Embed WASM Functions

In this example, we will demonstrate how to call a few simple WebAssembly functions from a Go app. The functions are written in Rust, and require complex call parameters and return values. The #[wasmedge_bindgen] macro is needed for the compiler tools to auto-generate the correct code to pass call parameters from Go to WebAssembly.

The WASM app in Rust

As we described here, the WebAssembly spec only supports a few simple data types out of the box. It does not support types such as string and array. To pass rich types in Go to WebAssembly, the compiler needs to convert them to simple integers. For example, it converts a string into an integer memory address and an integer length. The wasmedge_bindgen tool does this conversion automatically.

use num_integer::lcm;
use serde::{Deserialize, Serialize};
use sha3::{Digest, Keccak256, Sha3_256};
#[allow(unused_imports)]
use wasmedge_bindgen::*;
use wasmedge_bindgen_macro::*;

#[derive(Serialize, Deserialize, Debug)]
struct Point {
    x: f32,
    y: f32,
}

#[derive(Serialize, Deserialize, Debug)]
struct Line {
    points: Vec<Point>,
    valid: bool,
    length: f32,
    desc: String,
}

#[wasmedge_bindgen]
pub fn create_line(p1: String, p2: String, desc: String) -> String {
    let point1: Point = serde_json::from_str(&p1).unwrap();
    let point2: Point = serde_json::from_str(&p2).unwrap();
    let length = ((point1.x - point2.x) * (point1.x - point2.x)
        + (point1.y - point2.y) * (point1.y - point2.y))
        .sqrt();

    let valid = if length == 0.0 { false } else { true };

    let line = Line {
        points: vec![point1, point2],
        valid: valid,
        length: length,
        desc: desc,
    };

    return serde_json::to_string(&line).unwrap();
}

#[wasmedge_bindgen]
pub fn say(s: String) -> String {
    let r = String::from("hello ");
    return r + &s;
}

#[wasmedge_bindgen]
pub fn obfusticate(s: String) -> String {
    (&s).chars()
        .map(|c| match c {
            'A'..='M' | 'a'..='m' => ((c as u8) + 13) as char,
            'N'..='Z' | 'n'..='z' => ((c as u8) - 13) as char,
            _ => c,
        })
        .collect()
}

#[wasmedge_bindgen]
pub fn lowest_common_multiple(a: i32, b: i32) -> i32 {
    let r = lcm(a, b);
    return r;
}

#[wasmedge_bindgen]
pub fn sha3_digest(v: Vec<u8>) -> Vec<u8> {
    return Sha3_256::digest(&v).as_slice().to_vec();
}

#[wasmedge_bindgen]
pub fn keccak_digest(s: Vec<u8>) -> Vec<u8> {
    return Keccak256::digest(&s).as_slice().to_vec();
}

Compile the Rust code to Wasm

First, we will compile the Rust source code into WebAssembly bytecode functions.

git clone https://github.com/second-state/WasmEdge-go-examples.git
cd rust_bindgen_funcs
cargo build --release --target wasm32-wasi
# The output WASM will be target/wasm32-wasi/release/rust_bindgen_funcs_lib.wasm

The Go host app

The Go source code to run the WebAssembly function in WasmEdge is as follows. The Execute() function calls the WebAssembly function and passes the call parameters using the #[wasmedge_bindgen] convention.

package main

import (
  "fmt"
  "os"

  "github.com/second-state/WasmEdge-go/wasmedge"
  bindgen "github.com/second-state/wasmedge-bindgen/host/go"
)

func main() {
  // Expected Args[0]: program name (./bindgen_funcs)
  // Expected Args[1]: wasm or wasm-so file (rust_bindgen_funcs_lib.wasm))

  // Set not to print debug info
  wasmedge.SetLogErrorLevel()

  // Create configure
  var conf = wasmedge.NewConfigure(wasmedge.WASI)

  // Create VM with configure
  var vm = wasmedge.NewVMWithConfig(conf)

  // Init WASI
  var wasi = vm.GetImportModule(wasmedge.WASI)
  wasi.InitWasi(
    os.Args[1:],     // The args
    os.Environ(),    // The envs
    []string{".:."}, // The mapping preopens
  )

  vm.LoadWasmFile(os.Args[1])
  vm.Validate()
  // Instantiate the bindgen and vm
  bg := bindgen.New(vm)
  bg.Instantiate()

  // Run bindgen functions
  var res []interface{}
  var err error
  // create_line: array, array, array -> array (inputs are JSON stringified)
  res, _, err = bg.Execute("create_line", "{\"x\":1.5,\"y\":3.8}", "{\"x\":2.5,\"y\":5.8}", "A thin red line")
  if err == nil {
    fmt.Println("Run bindgen -- create_line:", res[0].(string))
  } else {
    fmt.Println("Run bindgen -- create_line FAILED")
  }
  // say: array -> array
  res, _, err = bg.Execute("say", "bindgen funcs test")
  if err == nil {
    fmt.Println("Run bindgen -- say:", res[0].(string))
  } else {
    fmt.Println("Run bindgen -- say FAILED")
  }
  // obfusticate: array -> array
  res, _, err = bg.Execute("obfusticate", "A quick brown fox jumps over the lazy dog")
  if err == nil {
    fmt.Println("Run bindgen -- obfusticate:", res[0].(string))
  } else {
    fmt.Println("Run bindgen -- obfusticate FAILED")
  }
  // lowest_common_multiple: i32, i32 -> i32
  res, _, err = bg.Execute("lowest_common_multiple", int32(123), int32(2))
  if err == nil {
    fmt.Println("Run bindgen -- lowest_common_multiple:", res[0].(int32))
  } else {
    fmt.Println("Run bindgen -- lowest_common_multiple FAILED")
  }
  // sha3_digest: array -> array
  res, _, err = bg.Execute("sha3_digest", []byte("This is an important message"))
  if err == nil {
    fmt.Println("Run bindgen -- sha3_digest:", res[0].([]byte))
  } else {
    fmt.Println("Run bindgen -- sha3_digest FAILED")
  }
  // keccak_digest: array -> array
  res, _, err = bg.Execute("keccak_digest", []byte("This is an important message"))
  if err == nil {
    fmt.Println("Run bindgen -- keccak_digest:", res[0].([]byte))
  } else {
    fmt.Println("Run bindgen -- keccak_digest FAILED")
  }

  bg.Release()
  conf.Release()
}

Build and run the WASM app from your Go host app

::note Make sure you have installed Go, WasmEdge, and WasmEdge Go SDK. ::

Next, let's build the Go application with the WasmEdge Go SDK.

go build

Run the Go application, and it will run the WebAssembly functions embedded in the WasmEdge runtime.

$ ./bindgen_funcs rust_bindgen_funcs/target/wasm32-wasi/release/rust_bindgen_funcs_lib.wasm
Run bindgen -- create_line: {"points":[{"x":1.5,"y":3.8},{"x":2.5,"y":5.8}],"valid":true,"length":2.2360682,"desc":"A thin red line"}
Run bindgen -- say: hello bindgen funcs test
Run bindgen -- obfusticate: N dhvpx oebja sbk whzcf bire gur ynml qbt
Run bindgen -- lowest_common_multiple: 246
Run bindgen -- sha3_digest: [87 27 231 209 189 105 251 49 159 10 211 250 15 159 154 181 43 218 26 141 56 199 25 45 60 10 20 163 54 211 195 203]
Run bindgen -- keccak_digest: [126 194 241 200 151 116 227 33 216 99 159 22 107 3 177 169 216 191 114 156 174 193 32 159 246 228 245 133 52 75 55 27]