code: func (d *driver) Writer(context context.Context, path string, append bool) (storagedriver.FileWriter, error) {
  	writer := &writer{
  		client: d.client,
  		bucket: d.bucket,
  		name:   d.pathToKey(path),
  		buffer: make([]byte, d.chunkSize),
  	}
  
  	if append {
  		err := writer.init(path)
  		if err != nil {
  			return nil, err
  		}
  	}
  	return writer, nil
  }
docs: // Writer returns a FileWriter which will store the content written to it
  // at the location designated by "path" after the call to Commit.