In this example we'll be using a sample Wasm module which exports some entities and requires us to also import some of them.
The goal here is to give you an idea of how to work with imports and exports. We won't go into the details of each entities, they'll be covered in more details in the other examples.
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:
The final Rust code for this example can be found on Github: imports_exports.rs.
Please take a look at the setup steps for Rust.
cargo new imports-exportscd imports-exports
We have to modify Cargo.toml
to add the Wasmer dependencies as shown below:
[dependencies]# The Wasmer APIwasmer = "1.0"
The final Go code for this example can be found on Github: imports_exports.go.
Please take a look at the setup steps for Go.
mkdir wasmer-example-imports-exportscd wasmer-example-imports-exportsgo mod init github.com/$USER/wasmer-example-imports-exports
The final Python code for this example can be found on Github: imports_exports.py.
Please take a look at the setup steps for Python.
mkdir wasmer-example-imports-exportscd wasmer-example-imports-exportspip install wasmer wasmer_compiler_cranelift
The final C code for this example can be found on Github: imports-exports.c.
Please take a look at the setup steps for C/C++.
mkdir wasmer-example-imports-exportscd wasmer-example-imports-exportsvim Makefile
Let's create a simple Makefile
:
CFLAGS = -g -I$(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: imports-exports imports-exports.oimports-exports: imports-exports.o.PHONY: clean.SILENT: cleanclean:rm -f imports-exports.o imports-exports
Now that we have everything set up, let's go ahead and try it out!
When a Wasm modules declares imports you will have to make them available before you can instantiate the module. Our first task will be to create the required entities.
The module we are using needs two imports:
A function named host_function
in a namespace with an empty name;
A global named host_global
in the env
namespace.
Let's create the import object:
let import_object = imports! {"" => {"host_function" => host_function,},"env" => {"host_global" => host_global,},};
importObject := wasmer.NewImportObject()importObject.Register("",map[string]wasmer.IntoExtern{"host_function": hostFunction,},)importObject.Register("env",map[string]wasmer.IntoExtern{"host_global": hostGlobal,},)
import_object = ImportObject()import_object.register("",{"host_function": host_function,})import_object.register("env",{"host_global": host_global,})
wasm_functype_t* host_func_type = wasm_functype_new_0_1(wasm_valtype_new_i32());wasm_func_t* host_func = wasm_func_new(store, host_func_type, host_func_callback);wasm_functype_delete(host_func_type);wasm_globaltype_t* host_global_type = wasm_globaltype_new(wasm_valtype_new(WASM_F32), WASM_CONST);wasm_val_t host_global_val = WASM_I32_VAL(42);wasm_global_t* host_global = wasm_global_new(store, host_global_type, &host_global_val);wasm_globaltype_delete(host_global_type);wasm_extern_t* externs[] = {wasm_func_as_extern(host_func),wasm_global_as_extern(host_global)};wasm_extern_vec_t import_object = WASM_ARRAY_VEC(externs);
Now that we have our import object ready, we'll need to use it when instantiating the module:
let instance = Instance::new(&module, &import_object)?;
instance, err := wasmer.NewInstance(module, importObject)
instance = Instance(module, import_object)
wasm_instance_t* instance = wasm_instance_new(store, module, &import_object, NULL);
That's it! Easy right?
We did not go into the details of how to create the imported entities, we encourage you to read other examples to know more about this:
Let's have a look at our module again: it exports some entities for us in our host program:
A function named guest_function
;
A global name guest_global
;
A table name guest_table
;
A memory named guest_memory
.
To get these entities we'll use the exports API:
let function = instance.exports.get::<Function>("guest_function")?;let global = instance.exports.get::<Global>("guest_global")?;let memory = instance.exports.get::<Memory>("guest_memory")?;let table = instance.exports.get::<Table>("guest_table")?;
function, err := instance.Exports.GetFunction("guest_function")if err != nil {panic(fmt.Sprintln("Failed to get the exported function:", err))}global, err := instance.Exports.GetGlobal("guest_global")if err != nil {panic(fmt.Sprintln("Failed to get the exported global:", err))}table, err := instance.Exports.GetTable("guest_table")if err != nil {panic(fmt.Sprintln("Failed to get the exported table:", err))}memory, err := instance.Exports.GetMemory("guest_memory")if err != nil {panic(fmt.Sprintln("Failed to get the exported memory:", err))}
function = instance.exports.guest_functionglobal = instance.exports.guest_globalmemory = instance.exports.guest_memorytable = instance.exports.guest_table
wasm_func_t* func = wasm_extern_as_func(exports.data[0]);if (func == NULL) {printf("> Failed to get the exported function!\n");return 1;}wasm_global_t* global = wasm_extern_as_global(exports.data[1]);if (global == NULL) {printf("> Failed to get the exported global!\n");return 1;}wasm_table_t* table = wasm_extern_as_table(exports.data[2]);if (table == NULL) {printf("> Failed to get the exported table!\n");return 1;}wasm_memory_t* memory = wasm_extern_as_memory(exports.data[3]);if (memory == NULL) {printf("> Failed to get the exported memory!\n");return 1;}
Again, we'll not cover how to use these entities here as this is the topic of other, more detailed, examples:
We now have everything we need to run the Wasm module, let's do it!
You should be able to run it using the cargo run
command. The output should look like this:
Compiling module...Creating the imported function...Creating the imported global...Instantiating module...Getting the exported function...Got exported function of type: FunctionType { params: [], results: [I32] }Getting the exported global...Got exported global of type: GlobalType { ty: I32, mutability: Const }Getting the exported memory...Got exported memory of type: MemoryType { minimum: 1 pages, maximum: None, shared: false }Getting the exported table...Got exported table of type: TableType { ty: FuncRef, minimum: 1, maximum: Some(1) }
If you want to run the examples from the Wasmer repository codebase directly, you can also do:
git clone https://github.com/wasmerio/wasmer.gitcd wasmercargo run --example imports-exports --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...Creating the imported function...Creating the imported global...Instantiating module...Getting the exported function...Got the exported function: func(...interface {}) (interface {}, error)Getting the exported global...Got the exported global: *wasmer.GlobalGetting the exported memory...Got the exported memory: *wasmer.MemoryGetting the exported table...Got the exported table: *wasmer.Table
If you want to run the examples from the Wasmer repository codebase directly, you can also do:
git clone https://github.com/wasmerio/wasmer-go.gitcd wasmer-gogo test examples/example_imports_exports_test.go
You should be able to run it using the python imports_exports.py
command.
If you want to run the examples from the Wasmer repository codebase directly, you can also do:
git clone https://github.com/wasmerio/wasmer-python.gitcd wasmer-pythonpython examples/imports_exports.py
You should be able to run it using the make clean imports-exports && ./imports-exports
command. The output should look like this:
Creating the store...Compiling module...Creating the imported function...Creating the imported global...Instantiating module...Retrieving exports...Retrieving the exported function...Got the exported function: 0x7f9317e05e00Retrieving the exported global...Got the exported global: 0x7f9317e05e90Retrieving the exported table...Got the exported table: 0x7f9317e05ec0Retrieving the exported memory...Got the exported memory: 0x7f9317e05ef0
If you want to run the examples from the Wasmer repository codebase directly, you can also do:
git clone https://github.com/wasmerio/wasmer.gitcd wasmer/lib/c-api/examples/imports-exports.cmake clean imports-exports./imports-exports