Add isahc metrics to response if available

[asaaki]

Those metrics then can be consumed via the response extensions.
They contain very intersesting request timing data, useful for stats, tracing, benchmarks and similar use cases.

let res: http_types::Response = some_req.await?;
if let Some(metrics) = &res.ext::<isahc::Metrics>() {
  // use the metrics ...
}

[Fishrock123]

Don't these need to be manually enabled?

[Fishrock123]

We probably don't want them on all the time, so this should either have some kind of api or a configuration flag if this crate is going to be turning them on.

Or are these available if you http_client::isahc::IsahcClient::from_client()?

[asaaki]

The metrics have to be manually enabled when building the client, so they are not always populated.
That's why it uses the let binding, because .metrics() returns an option based on the enablement of this feature.

An example how to create a surf client with isahc's metrics enabled:
https://github.com/asaaki/opentelemetry-surf/blob/d23ea22991c92abab8ce0b24c6d1f0f2c13c1689/examples/metrics.rs#L34-L45

So yes, only via http_client::isahc::IsahcClient::from_client() works. The default client would not have metrics at all.

[asaaki]

Hi there,
is anything blocking the merge?
Can I do something to unblock it?

[Fishrock123]

Note: a new release is kinda blocked on figuring out http-rs/surf#271 atm.