How do I convert an async / standard library future to futures 0.1?

Question

I want to use the async function to parse the inbound stream progressively, but actix-web requires impl Future

Answer 1

std::future -> future@0.1 conversion steps:

• The future needs to be TryFuture (Output = Result<T, E>)
• The future needs to be Unpin (you can use boxed combinator)
• Finally, you can call the compat combinator

Your inbound function:

fn inbound(
    req: HttpRequest,
    stream: web::Payload,
) -> impl Future<Item = HttpResponse, Error = Error> {
    let fut = async_inbound(&req, &stream);
    fut.unit_error().boxed_local().compat()
}

The inbound function signature is fine, but the conversion isn't.

The async_inbound function isn't TryFuture (because of -> HttpResponse). You're trying to convert it with the unit_error combinator, but the result is Result<HttpResponse, ()> and you want Result<HttpResponse, Error>. Fixed inbound function:

fn inbound(
    req: HttpRequest,
    stream: web::Payload,
) -> impl Future<Item = HttpResponse, Error = Error> {
    let fut = async_inbound(req, stream);
    fut.boxed_local().compat()
}

Your async_inbound function:

async fn async_inbound(req: &HttpRequest, stream: &web::Payload) -> HttpResponse {
    // ...
}

The first issue here is to replace -> HttpResponse with -> Result<HttpResponse>. Another problem is that you're passing reg and stream by reference. Move them as there's no need to take a reference and you'll need 'static. Fixed async_inbound function:

async fn async_inbound(req: HttpRequest, stream: web::Payload) -> Result<HttpResponse> {
    let mut compat_stream = stream.compat();

    while let Some(data) = compat_stream.try_next().await? {
        println!("{:?}", data);
    }

    Ok(HttpResponse::Ok().content_type("text/html").body("RESP"))
}