Changes the return value of Connection::into_parts in the server upgrade API #1471
Description
In the upgrade API provided by the current master, the fields of Parts<T> returned from into_parts() are only the underling I/O and buffer. In order to pass the context genereted within the Service::call to the task of lower layer, it is necessary to use the message passing using the channel as follows:
// A pair of mpsc channel to pass a value of context.
let (tx, rx) = futures::sync::mpsc::unbounded();
let service = service_fn(move |req| {
...
// send the value of context to the following connection task
if some_condition(req) {
tx.unbounded_send(context);
}
Ok(response)
});
let conn = protocol.serve_connection(io, service);
// task to manage a TCP connection considering upgrade
let mut conn_opt = Some(conn);
let mut rx_opt = Some(rx);
let task = poll_fn(move || {
try_ready!(conn_opt.as_mut().unwrap().poll_without_shutdown());
let conn = conn.take().unwrap();
let Parts { io, read_buf, .. } = conn.into_parts();
// Try to retrieve the value of the context.
let mut rx = rx_opt.take().unwrap();
match rx.poll().unwrap() {
Ok(Async::Ready(Some(context))) => {
// migration to upgraded protocol
},
_ => {
// shutdown I/O
}
}
});Using such a method complicates the connection between the Service layer and the lower connection task. To avoid this, the modification of the upgrade API by adding additional field to the return value from Connection::into_parts() is required.
My suggestion is to add the value of Service used in HTTP as follows:
#[derive(Default)]
struct MyService {
// such internal mutability will become unnecessary
// by changing the receiver of Service::call to &mut self.
context: RefCell<Option<UpgradeContext>>,
}
impl Service for MyService {
fn call(&self, req: Request) -> Self::Future {
// set the value of context
if some_condition(req) {
*context.borrow_mut() = Some(context);
}
Ok(response)
}
}
let conn = protocol.serve_connection(io, MyService::default());
let mut conn_opt = Some(conn);
let task = poll_fn(move || {
try_ready!(conn_opt.as_mut().unwrap().poll_without_shutdown());
// There is no additional channel to receive the value of context.
let conn = conn.take().unwrap();
let Parts { io, read_buf, service, .. } = conn.into_parts();
match service.context {
Some(context) => {
// migration to upgraded protocol
},
_ => {
// shutdown I/O
}
}
});Is it possible to make such changes?