input: def feature_extraction(input_str: str) -> dict:
      """ Extracts specific features from a JSON string. 
      >>> feature_extraction('{"id": 111, "title": "This is a sample title", "body": "This is a sample body text"}')
      {'id': 111, 'title': 'This is a sample title', 'body_len': 31}
      >>> feature_extraction('{"id": 222, "title": "Another title", "body": "Short body"}')
      {'id': 222, 'title': 'Another title', 'body_len': 10}
      """
output:     import json
      data = json.loads(input_str)
      result = {
          'id': data['id'],
          'title': data['title'],
          'body_len': len(data['body'])
      }
      return result