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63 lines
2.4 KiB
63 lines
2.4 KiB
//! 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 wasmtime::*;
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struct MyState {
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name: String,
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count: usize,
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}
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fn main() -> Result<()> {
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// First the wasm module needs to be compiled. This is done with a global
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// "compilation environment" within an `Engine`. Note that engines can be
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// further configured through `Config` if desired instead of using the
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// default like this is here.
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println!("Compiling module...");
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let engine = Engine::default();
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let module = Module::from_file(&engine, "examples/hello.wat")?;
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// After a module is compiled we create a `Store` which will contain
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// instantiated modules and other items like host functions. A Store
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// contains an arbitrary piece of host information, and we use `MyState`
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// here.
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println!("Initializing...");
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let mut store = Store::new(
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&engine,
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MyState {
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name: "hello, world!".to_string(),
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count: 0,
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},
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);
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// Our wasm module we'll be instantiating requires one imported function.
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// the function takes no parameters and returns no results. We create a host
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// implementation of that function here, and the `caller` parameter here is
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// used to get access to our original `MyState` value.
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println!("Creating callback...");
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let hello_func = Func::wrap(&mut store, |mut caller: Caller<'_, MyState>| {
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println!("Calling back...");
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println!("> {}", caller.data().name);
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caller.data_mut().count += 1;
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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(&mut store, &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.get_typed_func::<(), ()>(&mut store, "run")?;
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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.call(&mut store, ())?;
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println!("Done.");
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Ok(())
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}
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