuery flags, we trick the framework into recognizing our intended URL encoding.

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);
}

While this method is far from ideal, it enables developers to send HTTP GET requests with URL-encoded slashes, satisfying the requirements of specific protocols like OCSP.

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