Abort reading from stream when request has been aborted

[retroplasma]

Hi,

First of all, thanks for the wonderful project! There is a thing that I couldn't figure out yet:

I implemented an IFileSystem, IDocument and so forth. When GETting large files I noticed that if the request is aborted by the client, the server keeps reading data using OpenReadAsync from my subclass of Stream (the read method keeps being called). The cancellationToken doesn't seem to be triggered. Can we access HttpContext.RequestAborted somehow? Or is there another preferred way to react to client-side cancellation of a request?

I tested it by cURLing the server (curl http://localhost:5809/_dav/file.dat) and aborting using CTRL+C.

Thanks!

[fubar-coder]

That's a tough question. I'd check if this is a problem with the stream or if the cancellation token isn't triggered

[retroplasma]

@fubar-coder I put logs in the Stream's ReadAsync and Read function and checked the cancellation token from ReadAsync as well as the one from OpenReadAsync. The tokens are not triggered when the request is cancelled by the client.

Maybe this line is the cause?https://github.com/FubarDevelopment/WebDavServer/blob/master/src/FubarDev.WebDavServer/Handlers/Impl/GetResults/WebDavFullDocumentResult.cs#L73
(await content.CopyToAsync(response.Body).ConfigureAwait(false);)

Here's how I tested it:

Code

CustomFile.cs

public Task<Stream> OpenReadAsync(CancellationToken cancellationToken)
{
	Console.WriteLine(cancellationToken.IsCancellationRequested ? "wants to be cancelled" : "-");
	return Task.FromResult<Stream>(new CustomStream(/* ... */, cancellationToken));
}

CustomStream.cs

public override async Task<int> ReadAsync(byte[] buffer, int _offset, int count, CancellationToken cancellationToken)
{
	Console.WriteLine(cancellationToken.IsCancellationRequested ? "wants to be cancelled" : "-");
	Console.WriteLine(this.cancellationToken.IsCancellationRequested ? "wants to be cancelled" : "-");
	// ...
}

All three logs keep printing "-" after request cancellation.

Edit: Related CoreFX PR?

[fubar-coder]

Good catch! I will fix this.

[retroplasma]

@fubar-coder i ran the new code; unfortunately cancellation is still not triggered for me if the client cancels the request.

[fubar-coder]

Hmm, ok, will try again. I'm currently fighting the build server 😢

[retroplasma]

Thanks for doing this! I'm looking around as well and just found this IIS issue, but I'm only using Kestrel and they fixed something like this here. I'm new to ASP though and not 100% sure if that's related.

[retroplasma]

Nice! I'll try it
edit: Awesome! Thanks a lot!