Example for using WASI in WasmEdge C API

This example is for passing the environment variables and command line arguments into the WASM environment through WASI.

Introduction

The rust library to compile into WASM is as following:

rust

use std::env;

#[no_mangle]
pub fn print_env() {
  println!("The env vars are as follows.");
  for (key, value) in env::vars() {
    println!("{}: {}", key, value);
  }

  println!("The args are as follows.");
  for argument in env::args() {
    println!("{}", argument);
  }
}

The print_env is the function to print the environment variables and the command line argument in the WASM virtual environment.

The example C program use the WasmEdge C API to initialize the WASI environment as following:

  /* The envs. */
  const char EnvStrs[] = {
      'E', 'N', 'V', '1', '=', 'V', 'A', 'L', '1', '\0',
      // ENV1=VAL1
      'E', 'N', 'V', '2', '=', 'V', 'A', 'L', '2', '\0',
      // ENV2=VAL2
      'E', 'N', 'V', '3', '=', 'V', 'A', 'L', '3', '\0'
      // ENV3=VAL3
  };
  const char *const Envs[] = {&EnvStrs[0], &EnvStrs[10], &EnvStrs[20]};

  /* Set the envs and args. */
  WasmEdge_ModuleInstanceContext *WasiCxt =
      WasmEdge_VMGetImportModuleContext(VMCxt, WasmEdge_HostRegistration_Wasi);
  WasmEdge_ModuleInstanceInitWASI(WasiCxt, argv, argc, Envs, 3, NULL, 0);

The command line arguments are set as the same as the args of the C program, and the environment variables are set as the list ENV1=VAL1, ENV2=VAL2, ENV3=VAL3.

Installation

Before trying this example, the WasmEdge installation after the version 0.10.0 is required.

bash

curl -sSf https://raw.githubusercontent.com/WasmEdge/WasmEdge/master/utils/install.sh | bash

Then you can build this example with linking the WasmEdge shared library.

bash

# In the current directory.
clang set_wasi_env.c -o set_wasi_env.out -lwasmedge

(Optional) Build the example WASM from rust

For building the WASM from the rust source, the following steps are required:

Install the rust and cargo.
Install the wasm32-wasip1 target: $ rustup target add wasm32-wasip1

bash

cd rust
cargo build --release --target=wasm32-wasip1
# The output wasm will be at `target/wasm32-wasip1/release/wasi_get_env.wasm`.
# Copy it to the same level of set_wasi_env.c
cp ./target/wasm32-wasip1/release/wasi_get_env.wasm ../

Run

bash

# Run in interpreter mode
./set_wasi_env.out

The standard output of this example will be the following:

bash

The env vars are as follows.
ENV1: VAL1
ENV2: VAL2
ENV3: VAL3
The args are as follows.
./set_wasi_env.out