Embed a standalone WASM app

The WasmEdge Go SDK can embed standalone WebAssembly applications — ie a Rust application with a main() function compiled into WebAssembly.

Our demo Rust application reads from a file. Note that the WebAssembly program’s input and output data are now passed by the STDIN and STDOUT.

  1. use std::env;
  2. use std::fs::File;
  3. use std::io::{self, BufRead};
  5. fn main() {
  6.   // Get the argv.
  7.   let args: Vec<String> = env::args().collect();
  8.   if args.len() <= 1 {
  9.     println!("Rust: ERROR - No input file name.");
  10.     return;
  11.   }
  13.   // Open the file.
  14.   println!("Rust: Opening input file \"{}\"...", args[1]);
  15.   let file = match File::open(&args[1]) {
  16.     Err(why) => {
  17.       println!("Rust: ERROR - Open file \"{}\" failed: {}", args[1], why);
  18.       return;
  19.     },
  20.     Ok(file) => file,
  21.   };
  23.   // Read lines.
  24.   let reader = io::BufReader::new(file);
  25.   let mut texts:Vec<String> = Vec::new();
  26.   for line in reader.lines() {
  27.     if let Ok(text) = line {
  28.       texts.push(text);
  29.     }
  30.   }
  31.   println!("Rust: Read input file \"{}\" succeeded.", args[1]);
  33.   // Get stdin to print lines.
  34.   println!("Rust: Please input the line number to print the line of file.");
  35.   let stdin = io::stdin();
  36.   for line in stdin.lock().lines() {
  37.     let input = line.unwrap();
  38.     match input.parse::<usize>() {
  39.       Ok(n) => if n > 0 && n <= texts.len() {
  40.         println!("{}", texts[n - 1]);
  41.       } else {
  42.         println!("Rust: ERROR - Line \"{}\" is out of range.", n);
  43.       },
  44.       Err(e) => println!("Rust: ERROR - Input \"{}\" is not an integer: {}", input, e),
  45.     }
  46.   }
  47.   println!("Rust: Process end.");
  48. }

Compile the application into WebAssembly.

$ cd rust_readfile $ cargo build --target wasm32-wasi # The output file will be target/wasm32-wasi/debug/rust_readfile.wasm

The Go source code to run the WebAssembly function in WasmEdge is as follows.

package main import ( "os" "github.com/second-state/WasmEdge-go/wasmedge" ) func main() { wasmedge.SetLogErrorLevel() var conf = wasmedge.NewConfigure(wasmedge.REFERENCE_TYPES) conf.AddConfig(wasmedge.WASI) var vm = wasmedge.NewVMWithConfig(conf) var wasi = vm.GetImportModule(wasmedge.WASI) wasi.InitWasi( os.Args[1:], // The args os.Environ(), // The envs []string{".:."}, // The mapping directories ) // Instantiate wasm. _start refers to the main() function vm.RunWasmFile(os.Args[1], "_start") vm.Release() conf.Release() }

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

go get github.com/second-state/WasmEdge-go/wasmedge@v0.10.0 go build

Run the Golang application.

`$ ./read_file rust_readfile/target/wasm32-wasi/debug/rust_readfile.wasm file.txt Rust: Opening input file "file.txt"... Rust: Read input file "file.txt" succeeded. Rust: Please input the line number to print the line of file. # Input "5" and press Enter. 5 # The output will be the 5th line offile.txt`: abcDEF_!@#$%^ # To terminate the program, send the EOF (Ctrl + D). ^D # The output will print the terminate message: Rust: Process end.

More examples can be found at the WasmEdge-go-examples GitHub repo.