Idea for handling of async operations for which waiting for the outcome or the outcome itself is irrelevant

[paolobarbolini]

I had an idea. I'm still not sure if it's a good approach the library should promote, but I see sometimes async-nats finds itself in this situation, for example inside Drop implementations or other code in general ^{1 2}.

Here are the assumptions my idea is based on:

1. Sometimes an operation like publishing a Core NATS or a Jetstream message or ACKing a consumer message needs to be done
2. The operation is sometimes handled by doing a tokio::spawn in order not to block the main application loop, ignoring any errors that might occur
3. tokio::spawn can be seen as a sort-of unbounded queue
4. Some async-nats calls can be seen as a fancy wrapper around a bounded mpsc sender
5. It doesn't make sense to have have to go through two queues when the outcome of the first queue is unimportant. Why not then have an API that writes into the internal mpsc sender and ignores the outcome?

This could be implemented via IntoFuture.
Instead of having to duplicate all function calls, let's take publish as an example. The current function signature is:

pub async fn publish(
        &self,
        subject: String,
        payload: Bytes,
    ) -> Result<PublishAckFuture, PublishError>

by changing it into this

pub async fn publish(
        &self,
        subject: String,
        payload: Bytes,
    ) -> PublishBuilder

we could have PublishBuilder implement both IntoFuture and the try_send method, which would be used like so:

// wait for the publish to be sent
jetstream.publish("subject".to_owned(), payload).await;

// try to publish without actually waiting for it to be sent and ignoring any errors
// doesn't work if the `mpsc` channel is full
jetstream.publish("subject".to_owned(), payload).try_send();

The same could be done for a few more methods:

// wait for the ack to be sent
jetstream_message.ack().await;

// don't care about the outcome of sending the ack
// doesn't work if the `mpsc` channel is full
jetstream_message.ack().try_send();

Footnotes

1. https://github.com/nats-io/nats.rs/blob/08342bb3dcde89f0ed02a08f5c040c8f326caa94/async-nats/src/lib.rs#L1020-L1029 ↩

2. https://github.com/nats-io/nats.rs/blob/08342bb3dcde89f0ed02a08f5c040c8f326caa94/async-nats/src/jetstream/consumer/push.rs#L130-L135 ↩