fix(examples): Fix tower examples

[smhmayboudi]

based on [tower issue 547] (tower-rs/tower#547), "The original service is ready, but the clone is not necessarily ready."

Issue Number: #545

[LucioFranco]

Im not totally sure how this fixes that bug?, because once you produce the future you can call call at any time from that cloned service.

[LucioFranco]

We actually want to keep it this way because it shows how you can embed async work around the future of the channel.

[smhmayboudi]

There is another solution which we can apply.

let clone = self.inner.clone();
let mut inner = std::mem::replace(&mut self.inner, clone);
Box::pin(async move {
    // Do extra async work here...
    channel.call(req).await.map_err(Into::into)
})

[olix0r]

@LucioFranco See my comment here tower-rs/tower#547 (comment)

[LucioFranco]

Oh interesting.....maybe the mem replace works? @olix0r what do you think?

[smhmayboudi]

Everything is fine?

[smhmayboudi]

The solution is working in my project and your example. The clone is acting properly on the server-side, but not on client-side. It seems the clone needs more time to be ready or somehow have to call pull_ready again.

[moh-abk]

Any update on this @smhmayboudi ?

[smhmayboudi]

@LucioFranco Did you reach any conclusion?

[LucioFranco]

@davidpdrsn since you've been working a lot on tower recently any thoughts on this?

[davidpdrsn]

Suggested change

	// Do async work here....
	Box::pin(async move {
	// Do async work here....
	svc.call(req).await
	})
	Box::pin(self.inner.call(req).err_into::<Self::Error>())
	let clone = self.inner.clone();
	let mut inner = std::mem::replace(&mut self.inner, clone);
	Box::pin(async move {
	// Do extra async work here...
	inner.call(req).await.map_err::<Self::Error>()
	})

[davidpdrsn]

Suggested change

	// Do extra async work here...
	Box::pin(async move {
	// Do extra async work here...
	channel.call(req).await.map_err(Into::into)
	})
	Box::pin(self.inner.call(req).err_into::<Self::Error>())
	let clone = self.inner.clone();
	let mut inner = std::mem::replace(&mut self.inner, clone);
	Box::pin(async move {
	// Do extra async work here...
	inner.call(req).await.map_err::<Self::Error>()
	})

This was we still make it clear to users where to add additional async code.

[davidpdrsn]

I agree with @olix0r. This fix is correct. However as mentioned I think we should use an explicit async block to make it clear to users who to add additional async. I submitted two suggestions.

[davidpdrsn]

Superseded by #624