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Last active Jan 25, 2019
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Wasmer Rust Embedder App Example
extern crate wasmer_runtime;
use std::{fs::File, io::prelude::*, str};
use wasmer_runtime::{self as runtime, prelude::*};
fn main() {
// Read the wasm file produced by our sample application...
let mut wasm_file =
// ... and put it into a vector.
let mut wasm_bytes = Vec::new();
wasm_file.read_to_end(&mut wasm_bytes).unwrap();
// Compile our webassembly into a wasmer-runtime `Module`.
let module = runtime::compile(&wasm_bytes).unwrap();
// Let's define the import object used to import our function
// into our webassembly sample application.
// We've defined a macro that makes it super easy.
// The signature tells the runtime what the signature (the parameter
// and return types) of the function we're defining here is.
// The allowed types are `i32`, `u32`, `i64`, `u64`,
// `f32`, and `f64`.
// Make sure to check this carefully!
let import_object = imports! {
// Define the "env" namespace that was implicitly used
// by our sample application.
"env" => {
// name // func // signature
"print_str" => print_str<[u32, u32] -> []>,
// Here we go!
// Instantiate the module with the imports we just created
// to create, you guessed it, an `Instance`.
// You can create any number of instances with a single module.
let mut instance = module.instantiate(import_object).unwrap();
// At last, we can call the function exported by our webassembly
// sample application.
// Since our exported function doesn't receive any parameters,
// we just pass it an empty slice as the parameter list."hello_wasm", &[]).unwrap();
// Let's define our "print_str" function.
// The declaration must start with "extern" or "extern "C"".
extern "C" fn print_str(ptr: u32, len: u32, vmctx: &mut vm::Ctx) {
// Get a slice that maps to the memory currently used by the webassembly
// instance.
// Webassembly only supports a single memory for now,
// but in the near future, it'll support multiple.
// Therefore, we don't assume you always just want to access first
// memory and force you to specify the first memory.
let memory = vmctx.memory(0);
// Get a subslice that corresponds to the memory used by the string.
let str_slice = &memory[ptr as usize..(ptr + len) as usize];
// Convert the subslice to a `&str`.
let string = str::from_utf8(str_slice).unwrap();
// Print it!
println!("{}", string);
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