Detecting file size with MultipartFormDataStreamProvider before file is saved? - file-upload

Question

We are using the MultipartFormDataStreamProviderto save file upload by clients. I have a hard requirement that file size must be greater than 1KB. The easiest thing to do would of course be the save the file to disk and then look at the file unfortunately i can't do it like this. After i save the file to disk i don't have the ability to access it so i need to look at the file before its saved to disk. I've been looking at the properties of the stream provider to try to figure out what the size of the file is but unfortunately i've been unsuccessful.
The test file i'm using is 1025 bytes.
MultipartFormDataStreamProvider.BufferSize is 4096
Headers.ContentDisposition.Size is null
ContentLength is null
Is there a way to determine file size before it's saved to the file system?

Answer 1

Thanks to Guanxi i was able to formulate a solution. I used his code in the link as the basis i just added a little more async/await goodness :). I wanted to add the solution just in case it helps anyone else:
private async Task SaveMultipartStreamToDisk(Guid guid, string fullPath)
{
var user = HttpContext.Current.User.Identity.Name;
var multipartMemoryStreamProvider = await Request.Content.ReadAsMultipartAsync();
foreach (var content in multipartMemoryStreamProvider.Contents)
{
using (content)
{
if (content.Headers.ContentDisposition.FileName != null)
{
var existingFileName = content.Headers.ContentDisposition.FileName.Replace("\"", string.Empty);
Log.Information("Original File name was {OriginalFileName}: {guid} {user}", existingFileName, guid,user);
using (var st = await content.ReadAsStreamAsync())
{
var ext = Path.GetExtension(existingFileName.Replace("\"", string.Empty));
List<string> validExtensions = new List<string>() { ".pdf", ".jpg", ".jpeg", ".png" };
//1024 = 1KB
if (st.Length > 1024 && validExtensions.Contains(ext, StringComparer.OrdinalIgnoreCase))
{
var newFileName = guid + ext;
using (var fs = new FileStream(Path.Combine(fullPath, newFileName), FileMode.Create))
{
await st.CopyToAsync(fs);
Log.Information("Completed writing {file}: {guid} {user}", Path.Combine(fullPath, newFileName), guid, HttpContext.Current.User.Identity.Name);
}
}
else
{
if (st.Length < 1025)
{
Log.Warning("File of length {FileLength} bytes was attempted to be uploaded: {guid} {user}",st.Length,guid,user);
}
else
{
Log.Warning("A file of type {FileType} was attempted to be uploaded: {guid} {user}", ext, guid,user);
}
var responseMessage = new HttpResponseMessage(HttpStatusCode.BadRequest)
{
Content =
st.Length < 1025
? new StringContent(
$"file of length {st.Length} does not meet our minumim file size requirements")
: new StringContent($"a file extension of {ext} is not an acceptable type")
};
throw new HttpResponseException(responseMessage);
}
}
}
}
}

Answer 2

You can also read the request contents without using MultipartFormDataStreamProvider. In that case all of the request contents (including files) would be in memory. I have given an example of how to do that at this link.
In this case you can read header for file size or read stream and check the file size. If it satisfy your criteria then only write it to desire location.