wip: some more drastic refactoring

test/testfs/testfs.go

@@ -0,0 +1,275 @@
+package testfs
+
+import (
+	"errors"
+	"os"
+	"path"
+	"strings"
+)
+
+type Node struct {
+	data  []byte
+	perm  os.FileMode
+	isDir bool
+}
+
+type FS struct {
+	Pwd   string
+	Nodes map[string]*Node
+}
+
+func New() *FS {
+	return &FS{
+		Pwd: "/root",
+		Nodes: map[string]*Node{
+			"/":     {perm: 0o755, isDir: true},
+			"/root": {perm: 0o700, isDir: true},
+		},
+	}
+}
+
+func (fs *FS) MkdirAll(name string, perm os.FileMode) error {
+	if !path.IsAbs(name) && name != "" {
+		name = path.Join(fs.Pwd, name)
+	}
+
+	dirs := []string{name}
+	for d := path.Dir(name); d != "/"; d = path.Dir(d) {
+		dirs = append(dirs, d)
+	}
+	dirs = append(dirs, "/")
+
+	for i := len(dirs) - 1; i >= 0; i-- {
+		dir := dirs[i]
+		parent := path.Dir(dir)
+
+		if info, ok := fs.Nodes[dir]; ok {
+			if !info.isDir {
+				return &os.PathError{
+					Op:   "mkdir",
+					Path: dir,
+					Err:  errors.New("not a directory"),
+				}
+			}
+
+			continue
+		}
+
+		parentInfo, ok := fs.Nodes[parent]
+		if !ok {
+			return &os.PathError{
+				Op:   "mkdir",
+				Path: parent,
+				Err:  errors.New("no such file or directory"),
+			}
+		}
+		if !parentInfo.isDir {
+			return &os.PathError{
+				Op:   "mkdir",
+				Path: parent,
+				Err:  errors.New("not a directory"),
+			}
+		}
+		// Ensure all parent directories have execute permissions, and direct
+		// parent also has write permission.
+		if parentInfo.perm&0o100 == 0 || i == 1 && parentInfo.perm&0o200 == 0 {
+			return &os.PathError{
+				Op:   "mkdir",
+				Path: dir,
+				Err:  errors.New("permission denied"),
+			}
+		}
+
+		fs.Nodes[dir] = &Node{perm: perm, isDir: true}
+	}
+
+	return nil
+}
+
+func (fs *FS) ReadFile(name string) ([]byte, error) {
+	if !path.IsAbs(name) && name != "" {
+		name = path.Join(fs.Pwd, name)
+	}
+
+	_, err := fs.checkParents(name, false)
+	if err != nil {
+		return nil, err
+	}
+
+	info, ok := fs.Nodes[name]
+	if !ok {
+		return nil, &os.PathError{
+			Op:   "open",
+			Path: name,
+			Err:  errors.New("no such file or directory"),
+		}
+	}
+	if info.isDir {
+		return nil, &os.PathError{
+			Op:   "open",
+			Path: name,
+			Err:  errors.New("is a directory"),
+		}
+	}
+	if info.perm&0o400 == 0 {
+		return nil, &os.PathError{
+			Op:   "open",
+			Path: name,
+			Err:  errors.New("permission denied"),
+		}
+	}
+
+	return info.data, nil
+}
+
+func (fs *FS) WriteFile(name string, data []byte, perm os.FileMode) error {
+	if !path.IsAbs(name) && name != "" {
+		name = path.Join(fs.Pwd, name)
+	}
+
+	parent, err := fs.checkParents(name, true)
+	if err != nil {
+		return err
+	}
+
+	info, ok := fs.Nodes[name]
+	if ok {
+		if info.isDir {
+			return &os.PathError{
+				Op:   "open",
+				Path: name,
+				Err:  errors.New("is a directory"),
+			}
+		}
+	}
+	// Return error if file exists and has no write permission, or if the file
+	// does not exist and the direct parent has no write permission.
+	if ok && info.perm&0o200 == 0 || !ok && parent.perm&0o200 == 0 {
+		return &os.PathError{
+			Op:   "open",
+			Path: name,
+			Err:  errors.New("permission denied"),
+		}
+	}
+
+	fs.Nodes[name] = &Node{data: data, perm: perm}
+
+	return nil
+}
+
+func (fs *FS) Remove(name string) error {
+	if !path.IsAbs(name) && name != "" {
+		name = path.Join(fs.Pwd, name)
+	}
+
+	parent, err := fs.checkParents(name, false)
+	if err != nil {
+		return err
+	}
+
+	if parent != nil && parent.perm&0o200 == 0 {
+		return &os.PathError{
+			Op:   "remove",
+			Path: name,
+			Err:  errors.New("permission denied"),
+		}
+	}
+
+	info, ok := fs.Nodes[name]
+	if !ok {
+		return &os.PathError{
+			Op:   "remove",
+			Path: name,
+			Err:  errors.New("no such file or directory"),
+		}
+	}
+	if info.perm&0o200 == 0 {
+		return &os.PathError{
+			Op:   "remove",
+			Path: name,
+			Err:  errors.New("permission denied"),
+		}
+	}
+	if info.isDir {
+		for p := range fs.Nodes {
+			if strings.HasPrefix(p, name) && p != name {
+				return &os.PathError{
+					Op:   "remove",
+					Path: name,
+					Err:  errors.New("directory not empty"),
+				}
+			}
+		}
+	}
+
+	delete(fs.Nodes, name)
+
+	return nil
+}
+
+func (fs *FS) Exists(name string) bool {
+	if !path.IsAbs(name) && name != "" {
+		name = path.Join(fs.Pwd, name)
+	}
+
+	_, ok := fs.Nodes[name]
+
+	return ok
+}
+
+func (fs *FS) FileMode(name string) (os.FileMode, error) {
+	if !path.IsAbs(name) && name != "" {
+		name = path.Join(fs.Pwd, name)
+	}
+
+	if info, ok := fs.Nodes[name]; ok {
+		return info.perm, nil
+	}
+
+	return 0, &os.PathError{
+		Op:   "open",
+		Path: name,
+		Err:  os.ErrNotExist,
+	}
+}
+
+func (fs *FS) checkParents(absPath string, noExistError bool) (*Node, error) {
+	var parents []string
+	for d := path.Dir(absPath); d != "/"; d = path.Dir(d) {
+		parents = append(parents, d)
+	}
+	parents = append(parents, "/")
+	var directParent *Node
+
+	for i := 0; i < len(parents); i++ {
+		dir := parents[i]
+		info, ok := fs.Nodes[dir]
+		if !ok && noExistError {
+			return nil, &os.PathError{
+				Op:   "open",
+				Path: dir,
+				Err:  errors.New("no such file or directory"),
+			}
+		}
+		if info != nil && !info.isDir {
+			return nil, &os.PathError{
+				Op:   "open",
+				Path: dir,
+				Err:  errors.New("not a directory"),
+			}
+		}
+		// Ensure all parent directories have execute permissions.
+		if info != nil && info.perm&0o100 == 0 {
+			return nil, &os.PathError{
+				Op:   "open",
+				Path: dir,
+				Err:  errors.New("permission denied"),
+			}
+		}
+		if i == 0 {
+			directParent = info
+		}
+	}
+
+	return directParent, nil
+}