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.
use std::env;
use std::fs::File;
use std::io::{self, BufRead};
fn main() {
// Get the argv.
let args: Vec<String> = env::args().collect();
if args.len() <= 1 {
println!("Rust: ERROR - No input file name.");
return;
}
// Open the file.
println!("Rust: Opening input file \"{}\"...", args[1]);
let file = match File::open(&args[1]) {
Err(why) => {
println!("Rust: ERROR - Open file \"{}\" failed: {}", args[1], why);
return;
},
Ok(file) => file,
};
// Read lines.
let reader = io::BufReader::new(file);
let mut texts:Vec<String> = Vec::new();
for line in reader.lines() {
if let Ok(text) = line {
texts.push(text);
}
}
println!("Rust: Read input file \"{}\" succeeded.", args[1]);
// Get stdin to print lines.
println!("Rust: Please input the line number to print the line of file.");
let stdin = io::stdin();
for line in stdin.lock().lines() {
let input = line.unwrap();
match input.parse::<usize>() {
Ok(n) => if n > 0 && n <= texts.len() {
println!("{}", texts[n - 1]);
} else {
println!("Rust: ERROR - Line \"{}\" is out of range.", n);
},
Err(e) => println!("Rust: ERROR - Input \"{}\" is not an integer: {}", input, e),
}
}
println!("Rust: Process end.");
}
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 of
file.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.