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1914ea7076
As relict from very early designs of `connlib`, the `Callbacks` trait is still present and defines how the host app receives events from a running `Session`. Callbacks are not a great design pattern however because they force the running code, i.e. `connlib`s event-loop to execute unknown code. For example, if that code panics, all of `connlib` is taken down. Additionally, not all consumers may want to receive events via callbacks. The GUI and headless client for example already have their own event-loop in which they process all kinds of things. Having to deal with the `Callbacks` interface introduces an odd indirection here. To fix this, we instead return an `EventStream` when constructing a `Session`. This essentially aligns the API of `Session` with that of a channel. You receive two handles, one for sending in commands and one for receiving events. A `Session` will automatically spawn itself onto the given runtime so progress is made even if one does not poll on these channel handles. This greatly simplifies the code: - We get to delete the `Callbacks` interface. - We can delete the threaded callback adapter. This was only necessary because we didn't want to block `connlib` with the handling of the event. By using a channel for events, this is automatically guaranteed. - The GUI and headless client can directly integrate the event handling in their event-loop, without having to create an indirection with a channel. - It is now clear that only the Apple and Android FFI layers actually use callbacks to communicate these events. - We net-delete 100 LoC