| package symlink |
| |
| import ( |
| "fmt" |
| "os" |
| "path" |
| "path/filepath" |
| "strings" |
| ) |
| |
| const maxLoopCounter = 100 |
| |
| // FollowSymlink will follow an existing link and scope it to the root |
| // path provided. |
| func FollowSymlinkInScope(link, root string) (string, error) { |
| prev := "/" |
| |
| root, err := filepath.Abs(root) |
| if err != nil { |
| return "", err |
| } |
| |
| link, err = filepath.Abs(link) |
| if err != nil { |
| return "", err |
| } |
| |
| if !strings.HasPrefix(filepath.Dir(link), root) { |
| return "", fmt.Errorf("%s is not within %s", link, root) |
| } |
| |
| for _, p := range strings.Split(link, "/") { |
| prev = filepath.Join(prev, p) |
| prev = filepath.Clean(prev) |
| |
| loopCounter := 0 |
| for { |
| loopCounter++ |
| |
| if loopCounter >= maxLoopCounter { |
| return "", fmt.Errorf("loopCounter reached MAX: %v", loopCounter) |
| } |
| |
| if !strings.HasPrefix(prev, root) { |
| // Don't resolve symlinks outside of root. For example, |
| // we don't have to check /home in the below. |
| // |
| // /home -> usr/home |
| // FollowSymlinkInScope("/home/bob/foo/bar", "/home/bob/foo") |
| break |
| } |
| |
| stat, err := os.Lstat(prev) |
| if err != nil { |
| if os.IsNotExist(err) { |
| break |
| } |
| return "", err |
| } |
| if stat.Mode()&os.ModeSymlink == os.ModeSymlink { |
| dest, err := os.Readlink(prev) |
| if err != nil { |
| return "", err |
| } |
| |
| if path.IsAbs(dest) { |
| prev = filepath.Join(root, dest) |
| } else { |
| prev, _ = filepath.Abs(prev) |
| |
| if prev = filepath.Clean(filepath.Join(filepath.Dir(prev), dest)); len(prev) < len(root) { |
| prev = filepath.Join(root, filepath.Base(dest)) |
| } |
| } |
| } else { |
| break |
| } |
| } |
| } |
| return prev, nil |
| } |