wasm_modules.md

Non-component model use

You can use wasm-bridge without the component model, but not many features are implemented.

Implemented features

• Load a module from bytes or from WAT text
• Instantiate a module with or without imports
• Get (typed) exported function and call it
• Multivalue returns from exported and imported functions
• Supported value types: i32, i64, u32, u64, f32, f64
• Access store's data from Caller (imported fn)

See the no_bindgen test folder for supported example usages.

Example usage

Here is an example of adding three using a WASM module compiled from WAT, using wasm-bridge version 0.1.1:

use wasm_bride::*;

fn add_three(number: i32) -> Result<i32> {
    let mut store = Store::<()>::default();

    let wat = r#"
      (module
        (func $add_three (export "add_three")
          (param $p0 i32) (result i32)
          (i32.add (local.get $p0) (i32.const 3))
        )
      )
    "#;
    let module = Module::new(store.engine(), wat.as_bytes())?;

    let instance = Instance::new(&mut store, &module, &[])?;
    let add_three_wasm = instance.get_typed_func::<i32, i32>(&mut store, "add_three")?;

    let result = add_three_wasm.call(&mut store, number)?;
    Ok(result)
}

Alternatively, watch the video tutorial:

Sync vs async methods

When running on the web, compiling and instantiation WASM modules syncly can result in an error.

Wasm-bridge provides async variants, which are safer to use and don't block the JS "thread" the code runs on.

These are, however, slightly different from the "normal" async functions that wasmtime provides, as described in this table:

Function	signature	feature	Desktop runtime	Web runtime
Module::new	sync	none	Calls wasmtime's Module::new	Calls the sync new WebAssembly.Module() constructor ❌
wasm_bridge::new_module_async	async	none	Calls wasmtime's Module::new	Calls the async WebAssembly.compile() function ✅
---	---	---	---	---
Instance::new	sync	none	Calls wasmtime's Instance::new	Calls the sync new WebAssembly.Instance() constructor ❌
Instance::new_async	async	async	Calls wasmtime's Instance::new_async	Calls the async new WebAssembly.instantiate() function ✅
wasm_bridge::new_instance_async	async	none	Calls wasmtime's Instance::new	Calls the async new WebAssembly.instantiate() function ✅
---	---	---	---	---
linker.instantiate	sync	none	Calls wasmtime's linker.instantiate	Calls the sync new WebAssembly.Instance() constructor ❌
linker.instantiate_async	async	async	Calls wasmtime's linker.instantiate_async	Calls the async new WebAssembly.instantiate() function ✅
wasm_bridge::instantiate_async	async	none	Calls wasmtime's linker.instantiate	Calls the async new WebAssembly.instantiate() function ✅
---	---	---	---	---
Component::new	sync	none	Calls wasmtime's Component::new	Calls the sync new WebAssembly.Module() constructor ❌
wasm_bridge::component::new_component_async	async	none	Calls wasmtime's Component::new	Calls the async WebAssembly.compile() function ✅

The advantage of the "custom" wasm-bridge methods is that they work even without the async feature flag.

The component functions require the component-model feature, but that would not fit into the table.