Go http + context

http_context.go

// While the Go documentation promotes the context package for keeping track of request context and cancelation, to
// actually use it for canceling work in http requests some plumbing is necessary:

// getCancelableContextFromResponseWriter gets a context.Context that is canceled when the client (browser) closes the connection
func getCancelableContextFromResponseWriter(w http.ResponseWriter) context.Context {

	// Create a context that can be handed down to the workers to relay cancellation
	ctx, cancelContext := context.WithCancel(context.Background())

	// Get a channel that receives a value when the request is canceled
	cn := w.(http.CloseNotifier)
	cc := cn.CloseNotify()

	// Connect the channel to the cancel function
	go func() {
		<-cc
		cancelContext()
	}()

	return ctx
}

// contextIsCanceled returns true if the Context ctx is canceled
func contextIsCanceled(ctx context.Context) bool {
	select {
	case <-ctx.Done():
		// There is never anything written to the channel, but when the channel is closed, this case will also be
		// chosen, so if we are here the channel must have been closed
		return true
	default:
		return false
	}
}