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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.
4 lines
81 B
Plaintext
4 lines
81 B
Plaintext
(module
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(global (export "extism_context") (mut externref) (ref.null extern))
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)
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