Async streaming of request body and response

[paulyoung]

Until recently, I was interacting with a canister via the HTTP interface using a reqwest client.

That all worked fine but I wanted a better story around authentication so I started migrating to ic-agent.

I'm almost done with that but ran into something at the very last step that is making me reconsider my approach to using ic-agent (not whether to use ic-agent at all, just my approach to using it)

My previous code relies on the fact that reqwest::blocking::Body::new takes a reader (R: Read + Send + 'static), and that I can configure a request by providing a reference to a reader that will get written to later.

For now I needed things to work in a blocking context, and it was easier to use the reqwest::blocking variant of things so I did that. I had planned to investigate switching to the async version at some point where the equivalent method appears to be reqwest::Body::wrap_stream

Since I at least know that the blocking version of reqwest allows providing a reader, and ic-agent also uses reqwest in ReqwestHttpReplicaV2Transport, I'm wondering if ic-agent could expose a similar interface.

Could agent::QueryBuilder::with_arg and agent::UpdateBuilder::with_arg be generalized to take readers instead?

If that isn't feasible, is there another approach that would enable async streaming of the request body and response?

[domwoe]

@adamspofford-dfinity Any thoughts?