Missing null check for boundary

[JornWildt]

In OpenRasta/IO/BoundaryStreamReader.cs we have:

public BoundaryStreamReader(string boundary, Stream baseStream, Encoding streamEncoding, int bufferLength)
{
  if (baseStream == null)
    throw new ArgumentNullException("baseStream");
  if (!baseStream.CanSeek || !baseStream.CanRead)
    throw new ArgumentException("baseStream must be a seekable readable stream.");
  if (bufferLength < boundary.Length + 6)
    throw new ArgumentOutOfRangeException(nameof(bufferLength),
      "The buffer needs to be big enough to contain the boundary and control characters (6 bytes)");

Unfortunately, if you screw up your request and forget the boundary element in the content-type header, you can have boundary = null in which case if (bufferLength < boundary.Length + 6) fails with a null reference, making it difficult to know what happend.

In my case someone decided to send this equest:

POST ...
Content-Type: multipart/form-data
... other headers ...
boundary: 125a17bf-935d-4686-b0c9-95a9543bf255
Content-Length: ...

[serialseb]

Interesting. Boundary is required so in case it's invalid we should send back a 400 indeed, especially as it's a required element. For reference, rfc is at https://tools.ietf.org/html/rfc7578