How to Convert from MemoryStream to FileStream to pass to MS Graph?

Question

I have a MemoryStream object that contains the contents of a file. I would like to convert it from a MemoryStream to a FileStream in order to pass it to MS Graph's LargeFileUploadTask () method.

It seems that the method accepts the generic type called "Stream" so I tried using it as is, but it's taking a very long time. In fact I get an HTTP timeout for larger streams.

I have another method similar to this one that also uses the LargeFileUploadTask and trying to upload the same file works - it's using a FileStream (the difference between the two methods is that one writes to a local file, and then opens a filestream before sending to MS Graph, and the one here receives a memorystream as a parameter)

Code

  private static async Task<Boolean> UploadInChunksToSharepoint(MemoryStream fileContents, string fileName)

 ....

 // Max slice size must be a multiple of 320 KiB
 int maxSliceSize = 320 * 204800 * 4;
 var fileUploadTask =
 new LargeFileUploadTask<DriveItem>(uploadSession, fileContents, maxSliceSize);

What I've Tried

In reading other posts, I see that there's a WriteTo method in the fileContents object. So i tried something like this:

 FileStream fileStream = new FileStream();
 fileContents.WriteTo(fileStream);

But... I guess I can't do that because the FileStream doesn't allow you to just initialize without any parameters. If there's a way... I'd like to be able to try this to compare apples to apples between the two methods to see why there's such a time diff.

In the meantime, I'm poking around the rest of the code to see if there might be other deltas that I just missed.

Answer 1

I have a MemoryStream object that contains the contents of a file. I would like to convert it from a MemoryStream to a FileStream in order to pass it to MS Graph's LargeFileUploadTask() method

But the docs you linked simply state that a Stream is required:

Yes, a FileStream is a Stream but a MemoryStream is also a Stream and is a "readable, seekable stream" like the docs say is required; it means you can just pass the MemoryStream you have for the uploadStream parameter.

Perhaps make sure you've Seek 'd it to Position 0 before you pass it.. If you've just finished writing into a Memorystream, it's Position ed at the end. If you then pass it to something that will start reading from it, that thing usually reads nothing (because the stream is at the end) - seek the stream back to the start/where you want the upload to begin because you should assume that the thing you give it to will not seek it before reading from it

Answer 2

The OP said the problem was that they forgot to rewind the MemoryStream before attempting to use it as the source of a HTTP request payload.

@Dai, that's all it was. I reset position to 0. if you want to add as answer... i'll accept

Gladly.

---

So watch out if you have this:

using( MemoryStream ms = new MemoryStream() )
{
    using( StreamWriter wtr = new StreamWriter( ms, false ) )
    {
        CopyLoremIpsum( wtr );
    }
    
    await UploadStreamAsync( ms );
}

The StreamWriter (or any other writing action) will set the MemoryStream.Position to the end of the stream, where it cannot be read any further (basically as if you had a cassette tape movie or VHS played past the end-credits).

So make sure you reset .Position or use .Seek after writing to it, but before attempting to read from it:

using( MemoryStream ms = new MemoryStream() )
{
    using( StreamWriter wtr = new StreamWriter( ms, false ) )
    {
        CopyLoremIpsum( wtr );
    }

    ms.Position = 0;
    
    await UploadStreamAsync( ms );
}