Function ExampleWasiConfig

example_test.go:584–664

An example of linking WASI to the runtime in order to interact with the system. It uses the WAT code from https://github.com/bytecodealliance/wasmtime/blob/main/docs/WASI-tutorial.md#web-assembly-text-example

()

// An example of linking WASI to the runtime in order to interact with the system.
// It uses the WAT code from https://github.com/bytecodealliance/wasmtime/blob/main/docs/WASI-tutorial.md#web-assembly-text-example
func ExampleWasiConfig() {
	dir, err := os.MkdirTemp("", "out")
	if err != nil {
		log.Fatal(err)
	}
	defer os.RemoveAll(dir)
	stdoutPath := filepath.Join(dir, "stdout")

	engine := wasmtime.NewEngine()

	// Create our module
	wasm, err := wasmtime.Wat2Wasm(`
	(module
	  ;; Import the required fd_write WASI function which will write the given io vectors to stdout
	  ;; The function signature for fd_write is:
	  ;; (File Descriptor, *iovs, iovs_len, nwritten) -> Returns number of bytes written
	  (import "wasi_snapshot_preview1" "fd_write" (func $fd_write (param i32 i32 i32 i32) (result i32)))

	  (memory 1)
	  (export "memory" (memory 0))

	  ;; Write 'hello world\n' to memory at an offset of 8 bytes
	  ;; Note the trailing newline which is required for the text to appear
	  (data (i32.const 8) "hello world\n")

	  (func $main (export "_start")
	    ;; Creating a new io vector within linear memory
	    (i32.store (i32.const 0) (i32.const 8))  ;; iov.iov_base - This is a pointer to the start of the 'hello world\n' string
	    (i32.store (i32.const 4) (i32.const 12))  ;; iov.iov_len - The length of the 'hello world\n' string

	    (call $fd_write
	      (i32.const 1) ;; file_descriptor - 1 for stdout
	      (i32.const 0) ;; *iovs - The pointer to the iov array, which is stored at memory location 0
	      (i32.const 1) ;; iovs_len - We're printing 1 string stored in an iov - so one.
	      (i32.const 20) ;; nwritten - A place in memory to store the number of bytes written
	    )
	    drop ;; Discard the number of bytes written from the top of the stack
	  )
	)
	`)
	if err != nil {
		log.Fatal(err)
	}
	module, err := wasmtime.NewModule(engine, wasm)
	if err != nil {
		log.Fatal(err)
	}

	// Create a linker with WASI functions defined within it
	linker := wasmtime.NewLinker(engine)
	err = linker.DefineWasi()
	if err != nil {
		log.Fatal(err)
	}

	// Configure WASI imports to write stdout into a file, and then create
	// a `Store` using this wasi configuration.
	wasiConfig := wasmtime.NewWasiConfig()