Examples on `hyper::client::connect` do not compile

[davidbarsky]

I'm trying to replicate the example with service_fn in https://docs.rs/hyper/0.13.3/hyper/client/connect/index.html, but I'm unable to get this example to compile:

let connector = service_fn(|_: http::Uri| async {
    tokio::net::TcpStream::connect("127.0.0.1:1337")
});
let mut client = hyper::Client::builder().build(connector);

Here's a minimal reproduction: https://play.rust-lang.org/?version=stable&mode=debug&edition=2018&gist=2a85ed2fb9b1025826e81243f72c9fc0.

[davidbarsky]

The non-service_fn-using example does compile:

https://play.rust-lang.org/?version=stable&mode=debug&edition=2018&gist=8289d6452f98e76d5f54790079ca9456

[LucioFranco]

@davidbarsky if you drop the async block it should compile.

[seanmonstar]

I tried to fix this by removing the async keyword, and then realized that TcpStream::connect is an !Unpin future, and Unpin is currently required. Removing that requirement is tricky, since connecting actually selects on a connect future and a pool checkout, and if the connect loses, its spawned in the background to eventually get added to the pool.

It could be changed to be service_fn(|_| Box::pin(TcpStream::connect(host))), if that's not too ugly...