Wasmtime: block on async and reqwest

[radu-matei]

Linker-defined functions cannot be asynchronous yet (see bytecodealliance/wasmtime#2434).

This means the actual host call that performs the HTTP request must at some point block - and depending on how the runtime was started, it is possible for it to just hang right now, and the current implementation is put together without any thought into how other runtimes might need to use this.

wasi-experimental-http/crates/wasi-experimental-http-wasmtime/src/lib.rs

Lines 86 to 92 in a94a758

	let res = match block_on(
	client
	.request(method, &url)
	.headers(headers)
	.body(req_body)
	.send(),
	) {

cc @thomastaylor312

[thomastaylor312]

@radu-matei I’d use the blocking reqwest client for now. However at least for Tokio you can tell if you are on a runtime with Handle::try_current() and then spawning on the runtime handle if it exists

[radu-matei]

After some more testing with WAGI, it turns out that blocking on the current executor could end up deadlocking.
Spawning a new one could fix it.

Reopening.