chore(go): remove experimental FS API usage in Wasm (#3299)

Signed-off-by: Takeshi Yoneda <takeshi@tetrate.io>

pkg/module/memfs.go

@@ -0,0 +1,43 @@
+package module
+
+import (
+	"io"
+	"io/fs"
+	"path/filepath"
+
+	"golang.org/x/xerrors"
+
+	dio "github.com/aquasecurity/go-dep-parser/pkg/io"
+	"github.com/aquasecurity/memoryfs"
+)
+
+// memFS is a wrapper of memoryfs.FS and can change its underlying file system
+// at runtime. This implements fs.FS.
+type memFS struct {
+	current *memoryfs.FS
+}
+
+// Open implements fs.FS.
+func (m *memFS) Open(name string) (fs.File, error) {
+	return m.current.Open(name)
+}
+
+// initialize changes the underlying memory file system with the given file path and contents.
+//
+// Note: it is always to safe swap the underlying FS with this API since this is called only at the beginning of
+// Analyze interface call, which is not concurrently called per module instance.
+func (m *memFS) initialize(filePath string, content dio.ReadSeekerAt) (err error) {
+	memfs := memoryfs.New()
+	if err = memfs.MkdirAll(filepath.Dir(filePath), fs.ModePerm); err != nil {
+		return xerrors.Errorf("memory fs mkdir error: %w", err)
+	}
+	err = memfs.WriteLazyFile(filePath, func() (io.Reader, error) {
+		return content, nil
+	}, fs.ModePerm)
+	if err != nil {
+		return xerrors.Errorf("memory fs write error: %w", err)
+	}
+
+	m.current = memfs
+	return
+}

pkg/module/memfs_test.go

@@ -0,0 +1,33 @@
+package module
+
+import (
+	"io"
+	"os"
+	"strings"
+	"testing"
+
+	"github.com/stretchr/testify/require"
+)
+
+func TestMemFS(t *testing.T) {
+	m := &memFS{}
+	require.Nil(t, m.current)
+
+	const path, content = "/usr/foo/bar.txt", "my-content"
+	err := m.initialize(path, strings.NewReader(content))
+	require.NoError(t, err)
+	require.NotNil(t, m.current)
+
+	t.Run("happy", func(t *testing.T) {
+		f, err := m.Open(path)
+		require.NoError(t, err)
+		actual, err := io.ReadAll(f)
+		require.NoError(t, err)
+		require.Equal(t, content, string(actual))
+	})
+
+	t.Run("not found", func(t *testing.T) {
+		_, err = m.Open(path + "tmp")
+		require.ErrorIs(t, err, os.ErrNotExist)
+	})
+}

pkg/module/module.go

@@ -3,23 +3,20 @@ package module
 import (
 	"context"
 	"encoding/json"
-	"io"
 	"io/fs"
 	"os"
 	"path/filepath"
 	"regexp"
+	"sync"
 
 	"github.com/mailru/easyjson"
 	"github.com/samber/lo"
 	"github.com/tetratelabs/wazero"
 	"github.com/tetratelabs/wazero/api"
-	"github.com/tetratelabs/wazero/experimental"
 	wasi "github.com/tetratelabs/wazero/imports/wasi_snapshot_preview1"
 	"golang.org/x/exp/slices"
 	"golang.org/x/xerrors"
 
-	"github.com/aquasecurity/memoryfs"
-
 	"github.com/aquasecurity/trivy/pkg/fanal/analyzer"
 	"github.com/aquasecurity/trivy/pkg/log"
 	tapi "github.com/aquasecurity/trivy/pkg/module/api"
@@ -237,7 +234,9 @@ func marshal(ctx context.Context, m api.Module, malloc api.Function, v easyjson.
 }
 
 type wasmModule struct {
-	mod api.Module
+	mod   api.Module
+	memFS *memFS
+	mux   sync.Mutex
 
 	name          string
 	version       int
@@ -255,8 +254,8 @@ type wasmModule struct {
 }
 
 func newWASMPlugin(ctx context.Context, r wazero.Runtime, code []byte) (*wasmModule, error) {
-	// Combine the above into our baseline config, overriding defaults (which discard stdout and have no file system).
-	config := wazero.NewModuleConfig().WithStdout(os.Stdout).WithFS(memoryfs.New())
+	mf := &memFS{}
+	config := wazero.NewModuleConfig().WithStdout(os.Stdout).WithFS(mf)
 
 	// Create an empty namespace so that multiple modules will not conflict
 	ns := r.NewNamespace(ctx)
@@ -361,6 +360,7 @@ func newWASMPlugin(ctx context.Context, r wazero.Runtime, code []byte) (*wasmMod
 
 	return &wasmModule{
 		mod:           mod,
+		memFS:         mf,
 		name:          name,
 		version:       version,
 		requiredFiles: requiredFiles,
@@ -417,20 +417,14 @@ func (m *wasmModule) Analyze(ctx context.Context, input analyzer.AnalysisInput)
 	filePath := "/" + filepath.ToSlash(input.FilePath)
 	log.Logger.Debugf("Module %s: analyzing %s...", m.name, filePath)
 
-	memfs := memoryfs.New()
-	if err := memfs.MkdirAll(filepath.Dir(filePath), fs.ModePerm); err != nil {
-		return nil, xerrors.Errorf("memory fs mkdir error: %w", err)
-	}
-	err := memfs.WriteLazyFile(filePath, func() (io.Reader, error) {
-		return input.Content, nil
-	}, fs.ModePerm)
-	if err != nil {
-		return nil, xerrors.Errorf("memory fs write error: %w", err)
-	}
+	// Wasm module instances are not Goroutine safe, so we take look here since Analyze might be called concurrently.
+	// TODO: This is temporary solution and we could improve the Analyze performance by having module instance pool.
+	m.mux.Lock()
+	defer m.mux.Unlock()
 
-	// Pass memory fs to the analyze() function
-	ctx, closer := experimental.WithFS(ctx, memfs)
-	defer closer.Close(ctx)
+	if err := m.memFS.initialize(filePath, input.Content); err != nil {
+		return nil, err
+	}
 
 	inputPtr, inputSize, err := stringToPtrSize(ctx, filePath, m.mod, m.malloc)
 	if err != nil {