Wasmer is a WASM runtime coded in Rust, so it is really easy to embed the runtime inside you own Rust programs. The library is great, but its website and docs seems to be targeting its use as a CLI tool and not as a library.

If you dig a little bit you will find a link to the wasmer-runtime docs, which is good to look at documentation of specific components of the library, but it is far from an introduction to its features.

To really see what the Wasmer is about we must dive into the examples.

Trying to make sense of various examples may be a little time consuming, and that is where this post series comes in, giving an easy to follow introduction to using the Wasmer library and to WASM in general.

Wasmer Basics

We can summarize most of the examples in 5 steps:

// 1. Get the WASM code
let wasm_bytes = get_wasm_bytes();

// 2. Setup the runtime
let compiler_config = Cranelift::default();
let engine = JIT::new(compiler_config).engine();
let store = Store::new(&engine);

// 3. Compile the WASM code into a Module
let module = Module::new(&store, wasm_bytes)?;

// 4. Create an instance of the Module
let import_object = imports! {};
let instance = Instance::new(&module, &import_object)?;

// 5. Get the exported function reference and call it
let sum = instance.exports.get_function("sum")?;
let results = sum.call(&[Value::I32(1), Value::I32(2)])?;

Step 1: The WASM Code

First we need to get our WASM code. The code is just a sequence of bytes, in the Wasmer example it is inlined into the code, but you can read it at runtime from anywhere.

Step 2: WASM Runtime

To run this code we first need to compile it, we will use the just-in-time (JIT) engine from to build our code at runtime, there are other options but I will not explore them here.

Step 3: The Module

The chosen engine is used to build the WASM code into a Module.

Step 4: Instantiation

This Module can be instantiated.

Step 5: Use The Instance

Finally, we can get references to the WASM module exported data, this allows us to call functions that will be run inside the Wasmer sandboxed environment.