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.
Same as #471 for `main` branch
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Co-authored-by: zshipko <zshipko@users.noreply.github.com>
Closes#469
This PR adds a github workflow that is triggered by updates to the
`kernel/` directory or `runtime/src/extism-kernel.wasm` - it builds the
kernel, including using `wasm-strip` and makes a PR against any PR that
has a kernel module that doesn't match the expected output.
I had considered making this run when the PR is merged into main, but
this approach gives us a chance to run CI with the generated wasm file.
I think automatically adding a commit would be simpler, but this way
seems more transparent.
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Co-authored-by: zshipko <zshipko@users.noreply.github.com>
