wasm-wasmtime

# Install
curl https://wasmtime.dev/install.sh -sSf | bash

# Run a WASM module
wasmtime hello.wasm

# Run with WASI arguments
wasmtime prog.wasm -- arg1 arg2

# Pre-open directories (WASI filesystem sandbox)
wasmtime --dir /tmp::/ prog.wasm    # map host /tmp to WASI root

# Pass environment variables
wasmtime --env HOME=/home/user prog.wasm

# Invoke specific exported function
wasmtime run --invoke add math.wasm 3 4

# Inspect exports
wasmtime explore math.wasm    # interactive explorer
wasmtime inspect math.wasm    # show all exports/imports

# Compile to native ahead-of-time
wasmtime compile prog.wasm -o prog.cwasm
wasmtime run prog.cwasm

# wasmtime supports WASI p2 natively
wasmtime --wasi-modules experimental-wasi-http prog.wasm

# Key WASI interfaces (WIT)
# wasi:filesystem — file and directory access
# wasi:sockets — TCP/UDP networking (preview2)
# wasi:http — HTTP client/server (experimental)
# wasi:cli — stdin/stdout/stderr, environment
# wasi:random — secure random numbers
# wasi:clocks — system and monotonic clocks

# Cargo.toml
[dependencies]
wasmtime = "24"
wasmtime-wasi = "24"
anyhow = "1"

use wasmtime::*;
use wasmtime_wasi::WasiCtxBuilder;

fn main() -> anyhow::Result<()> {
    // Create engine with default config
    let engine = Engine::default();

    // Load and compile WASM module
    let module = Module::from_file(&engine, "prog.wasm")?;

    // Set up WASI context
    let wasi = WasiCtxBuilder::new()
        .inherit_stdio()
        .inherit_env()
        .preopened_dir("/tmp", "/")?
        .build();

    // Create a store (holds WASM state)
    let mut store = Store::new(&engine, wasi);

    // Instantiate the module
    let instance = Instance::new(&mut store, &module, &[])?;

    // Call an exported function
    let add = instance.get_typed_func::<(i32, i32), i32>(&mut store, "add")?;
    let result = add.call(&mut store, (3, 4))?;
    println!("Result: {result}");

    Ok(())
}

use wasmtime::*;

let mut config = Config::default();
config.consume_fuel(true);    // enable fuel consumption

let engine = Engine::new(&config)?;
let module = Module::from_file(&engine, "untrusted.wasm")?;

let mut store = Store::new(&engine, ());
store.set_fuel(1_000_000)?;   // allow 1M instructions

let instance = Instance::new(&mut store, &module, &[])?;
let run = instance.get_typed_func::<(), ()>(&mut store, "run")?;

match run.call(&mut store, ()) {
    Ok(_) => println!("Completed, fuel remaining: {}", store.get_fuel()?),
    Err(e) if e.to_string().contains("all fuel consumed") => {
        println!("Timed out (fuel exhausted)");
    }
    Err(e) => eprintln!("Error: {e}"),
}

// math.wit — interface definition
package example:math@1.0.0;

interface calculator {
    add: func(a: s32, b: s32) -> s32;
    sqrt: func(x: f64) -> f64;
}

world math-world {
    export calculator;
}

# Install component toolchain
cargo install wasm-tools cargo-component

# Create a Rust component
cargo component new --lib math-component
# Implement the WIT interface in src/lib.rs

# Build component
cargo component build --release

# Run with wasmtime component
wasmtime run math-component.wasm

// Embed a component in Rust
use wasmtime::component::*;

wasmtime::component::bindgen!({
    world: "math-world",
    path: "math.wit",
});

let component = Component::from_file(&engine, "math.wasm")?;
let (calculator, _) = MathWorld::instantiate(&mut store, &component, &linker)?;
let result = calculator.call_add(&mut store, 3, 4)?;

# Build WASM with debug info (Rust)
cargo build --target wasm32-wasi    # debug profile includes DWARF by default

# Run with source-level debugging
WASMTIME_BACKTRACE_DETAILS=1 wasmtime prog.wasm

# Full DWARF stack traces
wasmtime --debug-info prog.wasm 2>&1

# GDB with WASM (wasmtime dev build)
wasmtime debug prog.wasm   # experimental

# wasm-tools for inspection
wasm-tools print prog.wasm | head -50     # disassemble to WAT
wasm-tools validate prog.wasm             # validate WASM binary

;; GC-enabled module (toolchain dependent)
(struct $point (field (mut f32) x) (field (mut f32) y))

# wasm-tools with GC support
wasm-tools validate --features gc module.wasm
wasmtime run --wasm gc module.wasm

# Requires SharedArrayBuffer in JS hosts; WASI pthreads in native hosts
# Compile with threading enabled (Clang/Rust wasm32-wasi-threads)
clang --target=wasm32-wasi -pthread -matomics -mbulk-memory -o prog.wasm prog.c

# Current wasmtime enables threads + shared-memory by default (see stability-wasm-proposals)
wasmtime run prog.wasm

(try (do $exn)
  (throw $exn)
  (catch $exn (local.get 0) (return)))

# Exception handling enabled by default in current wasmtime releases
wasmtime run module.wasm

config.wasm_exceptions(true);  // usually on by default in recent wasmtime

# wasmtime 17+ supports component model / WASI p2 (see examples-wasip2.html)
wasmtime run component.wasm

# wit-bindgen generates host/guest bindings from WIT files
wit-bindgen rust ./deps/wasi-cli.wit

// High-performance embedding config
let mut config = Config::default();
config.cranelift_opt_level(OptLevel::SpeedAndSize);
config.parallel_compilation(true);
config.cache_config_load_default()?;    // disk cache for compiled modules

// Ahead-of-time compilation for production
// 1. Pre-compile in build pipeline
let serialized = module.serialize()?;
std::fs::write("prog.cwasm", &serialized)?;

// 2. Load pre-compiled at runtime (zero compilation cost)
let module = unsafe { Module::deserialize_file(&engine, "prog.cwasm")? };