code: func (ns *Namespace) Config(path interface{}) (image.Config, error) {
  	filename, err := cast.ToStringE(path)
  	if err != nil {
  		return image.Config{}, err
  	}
  
  	if filename == "" {
  		return image.Config{}, errors.New("config needs a filename")
  	}
  
  	// Check cache for image config.
  	ns.cacheMu.RLock()
  	config, ok := ns.cache[filename]
  	ns.cacheMu.RUnlock()
  
  	if ok {
  		return config, nil
  	}
  
  	f, err := ns.deps.Fs.WorkingDir.Open(filename)
  	if err != nil {
  		return image.Config{}, err
  	}
  	defer f.Close()
  
  	config, _, err = image.DecodeConfig(f)
  	if err != nil {
  		return config, err
  	}
  
  	ns.cacheMu.Lock()
  	ns.cache[filename] = config
  	ns.cacheMu.Unlock()
  
  	return config, nil
  }
docs: // Config returns the image.Config for the specified path relative to the
  // working directory.