f63c3c814e
* Add a first-class way of accessing caller's exports This commit is a continuation of #1237 and updates the API of `Func` to allow defining host functions which have easy access to a caller's memory in particular. The new APIs look like so: * The `Func::wrap*` family of functions was condensed into one `Func::wrap` function. * The ABI layer of conversions in `WasmTy` were removed * An optional `Caller<'_>` argument can be at the front of all host-defined functions now. The old way the wasi bindings looked up memory has been removed and is now replaced with the `Caller` type. The `Caller` type has a `get_export` method on it which allows looking up a caller's export by name, allowing you to get access to the caller's memory easily, and even during instantiation. * Add a temporary note * Move some docs
50 lines
1.8 KiB
Rust
50 lines
1.8 KiB
Rust
//! Small example of how to instantiate a wasm module that imports one function,
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//! showing how you can fill in host functionality for a wasm module.
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// You can execute this example with `cargo run --example hello`
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use anyhow::Result;
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use wasmtime::*;
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fn main() -> Result<()> {
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// Configure the initial compilation environment, creating the global
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// `Store` structure. Note that you can also tweak configuration settings
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// with a `Config` and an `Engine` if desired.
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println!("Initializing...");
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let store = Store::default();
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// Compile the wasm binary into an in-memory instance of a `Module`.
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println!("Compiling module...");
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let module = Module::from_file(&store, "examples/hello.wat")?;
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// Here we handle the imports of the module, which in this case is our
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// `HelloCallback` type and its associated implementation of `Callback.
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println!("Creating callback...");
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let hello_func = Func::wrap(&store, || {
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println!("Calling back...");
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println!("> Hello World!");
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});
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// Once we've got that all set up we can then move to the instantiation
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// phase, pairing together a compiled module as well as a set of imports.
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// Note that this is where the wasm `start` function, if any, would run.
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println!("Instantiating module...");
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let imports = [hello_func.into()];
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let instance = Instance::new(&module, &imports)?;
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// Next we poke around a bit to extract the `run` function from the module.
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println!("Extracting export...");
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let run = instance
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.get_export("run")
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.and_then(|e| e.func())
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.ok_or(anyhow::format_err!("failed to find `run` function export"))?
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.get0::<()>()?;
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// And last but not least we can call it!
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println!("Calling export...");
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run()?;
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println!("Done.");
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Ok(())
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}
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