Embed a wasm runtime into a standalone Rust app and allow wasm and host functions to call each other

Question

Is it possible to write a standalone Rust app like the following, compile it into 2 parts, one wasm and one native , and embed a wasm runtime (like wasmtime) into the final binary and the whole piece just work like a single app?

WasmEdge has a macro #[wasmedge_bindgen] that marks a wasm func, but nothing that makes a host function accessible in wasm runtime though.

#[make_a_wasm_func]
fn f1(i: i32)->i32{
    i+1
}


#[make_a_host_func_that_can_be_called_from_wasm]
fn f2(i: i32)->i32{
    f1(i)+2
} 

#[make_a_wasm_func]
fn f3(i:i32)-> i32{
    f2(i)+3
}

fn main(){
    let r=f3(1);
    println!("{}",r);   

}

The expected output is 7.

I am looking at some thing very similar and my understanding is that "host" functions need to be imported into the "wasm" part as "import objects". I understand this is probably not the answer you are looking for but I thought that I might add a little more context. — Deep
– Deep, Commented Aug 29, 2022 at 16:52
WasmEdge published a series of examples in this repo. The examples in the recent release cover some basic use cases, such as how to call a wasm library from the host. For your use case, Example 2, Example 2-1 and Example 4 could help you. — apepkuss
– apepkuss, Commented Feb 9, 2023 at 10:39

elfeiin · Accepted Answer · 2024-03-09 13:24:03Z

Maintainer of WasmEdge here. Hope the following example code can help you:

use wasmedge_sdk::{
    error::HostFuncError, host_function, params, Caller, ImportObjectBuilder, ValType, Vm, WasmVal,
    WasmValue,
};

#[host_function]
fn my_add(_caller: Caller, input: Vec<WasmValue>) -> Result<Vec<WasmValue>, HostFuncError> {
    // check the number of inputs
    if input.len() != 2 {
        return Err(HostFuncError::User(1));
    }

    // parse the first input of WebAssembly value type into Rust built-in value type
    let a = if input[0].ty() == ValType::I32 {
        input[0].to_i32()
    } else {
        return Err(HostFuncError::User(2));
    };

    // parse the second input of WebAssembly value type into Rust built-in value type
    let b = if input[1].ty() == ValType::I32 {
        input[1].to_i32()
    } else {
        return Err(HostFuncError::User(3));
    };

    let c = a + b;

    Ok(vec![WasmValue::from_i32(c)])
}

fn main() -> Result<(), Box<dyn std::error::Error>> {
    // create an import module
    let import = ImportObjectBuilder::new()
        .with_func::<(i32, i32), i32>("add", my_add)?
        .build("extern")?;

    // create a new vm with default config and register the import module into the vm.
    let res = Vm::new(None)?.register_import_module(import)?.run_func(
        Some("extern"),
        "add",
        params!(15, 51),
    )?;

    println!("add({}, {}) = {}", 15, 51, res[0].to_i32());

    Ok(())
}

In addition, add the following dependency in Cargo.toml:

[dependencies]
wasmedge-sdk = "0.7.1"

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