70 lines
2.5 KiB
Rust
70 lines
2.5 KiB
Rust
//! Translation of hello example
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use anyhow::{ensure, format_err, Context as _, Result};
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use std::rc::Rc;
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use wasmtime::*;
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struct HelloCallback;
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impl Callable for HelloCallback {
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fn call(&self, _params: &[Val], _results: &mut [Val]) -> Result<(), Trap> {
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println!("Calling back...");
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println!("> Hello World!");
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Ok(())
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}
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}
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fn main() -> Result<()> {
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// Configure the initial compilation environment, creating more global
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// structures such as an `Engine` and a `Store`.
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println!("Initializing...");
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let engine = HostRef::new(Engine::default());
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let store = HostRef::new(Store::new(&engine));
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// Next upload the `*.wasm` binary file, which in this case we're going to
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// be parsing an inline text format into a binary.
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println!("Loading binary...");
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let binary = wat::parse_str(
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r#"
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(module
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(func $hello (import "" "hello"))
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(func (export "run") (call $hello))
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)
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"#,
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)?;
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// Compiler the `*.wasm` binary into an in-memory instance of a `Module`.
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println!("Compiling module...");
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let module = HostRef::new(Module::new(&store, &binary).context("> Error compiling module!")?);
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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_type = FuncType::new(Box::new([]), Box::new([]));
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let hello_func = HostRef::new(Func::new(&store, hello_type, Rc::new(HelloCallback)));
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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 = vec![hello_func.into()];
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let instance = Instance::new(&store, &module, imports.as_slice())
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.context("> Error instantiating module!")?;
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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 exports = instance.exports();
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ensure!(!exports.is_empty(), "> Error accessing exports!");
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let run_func = exports[0].func().context("> Error accessing exports!")?;
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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_func
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.borrow()
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.call(&[])
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.map_err(|e| format_err!("> Error calling function: {:?}", e))?;
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println!("Done.");
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Ok(())
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}
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