feat: add Lstat method to filesystem interface and implementations, with tests

Author: ziflex

pkg/fs/fs.go

@@ -11,6 +11,7 @@ type (
 		Open(path string) (ReadableFile, error)
 		OpenFile(path string, flag int, perm fs.FileMode) (WritableFile, error)
 		Stat(path string) (fs.FileInfo, error)
+		Lstat(path string) (fs.FileInfo, error)
 		Exists(path string) (bool, error)
 	}
 

pkg/fs/fs_disabled.go

@@ -24,6 +24,10 @@ func (n disabledFS) Stat(_ string) (fs.FileInfo, error) {
 	return nil, ErrRootNotConfigured
 }
 
+func (n disabledFS) Lstat(_ string) (fs.FileInfo, error) {
+	return nil, ErrRootNotConfigured
+}
+
 func (n disabledFS) Exists(_ string) (bool, error) {
 	return false, ErrRootNotConfigured
 }

pkg/fs/fs_root.go

@@ -41,6 +41,10 @@ func (r *rootFS) Stat(path string) (fs.FileInfo, error) {
 	return r.root.Stat(path)
 }
 
+func (r *rootFS) Lstat(path string) (fs.FileInfo, error) {
+	return r.root.Lstat(path)
+}
+
 func (r *rootFS) Exists(path string) (bool, error) {
 	_, err := r.root.Stat(path)
 	if err == nil {

pkg/fs/fs_test.go

@@ -0,0 +1,53 @@
+package fs
+
+import (
+	"context"
+	"errors"
+	stdfs "io/fs"
+	"os"
+	"path/filepath"
+	"testing"
+)
+
+func TestRootFSLstatDoesNotFollowFinalSymlink(t *testing.T) {
+	root := t.TempDir()
+	if err := os.WriteFile(filepath.Join(root, "target.txt"), []byte("target"), 0o600); err != nil {
+		t.Fatalf("write target: %v", err)
+	}
+	if err := os.Symlink("target.txt", filepath.Join(root, "link.txt")); err != nil {
+		t.Skipf("symlinks are unavailable: %v", err)
+	}
+
+	filesystem, err := New(WithRoot(root))
+	if err != nil {
+		t.Fatalf("create filesystem: %v", err)
+	}
+
+	metadata, err := ReaderFrom(WithFileSystem(context.Background(), filesystem))
+	if err != nil {
+		t.Fatalf("resolve link metadata: %v", err)
+	}
+
+	info, err := metadata.Lstat("link.txt")
+	if err != nil {
+		t.Fatalf("lstat link: %v", err)
+	}
+	if info.Mode()&stdfs.ModeSymlink == 0 {
+		t.Fatalf("expected symlink metadata, got mode %v", info.Mode())
+	}
+}
+
+func TestDisabledFSLstatPreservesRootDenial(t *testing.T) {
+	filesystem, err := New()
+	if err != nil {
+		t.Fatalf("create disabled filesystem: %v", err)
+	}
+	metadata, err := ReaderFrom(WithFileSystem(context.Background(), filesystem))
+	if err != nil {
+		t.Fatalf("resolve disabled link metadata: %v", err)
+	}
+
+	if _, err := metadata.Lstat("file.txt"); !errors.Is(err, ErrRootNotConfigured) {
+		t.Fatalf("expected ErrRootNotConfigured, got %v", err)
+	}
+}