⭐️ Instantiating a Wasm module
This example illustrates the basics of using Wasmer through a "Hello World"-like project.
In this example we will be building a "Hello World"-like project. WebAssembly only supports passing integers and floats directly right now, thus to keep it simple we will be writing a host application that calls the
add_one function of a guest Wasm module, which adds 1 to the value passed as a parameter, and returns the result.The goal here is to show you the basics of using Wasmer, we'll focus on the steps required to get an instance out of a Wasm module.
First we are going to want to initialize a new project. To do this we can navigate to our project folder, or create one. In this example, we will create a new project. Lets create it and navigate to it:
Rust
Go
Python
PHP
C/C++
Ruby
cargo new instance
cd instance
We have to modify
Cargo.toml to add the Wasmer dependencies as shown below:[dependencies]
# The Wasmer API
wasmer = "3.0"
mkdir wasmer-example-instance
cd wasmer-example-instance
go mod init github.com/$USER/wasmer-example-instance
mkdir wasmer-example-instance
cd wasmer-example-instance
pip install wasmer wasmer_compiler_cranelift
mkdir wasmer-example-instance
cd wasmer-example-instance
composer init --name=wasmer-project-instance
composer require wasm/wasm
mkdir wasmer-example-instance
cd wasmer-example-instance
vim Makefile
Let's create a simple
Makefile:CFLAGS = -g -I$(shell $(WASMER_DIR)/bin/wasmer config --includedir)
LDFLAGS = -Wl,-rpath,$(shell $(WASMER_DIR)/bin/wasmer config --libdir)
LDLIBS = $(shell $(WASMER_DIR)/bin/wasmer config --libs)
.SILENT: instance instance.o
instance: instance.o
.PHONY: clean
.SILENT: clean
clean:
rm -f instance.o instance
Wasmer C API includes the
wasmer.h header file that you need to include to start using Wasm in C.gem install wasmer
Now that we have everything set up, let's go ahead and try it out!
The first step will be to load the Wasm module we want to use. This is done by having its contents loaded as bytes:
Rust
Go
Python
PHP
C/C++
Ruby
let wasm_bytes = wat2wasm(br#"
(module
(type $add_one_t (func (param i32) (result i32)))
(func $add_one_f (type $add_one_t) (param $value i32) (result i32)
local.get $value
i32.const 1
i32.add)
(export "add_one" (func $add_one_f)))
"#)?;
Here we are using the text representation of the Wasm module. Wasmer wants to have a binary representation of the module so we have to use
wat2wasm to do the translation.wasmBytes := []byte(`
(module
(type $add_one_t (func (param i32) (result i32)))
(func $add_one_f (type $add_one_t) (param $value i32) (result i32)
local.get $value
i32.const 1
i32.add)
(export "add_one" (func $add_one_f)))
`)
wasm_bytes = wat2wasm(
"""
(module
(type $add_one_t (func (param i32) (result i32)))
(func $add_one_f (type $add_one_t) (param $value i32) (result i32)
local.get $value
i32.const 1
i32.add)
(export "add_one" (func $add_one_f)))
"""
)
$wasmBytes = Wasm\Wat::wasm(<<<'WAT'
(module
(type $add_one_t (func (param i32) (result i32)))
(func $add_one_f (type $add_one_t) (param $value i32) (result i32)
local.get $value
i32.const 1
i32.add)
(export "add_one" (func $add_one_f)))
WAT);
const char *wat_string =
"(module\n"
" (type $add_one_t (func (param i32) (result i32)))\n"
" (func $add_one_f (type $add_one_t) (param $value i32) (result i32)\n"
" local.get $value\n"
" i32.const 1\n"
" i32.add)\n"
" (export \"add_one\" (func $add_one_f)))";
wasm_byte_vec_t wat;
wasm_byte_vec_new(&wat, strlen(wat_string), wat_string);
wasm_byte_vec_t wasm_bytes;
wat2wasm(&wat, &wasm_bytes);
wasm_bytes = Wasmer::wat2wasm(
(<<~WAST)
(module
(type $add_one_t (func (param i32) (result i32)))
(func $add_one_f (type $add_one_t) (param $value i32) (result i32)
local.get $value
i32.const 1
i32.add)
(export "add_one" (func $add_one_f)))
WAST
)
Let's assume we have the binary version of the module (i.e the
.wasm file), here is how we would have loaded it:Rust
Go
Python
PHP
C/C++
Ruby
let wasm_bytes = std::fs::read("./path/to/module.wasm")?;
wasmBytes, err := ioutil.ReadFile("./path/to/module.wasm")
wasmBytes = open('./path/to/module.wasm', 'rb').read()
$wasmBytes = file_get_contents('./path/to/module.wasm');
if (false === $wasmBytes) {
echo '> Error loading module!'.PHP_EOL;
exit(1);
}
FILE* file = fopen("module.wasm", "rb");
if (!file) {
printf("> Error loading module!\n");
return 1;
}
fseek(file, 0L, SEEK_END);
size_t file_size = ftell(file);
fseek(file, 0L, SEEK_SET);
wasm_byte_vec_t wasm_bytes;
wasm_byte_vec_new_uninitialized(&wasm_bytes, file_size);
if (fread(wasm_bytes.data, file_size, 1, file) != 1) {
printf("> Error loading module!\n");
return 1;
}
fclose(file);
file = File.expand_path "greet.wasm", File.dirname(__FILE__)
bytes = IO.read file, mode: "rb"
The next step will be to compile the module. To do this, we'll need two things: the Wasm module as bytes and a
Store.The
Store is a representation of the actual state of the module: it represents the state of every entity in the module during its lifecycle. It also holds the engine which is what will be used to actually compile the module.Here is how we can create the store and compile the module:
Rust
Go
Python
PHP
C/C++
Ruby
let mut store = Store::default();
let module = Module::new(&store, wasm_bytes)?;
We are creating a store using the default settings provided by Wasmer. In some cases, you may want to use a specific compiler. Here is how you would do:
let compiler_config = Cranelift::default();
let mut store = Store::new(compiler_config);
let module = Module::new(&store, wasm_bytes)?;
We created a store with the Cranelift compiler with its default configuration. These are good defaults but it will be a good thing to adapt this configuration to your needs.
