Test Framework Base

[agiachris]

This pull request contains the base framework for the ABI test harness, enabling the user to set low-level and high-level expectations over a variety host-side functions and all functions exported by the proxy-wasm module. Remaining work includes the extension of this framework to support all host-side functions, and the associated low-level and high-level expectation settings.

[PiotrSikora]

cc @gbrail

[PiotrSikora]

Could you run rustfmt and clippy over the codebase?

$ rustup toolchain install stable --component clippy --component rustfmt
$ cargo clippy --target=wasm32-unknown-unknown --release --all-targets
$ cargo fmt

[PiotrSikora]

LGTM, a few style comments.

[PiotrSikora]

Could you make them part of the same comment section, using the same style-prefix?

[PiotrSikora]

I've opened a few issues to follow-up, but this looks great, thanks!

[jplevyak]

Looks good to me.

Would it be possible to use Rust macros to avoid some of the repetition? You end up creating a lot of small objects the sole purpose of which is to handle the expecting -> returning idiom which would seem amenable to automation through macros.

[jplevyak]

FYI: the VM contest which is used only for allocating memory is typically 1 whereas the first root context is typically 2. This isn't part of the ABI, but it is part of the Envoy host implementation.

[PiotrSikora]

Uhm, is that a recent change? It used to be that the root context was always created with parent_context_id = 0, and that's how some SDKs are inferring the type of the context to create (RootContext if parent_context_id == 0, {Http,Stream}Context otherwise).