fix(engine): preserve readlink errno for fs mounts

engine/wasi_fs.go

@@ -0,0 +1,27 @@
+package engine
+
+import (
+	"io/fs"
+
+	"github.com/tetratelabs/wazero"
+	experimentalsys "github.com/tetratelabs/wazero/experimental/sys"
+	wazerosysfs "github.com/tetratelabs/wazero/experimental/sysfs"
+)
+
+type readOnlyMountFS struct {
+	*wazerosysfs.AdaptFS
+}
+
+func withReadOnlyFSMount(cfg wazero.FSConfig, fsys fs.FS, guest string) wazero.FSConfig {
+	sysCfg := cfg.(wazerosysfs.FSConfig)
+	return sysCfg.WithSysFSMount(&readOnlyMountFS{
+		AdaptFS: &wazerosysfs.AdaptFS{FS: fsys},
+	}, guest)
+}
+
+func (f *readOnlyMountFS) Readlink(path string) (string, experimentalsys.Errno) {
+	if _, errno := f.Lstat(path); errno != 0 {
+		return "", errno
+	}
+	return "", experimentalsys.EINVAL
+}

engine/wazero.go

@@ -117,7 +117,7 @@ func applyWASIConfig(mc wazero.ModuleConfig, cfg *InstanceConfig) wazero.ModuleC
 		for _, mnt := range cfg.Mounts {
 			switch {
 			case mnt.FS != nil:
-				fsCfg = fsCfg.WithFSMount(mnt.FS, mnt.Guest)
+				fsCfg = withReadOnlyFSMount(fsCfg, mnt.FS, mnt.Guest)
 			case mnt.ReadOnly:
 				fsCfg = fsCfg.WithReadOnlyDirMount(mnt.Host, mnt.Guest)
 			default:

engine/wazero_test.go

@@ -5,6 +5,7 @@ import (
 	"os"
 	"strings"
 	"testing"
+	"testing/fstest"
 
 	"github.com/wippyai/wasm-runtime/wat"
 )
@@ -81,6 +82,63 @@ func TestWazeroEngine_Close(t *testing.T) {
 	}
 }
 
+func TestWazeroEngine_FSMountReadlinkRegularFile(t *testing.T) {
+	ctx := context.Background()
+
+	eng, err := NewWazeroEngine(ctx)
+	if err != nil {
+		t.Fatalf("NewWazeroEngine: %v", err)
+	}
+	defer eng.Close(ctx)
+
+	wasmBytes, err := wat.Compile(`(module
+		(import "wasi_snapshot_preview1" "path_readlink"
+			(func $path_readlink (param i32 i32 i32 i32 i32 i32) (result i32)))
+		(memory (export "memory") 1)
+		(data (i32.const 8) "file.txt")
+		(func (export "readlink_errno") (result i32)
+			(call $path_readlink
+				(i32.const 3)
+				(i32.const 8)
+				(i32.const 8)
+				(i32.const 32)
+				(i32.const 64)
+				(i32.const 4))))`)
+	if err != nil {
+		t.Fatalf("compile WAT: %v", err)
+	}
+
+	mod, err := eng.LoadModule(ctx, wasmBytes)
+	if err != nil {
+		t.Fatalf("LoadModule: %v", err)
+	}
+
+	inst, err := mod.InstantiateWithConfig(ctx, &InstanceConfig{
+		Mounts: []Mount{{
+			Guest:    "/data",
+			FS:       fstest.MapFS{"file.txt": &fstest.MapFile{Data: []byte("ok")}},
+			ReadOnly: true,
+		}},
+	})
+	if err != nil {
+		t.Fatalf("InstantiateWithConfig: %v", err)
+	}
+	defer inst.Close(ctx)
+
+	fn := inst.instance.ExportedFunction("readlink_errno")
+	if fn == nil {
+		t.Fatal("readlink_errno function not exported")
+	}
+	results, err := fn.Call(ctx)
+	if err != nil {
+		t.Fatalf("readlink_errno: %v", err)
+	}
+	const wasiErrnoInval = uint64(28)
+	if got := results[0]; got != wasiErrnoInval {
+		t.Fatalf("path_readlink regular file errno = %d, want %d", got, wasiErrnoInval)
+	}
+}
+
 // TestWazeroEngine_HTTPComponentExports verifies HTTP component loading and export resolution.
 func TestWazeroEngine_HTTPComponentExports(t *testing.T) {
 	ctx := context.Background()