getting a responseLength for a HttpWebRequest upload from another webfile to stream into the upload when the source doesn't implement ContentLength?

Background - I'm trying to stream an existing webpage to a separate web application, using HttpWebRequest/HttpWebResponse in C#. One issue I'm striking is that I'm trying to set the file upload request content-length using the file download's content-length, HOWEVER the issue seems to be when the source webpage is on a webserver for which the HttpWebResponse doesn't provide a content length.

HttpWebRequest downloadRequest = WebRequest.Create(new Uri("downloaduri")) as HttpWebRequest;
 using (HttpWebResponse downloadResponse = downloadRequest.GetResponse() as HttpWebResponse)
 {
   var uploadRequest = (HttpWebRequest) WebRequest.Create(new Uri("uripath"));
   uploadRequest.Method = "POST";
   uploadRequest.ContentLength = downloadResponse.ContentLength;  // ####

QUESTION: How could I update this approach to cater for this case (when the download response doesn't have a content-length set). Would it be to somehow use a MemoryStream perhaps? Any sample code would be appreciated.

If you're happy to download the response from the other web server completely, that would indeed make life easier. Just repeatedly write into a MemoryStream as you fetch from the first web server, then you know the length to set for the second request and you can write the data in easily (especially as MemoryStream has a WriteTo method to write its contents to another stream).

The downside of this is that you'll take a lot of memory if it's a large file. Is that likely to be a problem in your situation? Alternatives include:

• Writing to a file instead of using a MemoryStream. You'll need to clean up the file afterwards, of course - you're basically using the file system as bigger memory :)
• Using a chunked transfer encoding to "read a chunk, write a chunk"; this may be fiddly to get right - it's certainly not something I've done before.