Hello,

I'm trying to add image previewing to our .Net 6.0.8 Blazor Wasm app using the Telerik Blazor UI FileSelect component. I'd like to be able to create a local url for previewing and also hold onto the file's contents for saving later. There currently doesn't seem to be any great examples/references for doing this using the Telerik FileSelect locally. So, I started looking at the official MS Blazor documentation around images, file uploads and downloads - the most relevant content seemed to be around giving a file's stream to a DotNetStreamReference, then handing it off to JS interop to create a URL from a Blob.

It was already quite slow when testing with a 4KB~ image, but became absolutely unusable once testing things with a larger 4MB~ image. To rule out the Telerik FileSelect's involvement I started testing with the native Blazor FileInput component. I noticed that the sending the DotNetStreamReference to JS interop took a long time itself and learned that .Net 6 added the ability to pass a byte[] almost instantly to JS interop. I was then able to see image previews quickly using the native FileInput component while hosting a file from a byte[]. With this new knowledge in hand I attempted to migrate this new workflow over to the Blazor FileSelect component, but unfortunately there doesn't seem to be a faster way to get a byte[] from the FileSelectFileInfo's Stream.

I'm seeing similar performance issues between the native FileInput using a stream and the Telerik FileSelect using a stream or byte[]. These are both taking around 4-5 minutes to host a file with a locally generated url and preview the image. In contrast I'm seeing wait times around 3-12 seconds using the native FileInput/IBrowserFile, this

byte[] iBrowserFileBytes = new byte[iBrowserFile.Size];
await iBrowserFile.OpenReadStream(maxFileSize).ReadAsync(iBrowserFileBytes);

Please see the attached Blazor Wasm code to recreate the issue. I've included 6 file inputs to test out the difference in performance between each scenario, but the most important file input is the "Blazor InputFile - HostFromByteArray" which shows the most promise. Attached is also the larger file that I was testing against. This might be a bug or maybe I'm just not reading from the FileSelectFileInfo's Stream in the most efficient way.

The only relevant code not attached is likely just this one from Program.cs:

// ...
builder.Services.AddSingleton<IJSInProcessRuntime>(services => (IJSInProcessRuntime)services.GetRequiredService<IJSRuntime>());
// ...