Async Connection Trait

[pv42]

With #255 support for tokio-based async was merged, adding async versions of write_versioned_msg and read_v2_msg which is very welcome (as it is something I was thinking of doing myself).

I suggest adding an async version of the connection trait similar to MavConnection<M: Message>:

#[async_trait]
pub trait AsyncMavConnection<M: Message> {
    async fn recv(..) -> ..
    async fn send(..) -> ..
    fn set_protocol_version(..)
    fn get_protocol_version(..) -> ..
    async fn send_frame(..) -> ..
    async fn recv_frame(..) -> .. 
    async fn send_default(..) -> ..
}

And then implementing it for the tcp, udp, file and potentially serial (unsure if/how tokio support that) connections and providing a public function to open async connections:
pub async fn connect_async<M: Message>(address: &str) -> io::Result<Box<dyn AsyncMavConnection<M> + Sync + Send>>

If this is something that would fit and if @joaoantoniocardoso is not already working on it I would be happy to submit a PR.

[joaoantoniocardoso]

Hi @pv42, nice idea, surely mavlink-camera-manager (and potentially mavlink2rest) would benefit from that!

To contextualize, I did implement these tokio-based async read/write because I've been experimenting with a new mavlink router written in rust (mavlink-server). This router can also be refactored to make use of that, but it already has an implementation (which might help us here?).

Feel free to use any of that code if useful, the mavlink-server repo still lacks a license file, but it's intended to be MIT (edit: MIT License file added).

[BWStearns]

I was literally looking to see if this existed last night! +100!

[joaoantoniocardoso]

@pv42 just so you know, I'm reworking the tokio async reader around tokio-utils' codec, so we can ensure a frame would be received from the raw read functions, and using the same codec you can have a tokio's UdpStream.