FileStream creates an empty file when an error is thrown in CopyToAsync

user_13598555 0
Viewed 195

I am trying to implement a file upload component in my Blazor web application. I am using the approach provided on the Core Blazor InputFile component documentation page.

Here is my code:

await using FileStream fs = new(path, FileMode.Create);
await file.OpenReadStream(MaxFileSize).CopyToAsync(fs);

If OpenReadStream throws an error, (MaxFileSize is exceeded, etc.) the file should not be uploaded. However, since I already created the file stream, an empty file is created at the provided path (an empty text document for example). I am a C# and Blazor newbie so I'm probably just overlooking an easy solution. How can I ensure that an empty file is not uploaded even if an error is thrown?

blazor c#
3 Answers

Well, you can create the file after you've called OpenReadStream:

using var input = file.OpenReadStream(MaxFileSize);
await using FileStream output = new(path, FileMode.Create);
await input.CopyTo(output);

That could still fail leaving an empty or incomplete file of course, because CopyTo could fail, but it at least avoids the problem when OpenReadStream throws an exception.

user_226560

I believe it will be enough to add a file delete action in the catch block.

So your example would look like following:

try 
{ 
    await using FileStream fs = new(path, FileMode.Create);
    await file.OpenReadStream(MaxFileSize).CopyToAsync(fs);
} 
catch (Exception ex) 
{ 
    File.Delete(path); 
    //Re-throw exception 
    throw; 
}
user_36717570

If it's actually throwing an error. Break up the statements and surround with a try catch?

try
{
     var strm = await file.OpenReadStream(MaxFileSize);
     strm.CopyToAsync(fs);
}
catch
{

}

Or check the stream for content before copying in an if statement.

user_84072960
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