tokio-tungstenite | Lightweight stream | Websocket library

The concept I was missing was that of blanket implementations where traits in modules that know nothing about the code in my module can add functionality to my structs. This is so long as the trait bounds of the external code fit my code.

In this situation WebSocketStream implements Stream. There is a trait StreamExt in the futures crate that knows nothing about WebSocketStream but is a blanket implementation for Stream. It provides the functionality of split() to Stream and as WebSocketStream implements Stream it also gets that functionality.

Hyper is using Tokio version 0.2.x, while tokio-tungstenite is using Tokio version 0.3.x. The changelog from Tokio 0.2 to 0.3 included breaking changes to the AsyncRead and AsyncWrite traits, making the two incompatible with their version 0.2 counterparts.

You can use the tokio_compat_02 crate to bridge the two until Hyper release a new version (also upgrade your own tokio version to 0.3 in Cargo.toml), alternatively downgrade tokio-tungstenite to 0.11.0 which uses tokio 0.2.x if you prefer.

The documentation on docs.rs is incorrect. If you build the docs locally, you'll see the correct signature of connect_async:

FnMut is an anonymous struct, since FnMutcaptured the &mut outgoing, it becomes a field inside of this anonymous struct and this field will be used on each call of FnMut , it can be called multiple times. If you lose it somehow (by returning or moving into another scope etc...) your program will not able to use that field for further calls, due to safety Rust Compiler doesn't let you do this(for your both case).

In your case instead of capturing the &mut outgoing we can use it as argument for each call, with this we'll keep the ownership of outgoing. You can do this by using fold from futures-rs: