Make `H2Upgraded` public to allow downcasting `Upgraded` for `Sync` access to underlying IO

[imlk0]

Hi, I'd like to request that hyper::proto::h2::H2Upgraded<T> be made pub, so users can downcast an hyper::upgrade::Upgraded object to access the underlying I/O type for HTTP/2 connections.

Problem

Currently, Upgraded is not Sync, which prevents sending it across threads or storing it in Sync contexts. While HTTP/1 upgraded connections can be downcast using .downcast::<Tokio<TcpStream >>(), but the underlying I/O type for HTTP/2 H2Upgraded<T> is private, making it impossible to downcast and recover the inner IO (which is often Sync).

// This fails to compile — `H2Upgraded` is private
upgraded.downcast::<hyper::proto::h2::H2Upgraded<bytes::Bytes>>()

Note

• The construction of H2Upgraded:
  • client side:

    hyper/src/proto/h2/client.rs

    Lines 591 to 593 in be18a92

    	let (h2_up, up_task) = super::upgrade::pair(send_stream, recv_stream, ping);
    	self.exec.execute_upgrade(up_task);
    	let upgraded = Upgraded::new(h2_up, Bytes::new());

  • server side:

    hyper/src/proto/h2/server.rs

    Lines 495 to 503 in be18a92

    	let (h2_up, up_task) = super::upgrade::pair(
    	send_stream,
    	connect_parts.recv_stream,
    	connect_parts.ping,
    	);
    	connect_parts
    	.pending
    	.fulfill(Upgraded::new(h2_up, Bytes::new()));
    	self.exec.execute_upgrade(up_task);

• This issue is partly similar to hyper-util auto version detection breaks the ability to use Upgraded::downcast #3587, but it doesn't solve the problem in the HTTP/2 scenario.

Thanks for all the great work on Hyper! I'd be happy to help implement this if you agree.

[seanmonstar]

I don't think I'd necessarily want to make H2Upgraded public.

But Upgraded is Send, so you can send it to another thread. By not being Sync, it just means you need to put it in a synchronizing type before you allow thread-safe clones. So Arc<Upgraded> isn't allowed, but Arc<Mutex<Upgraded>> is perfectly legal.