Add ability to scan snaps (as a source) (#3929)

internal/file/squashfs.go

@@ -0,0 +1,89 @@
+package file
+
+import (
+	"errors"
+	"io/fs"
+	"os"
+	"path/filepath"
+
+	"github.com/diskfs/go-diskfs/filesystem"
+)
+
+type WalkDiskDirFunc func(fsys filesystem.FileSystem, path string, d os.FileInfo, err error) error
+
+// WalkDiskDir walks the file tree within the go-diskfs filesystem at root, calling fn for each file or directory in the tree, including root.
+// This is meant to mimic the behavior of fs.WalkDir in the standard library.
+func WalkDiskDir(fsys filesystem.FileSystem, root string, fn WalkDiskDirFunc) error {
+	infos, err := fsys.ReadDir(root)
+
+	if err != nil {
+		return err
+	}
+
+	if len(infos) == 0 {
+		return nil
+	}
+
+	for _, info := range infos {
+		p := filepath.Join(root, info.Name())
+		err = walkDiskDir(fsys, p, info, fn)
+		if err != nil {
+			if errors.Is(err, fs.SkipDir) {
+				continue
+			}
+			if errors.Is(err, fs.SkipAll) {
+				return nil
+			}
+			return err
+		}
+	}
+
+	return err
+}
+
+func walkDiskDir(fsys filesystem.FileSystem, name string, d os.FileInfo, walkDirFn WalkDiskDirFunc) error {
+	if err := walkDirFn(fsys, name, d, nil); err != nil {
+		if errors.Is(err, fs.SkipDir) && (d == nil || d.IsDir()) {
+			return nil
+		}
+		return err
+	}
+
+	isDir := d != nil && d.IsDir()
+	if d == nil {
+		_, err := fsys.ReadDir(name)
+		if err != nil {
+			return nil
+		}
+		isDir = true
+	}
+
+	if !isDir {
+		return nil
+	}
+
+	dirs, err := fsys.ReadDir(name)
+	if err != nil {
+		err = walkDirFn(fsys, name, d, err)
+		if err != nil {
+			if errors.Is(err, fs.SkipDir) {
+				return nil
+			}
+			return err
+		}
+	}
+
+	for _, d1 := range dirs {
+		name1 := filepath.Join(name, d1.Name())
+		if err := walkDiskDir(fsys, name1, d1, walkDirFn); err != nil {
+			if errors.Is(err, fs.SkipDir) {
+				break
+			}
+			if errors.Is(err, fs.SkipAll) {
+				return err
+			}
+			return err
+		}
+	}
+	return nil
+}