Calling async code with task cancellation triggered by SwiftNIO channel

Related Projects SwiftNIO
1

i have some code that is relying on unstructured tasks to send the right task cancellation signals into some async-colored code.

try await stream.frames.executeThenClose
{
    (
        inbound:NIOAsyncChannelInboundStream<HTTP2Frame.FramePayload>,
        outbound:NIOAsyncChannelOutboundWriter<HTTP2Frame.FramePayload>
    ) in

    let request:Task<ServerResponse, any Error> = .init
    {
        try await self.respond(to: inbound)
    }
    stream.frames.channel.closeFuture.whenComplete
    {
        _ in request.cancel()
    }

    let message:ServerMessage
    do
    {
        message = .init(response: try await request.value)
    }
    catch let error
    {
        message = .init(redacting: error)
    }

    try await outbound.send(message)
}

but since this is relying on unstructured tasks i wondered if there was a better way to achieve this with structured concurrency.

2

Annoyingly we're missing some APIs here that would make this more tractable. In particular, I think we want a nice structured cancelOnClose API, or some way to get us to deliver you a message. Can you file a github issue for this?

3

Given this was something I was just looking into the other week and hit some deadends. I added the issue Add Channel.cancelOnClose(_:) · Issue #2696 · apple/swift-nio · GitHub