Hello world

Before we start, ensure you have Rust and WasmEdge installed.

A simple main app

The Hello World example is a standalone Rust application that can be executed by the WasmEdge CLI. The full source code for the Rust main.rs file is as follows. It echoes the command line arguments passed to this program at runtime.

fn main() {
  let s : &str = "Hello WasmEdge!";
  println!("{}", s);
}

Build the WASM bytecode:

cargo build --target wasm32-wasi --release

We will use the wasmedge command to run the program.

$ wasmedge target/wasm32-wasi/release/hello.wasm
Hello WasmEdge

A simple function

The code

The add example is a Rust library function that can be executed by the WasmEdge CLI in the reactor mode.

The full source code for the Rust lib.rs file is as follows. It provides a simple add() function.

#[no_mangle]
pub fn add(a: i32, b: i32) -> i32 {
  return a + b;
}

Build the WASM bytecode

cargo build --target wasm32-wasi --release

Run the application from command line

We will use wasmedge in reactor mode to run the program. We pass the function name and its input parameters as command line arguments.

$ wasmedge --reactor target/wasm32-wasi/release/add.wasm add 2 2
4

Pass parameters with complex data types

Of course, in most cases, you will not call functions using CLI arguments. Instead, you will probably need to use a [language SDK from WasmEdge] to call the function, pass call parameters, and receive return values. Below are some SDK examples for complex call parameters and return values.

• Use wasmedge-bindgen in a Go host app
• Use direct memory passing in a Go host app

Improve the performance

If we don't have extra notes for AoT, all the WASM file will be executed in the interpreter mode, which is much slower. To achieve native Rust performance for those applications, you could use the wasmedge compile command to AOT compile the wasm program and then run it with the wasmedge command.

$ wasmedge compile hello.wasm hello_aot.wasm

$ wasmedge hello_aot.wasm second state
hello
second
state

For the --reactor mode,

$ wasmedge compile add.wasm add_aot.wasm

$ wasmedge --reactor add_aot.wasm add 2 2
4