Call to http.DetectContentType has trailing NUL bytes in buffer

[Michael Crawford]

In writeMultipartFormFile, the call to http.DetectContentType is passed a buffer with potentially trailing 0 bytes. As a result, text/plain is never detected in such cases.

cbuf should be trimmed to size to ensure text/plain is property detected:

// Auto detect actual multipart content type
cbuf := make([]byte, 512)
size, err := r.Read(cbuf)
if err != nil && err != io.EOF {
  return err
}

partWriter, err := w.CreatePart(createMultipartHeader(fieldName, fileName, http.DetectContentType(cbuf[:size])))
if err != nil {
  return err
}