engine := wasmer.NewEngine()
store := wasmer.NewStore(engine)
module, err := wasmer.NewModule(store, wasmBytes)
if err != nil {
fmt.Println("Failed to compile module:", err)
}
from wasmer_compiler_cranelift import Compiler
engine = engine.JIT(Compiler)
store = Store(engine)
module = Module(store, wasm_bytes)
$engine = Wasm\Engine::new();
$store = Wasm\Store::new($engine);
$module = Wasm\Module::new($store, $wasmBytes);
wasm_engine_t* engine = wasm_engine_new();
wasm_store_t* store = wasm_store_new(engine);
wasm_module_t* module = wasm_module_new(store, &wasm_bytes);
if (!module) {
printf("> Error compiling module!\n");
return 1;
}
store = Wasmer::Store.new
module_ = Wasmer::Module.new store, wasm_bytes
raise "Error" unless module
We are now close to having the module run in our Rust host.
The last step will be to create an
Instance out of the Wasm module. As for the previous step, here we need more than just the compiled module: we also need to define imports.In fact, Wasm modules can define entities they need to work properly. These are called imports. In this example we don't need any of them but we still need to define an empty set and use it to instantiate the module:
Rust
Go
Python
PHP
C/C++
Ruby
let imports = imports! {};
let instance = Instance::new(&mut store, &module, &imports)?;
importObject := wasmer.NewImportObject()
instance, err := wasmer.NewInstance(module, importObject)
instance = Instance(module)
$instance = Wasm\Instance::new($store, $module);
wasm_extern_vec_t imports = WASM_EMPTY_VEC;
wasm_instance_t* instance = wasm_instance_new(store, module, &imports, NULL);
if (!instance) {
printf("> Error instantiating module %d!\n");
return 1;
}
import_object = Wasmer::ImportObject.new
instance = Wasmer::Instance.new module_, import_object
raise "Error" unless instance
We now have everything we need to run the Wasm module, let's do it!
Rust
Go
Python
PHP
C/C++
Ruby
You should be able to run it using the
cargo run command. The output should look like this:Compiling module...
Instantiating module...
Calling `add_one` function...
Results of `add_one`: 2
git clone https://github.com/wasmerio/wasmer.git
cd wasmer
cargo run --example instance --release --features "cranelift"
You should be able to run it using the
go run main.go command. The output should look like this:Compiling module...
Instantiating module...
Calling `add_one` function...
Results of `add_one`: 2
git clone https://github.com/wasmerio/wasmer-go.git
cd wasmer-go
go test examples/example_instance_test.go
You should be able to run it using the
python instance.py command.git clone https://github.com/wasmerio/wasmer-python.git
cd wasmer-python
python examples/instance.py
You should be able to run it using the
php instance.php command.git clone https://github.com/wasmerio/wasmer-php.git
cd wasmer-php
make EXAMPLE=instance test-doc-examples
You should be able to run it using the
make clean instance && ./instance command. The output should look like this:Creating the store...
Compiling module...
Creating imports...
Instantiating module...
Retrieving exports...
Calling `add_one` function...
Results of `add_one`: 2
git clone https://github.com/wasmerio/wasmer.git
cd wasmer/lib/c-api/examples/instance.c
make clean instance
./instance
You should be able to run it using the
ruby instance.rb command.git clone https://github.com/wasmerio/wasmer-ruby.git
cd wasmer-ruby
ruby examples/instance.rb
Last modified 3mo ago