wasmer/lib/api

wasmer

Wasmer is the most popular WebAssembly runtime for Rust. It supports JIT (Just In Time) and AOT (Ahead Of Time) compilation as well as pluggable compilers suited to your needs.

It's designed to be safe and secure, and runnable in any kind of environment.

Usage

Here is a small example of using Wasmer to run a WebAssembly module written with its WAT format (textual format):

use wasmer::{Store, Module, Instance, Value, imports};

fn main() -> anyhow::Result<()> {
    let module_wat = r#"
    (module
    (type $t0 (func (param i32) (result i32)))
    (func $add_one (export "add_one") (type $t0) (param $p0 i32) (result i32)
        get_local $p0
        i32.const 1
        i32.add))
    "#;

    let store = Store::default();
    let module = Module::new(&store, &module_wat)?;
    // The module doesn't import anything, so we create an empty import object.
    let import_object = imports! {};
    let instance = Instance::new(&module, &import_object)?;

    let add_one = instance.exports.get_function("add_one")?;
    let result = add_one.call(&[Value::I32(42)])?;
    assert_eq!(result[0], Value::I32(43));

    Ok(())
}

Discover the full collection of examples.

Features

Wasmer is not only fast, but also designed to be highly customizable:

• Pluggable engines — An engine is responsible to drive the compilation process and to store the generated executable code somewhere, either:

  • in-memory (with wasmer-engine-universal),
  • in a native shared object file (with wasmer-engine-dylib, .dylib, .so, .dll), then load it with dlopen,
  • in a native static object file (with wasmer-engine-staticlib), in addition to emitting a C header file, which both can be linked against a sandboxed WebAssembly runtime environment for the compiled module with no need for runtime compilation.

• Pluggable compilers — A compiler is used by an engine to transform WebAssembly into executable code:

  • wasmer-compiler-singlepass provides a fast compilation-time but an unoptimized runtime speed,
  • wasmer-compiler-cranelift provides the right balance between compilation-time and runtime performance, useful for development,
  • wasmer-compiler-llvm provides a deeply optimized executable code with the fastest runtime speed, ideal for production.

• Headless mode — Once a WebAssembly module has been compiled, it is possible to serialize it in a file for example, and later execute it with Wasmer with headless mode turned on. Headless Wasmer has no compiler, which makes it more portable and faster to load. It's ideal for constrainted environments.

• Cross-compilation — Most compilers support cross-compilation. It means it possible to pre-compile a WebAssembly module targetting a different architecture or platform and serialize it, to then run it on the targetted architecture and platform later.

• Run Wasmer in a JavaScript environment — With the js Cargo feature, it is possible to compile a Rust program using Wasmer to WebAssembly. In this context, the resulting WebAssembly module will expect to run in a JavaScript environment, like a browser, Node.js, Deno and so on. In this specific scenario, there is no engines or compilers available, it's the one available in the JavaScript environment that will be used.

Wasmer ships by default with the Cranelift compiler as its great for development purposes. However, we strongly encourage to use the LLVM compiler in production as it performs about 50% faster, achieving near-native speeds.

Note: if one wants to use multiple compilers at the same time, it's also possible! One will need to import them directly via each of the compiler crates.

Read the documentation to learn more.

---

Made with ❤️ by the Wasmer team, for the community