fixes arg handling

Signed-off-by: Adrian Cole <[email protected]>

examples/file_system_test.go

@@ -31,12 +31,16 @@ func Test_Cat(t *testing.T) {
 	stdoutBuf := bytes.NewBuffer(nil)
 	wasiConfig := wazero.NewWASIConfig().WithStdout(stdoutBuf)
 
-	// Next, configure a sand-boxed filesystem to include one file. We'll use that as the argument to `cat`.
+	// Next, configure a sand-boxed filesystem to include one file.
 	file := "cat.go" // arbitrary file
 	memFS := wazero.WASIMemFS()
 	err := writeFile(memFS, file, catGo)
 	require.NoError(t, err)
-	wasiConfig.WithPreopens(map[string]wasi.FS{".": memFS}).WithArgs(file)
+	wasiConfig.WithPreopens(map[string]wasi.FS{".": memFS})
+
+	// Since this runs a main function (_start in WASI), configure the arguments.
+	// Remember, arg[0] is the program name!
+	wasiConfig.WithArgs("cat", file)
 
 	// Now, instantiate WASI with the above configuration.
 	wasi, err := r.InstantiateModule(wazero.WASISnapshotPreview1WithConfig(wasiConfig))

examples/testdata/cat.go

@@ -4,10 +4,11 @@ import (
 	"os"
 )
 
-// main is the same as cat.
+// main is the same as cat: "concatenate and print files."
 func main() {
-	for _, file := range os.Args {
-		bytes, err := os.ReadFile(file)
+	// Start at arg[1] because args[0] is the program name.
+	for i := 1; i < len(os.Args); i++ {
+		bytes, err := os.ReadFile(os.Args[i])
 		if err != nil {
 			os.Exit(1)
 		}