Add `plugin.call_with_host_context` and `current_plugin.host_context`
methods, enabling per-call context to be looped from the guest invocation
to any host functions it calls. In an HTTP server environment, this enables
re-using a plugin across multiple requests while switching out backing
connections and user information in host functions. (Imagine a host
function, `update_user` -- previously the plugin would have to have been
aware of the user to pass to the host function. Now that information is
ambient.)
This is a backwards-compatible change and requires no changes to
existing plugins.
Implement by adding a global, mutable externref to the extism kernel.
Since most programming languages, including Rust, don't let you define
these natively, we accomplish this by using `wasm-merge` to combine the
kernel Wasm with Wasm generated by a WAT file containing only the
global.
(This pattern might be useful for other Wasm constructs we can't use
directly from Rust, like `v128` in argument parameters.)
Wasmtime requires extern refs to be `Any + Send + Sync + 'static`; we
additionally add `Clone`. I haven't tried this with an `Arc` directly,
but it should work at least for container structs that hold `Arc`'s
themselves.
- Adds benchmarking, run with `cargo bench` or `cargo criterion`
- Adds `MemoryRoot::pointer_in_bounds_fast` to do less precise bounds
checking in loads/stores
---------
Co-authored-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com>
Co-authored-by: zshipko <zshipko@users.noreply.github.com>
This PR adds the `kernel` directory which contains a port of the Extism
memory allocator compiled to WebAssembly and removes
`runtime/src/memory.rs` completely.
Being able to re-use memory functions as a WASM module allows us to
begin to experiment with porting Extism to new runtimes!
This is in a draft state while I'm verifying some of these changes.
