Saving Video Data To File From POST request InputStream in PowerShell - powershell

Question

I am having trouble quite figuring out how to save video data sent to me via a HttpListener in PowerShell. I have the following which I believe is just sending it back to the requester but I'm having trouble just saving it into an MP4 file.
$req = $request
$body = $req.InputStream
$reader = New-Object System.IO.StreamReader ($body, $req.ContentEncoding)
$msg = $reader.ReadToEnd()
$reader.Close()
[byte[]] $buffer = [System.Text.Encoding]::UTF8.GetBytes($msg)
$res.ContentLength64 = $buffer.Length
$res.StatusCode = 200
$res.OutputStream.Write($buffer, 0, $buffer.Length)
$res.Close()
Thank you for your time eveyrone!
Update:
I have been able to make files with this, though for some reason in examples they're using 8192 sized byte but PowerShell says it's too big. With this I get zero length files, no errors that I can tell.
$path = "c:\matthew3.mp4"
$file = New-Object System.IO.FileStream $path,CreateNew
[byte]$bytes = 255
[int]$bytes_read = 0
while ( $bytes_read = $request.InputStream.Read($bytes, 0, $bytes.length) > 0 )
{
$file.Write($bytes, 0, $bytes_read)
}
Actually I did get an error:
Exception calling "GetBytes" with "1" argument(s): "Array cannot be null.
Parameter name: chars"
At line:45 char:1
+ $buffer = [System.Text.Encoding]::UTF8.GetBytes($content)
+ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+ CategoryInfo : NotSpecified: (:) [], MethodInvocationException
+ FullyQualifiedErrorId : ArgumentNullException
Exception calling "Write" with "3" argument(s): "Value cannot be null.
Parameter name: buffer"
At line:47 char:1
+ $response.OutputStream.Write($buffer, 0, $buffer.Length)
+ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+ CategoryInfo : NotSpecified: (:) [], MethodInvocationException
+ FullyQualifiedErrorId : ArgumentNullException

Answer 1

So the main developer for our company Nick pointed me in the right direction here.
The main thing is that for the FileStream object I needed to add the Write flag, and use the CopyTo method on the InputStream and then close both of them:
$file = New-Object System.IO.FileStream $path,CreateNew,Write
$context.Request.InputStream.CopyTo($file)
$file.Close()
$context.Request.InputStream.Close()