Add example

Signed-off-by: knqyf263 <knqyf263@gmail.com>

examples/wasi/cat.go

@@ -1,4 +1,4 @@
-package wasi_example
+package main
 
 import (
 	"context"
@@ -9,11 +9,12 @@ import (
 	"os"
 
 	"github.com/tetratelabs/wazero"
+	expfs "github.com/tetratelabs/wazero/experimental/fs"
 	"github.com/tetratelabs/wazero/wasi"
 )
 
 // catFS is an embedded filesystem limited to test.txt
-//go:embed testdata/test.txt
+//go:embed testdata/test.txt testdata/sub/test.txt
 var catFS embed.FS
 
 // catWasm was compiled the TinyGo source testdata/cat.go
@@ -55,7 +56,33 @@ func main() {
 	// InstantiateModule runs the "_start" function which is what TinyGo compiles "main" to.
 	// * Set the program name (arg[0]) to "wasi" and add args to write "test.txt" to stdout twice.
 	// * We use "/test.txt" or "./test.txt" because WithFS by default maps the workdir "." to "/".
-	if _, err = r.InstantiateModule(ctx, code, config.WithArgs("wasi", os.Args[1])); err != nil {
+	mod, err := r.InstantiateModule(ctx, code, config.WithArgs("wasi", os.Args[1]))
+	if err != nil {
+		log.Panicln(err)
+	}
+
+	// Pass another fs.FS through context when calling a function
+	sub, err := fs.Sub(rooted, "sub")
+	if err != nil {
+		log.Panicln(err)
+	}
+
+	fsConfig := wazero.NewFSConfig().WithFS(sub)
+	subCtx, closer, err := expfs.WithFS(ctx, *fsConfig)
+	if err != nil {
+		log.Panicln(err)
+	}
+	defer closer.Close(subCtx)
+
+	subdir := mod.ExportedFunction("subdir")
+
+	// Call the function with the new filesystem and display "greet sub dir"
+	if _, err = subdir.Call(subCtx); err != nil {
+		log.Panicln(err)
+	}
+
+	// Call the function with the previous filesystem and display "greet filesystem"
+	if _, err = subdir.Call(ctx); err != nil {
 		log.Panicln(err)
 	}
 }

examples/wasi/cat_test.go

@@ -1,4 +1,4 @@
-package wasi_example
+package main
 
 import (
 	"testing"
@@ -12,5 +12,8 @@ import (
 //	go run cat.go ./test.txt
 func Test_main(t *testing.T) {
 	stdout, _ := maintester.TestMain(t, main, "cat", "./test.txt")
-	require.Equal(t, "greet filesystem\n", stdout)
+	require.Equal(t, `greet filesystem
+greet sub dir
+greet filesystem
+`, stdout)
 }

examples/wasi/testdata/cat.go

@@ -19,3 +19,14 @@ func main() {
 		os.Stdout.Write(bytes)
 	}
 }
+
+//export subdir
+func subdir() {
+	bytes, err := ioutil.ReadFile("./test.txt")
+	if err != nil {
+		os.Exit(1)
+	}
+
+	// Use write to avoid needing to worry about Windows newlines.
+	os.Stdout.Write(bytes)
+}

examples/wasi/testdata/sub/test.txt

@@ -0,0 +1 @@
+greet sub dir