Joern MCP Server

Instructions

@param id: The unique identifier of the method, the id is a Long int string, like '111669149702L'
@return: The fully qualified name of the method (e.g., com.android.nfc.NfcService$6.onReceive:void(android.content.Context,android.content.Intent))

Implementation Reference

• server_tools.py:98-106 (handler)

  The handler function for the get_method_full_name_by_id tool. It uses the @joern_mcp.tool() decorator for automatic registration and schema inference from type hints and docstring. The logic queries the Joern server remotely and extracts the result.

  @joern_mcp.tool()
  def get_method_full_name_by_id(method_id:str) -> str:
      """Retrieves the fully qualified name of a method by its ID
      
      @param id: The unique identifier of the method, the id is a Long int string, like '111669149702L'
      @return: The fully qualified name of the method (e.g., com.android.nfc.NfcService$6.onReceive:void(android.content.Context,android.content.Intent))
      """
      response = joern_remote(f'get_method_full_name_by_id("{method_id}")')
      return extract_value(response)

• server.py:32-32 (registration)

  Creation of the FastMCP server instance named 'joern_mcp' which is used to register all tools via decorators.

  joern_mcp = FastMCP("joern-mcp", log_level=log_level)

• server.py:96-106 (registration)

  Dynamic registration of tools from server_tools.py by executing its code, which applies the @joern_mcp.tool() decorators to register get_method_full_name_by_id and others.

  def generate():
      """Generate and execute additional server tools from server_tools.py file.
      
      This function reads the content of server_tools.py and executes it to add
      more functionality to the server.
      """
      with open(GENERATED_PY, "r") as f:
          code = f.read()
          exec(compile(code, GENERATED_PY, "exec"))
  
  generate()

• server.py:38-70 (helper)

  Helper function to send HTTP POST requests to the Joern server with the query and return cleaned stdout response, used by the tool handler.

  def joern_remote(query):
      """
      Execute remote query and return results
      
      Parameters:
      query -- The query string to execute
      
      Returns:
      Returns the server response stdout content on success
      Returns None on failure, error message will be output to stderr
      """
      data = {"query": query}
      headers = {'Content-Type': 'application/json'}
  
      try:
          response = requests.post(
              f'http://{server_endpoint}/query-sync',
              data=json.dumps(data),
              headers=headers,
              auth=basic_auth,
              timeout=timeout
          )
          response.raise_for_status()  
          
          result = response.json()
          return remove_ansi_escape_sequences(result.get('stdout', ''))
          
      except requests.exceptions.RequestException as e:
          sys.stderr.write(f"Request Error: {str(e)}\n")
      except json.JSONDecodeError:
          sys.stderr.write("Error: Invalid JSON response\n")
      
      return None

• common_tools.py:111-133 (helper)

  Helper utility to parse and extract the value from Joern query responses based on patterns, used in the tool handler to process the response.

  def extract_value(input_str: str) -> str:
      """Extract value from a string based on its pattern.
      
      This function automatically selects the appropriate extraction method based on
      the input string format:
      * If contains 'Long =', uses extract_long_value
      * If contains triple quotes, uses extract_code_between_triple_quotes
      * If contains single quotes, uses extract_quoted_string
      
      Args:
          input_str (str): Input string containing a value to extract
          
      Returns:
          str: Extracted value based on the detected pattern
      """
      if 'Long =' in input_str:
          return extract_long_value(input_str)
      elif 'String = """' in input_str:
          return extract_code_between_triple_quotes(input_str)
      elif 'String = "' in input_str:
          return extract_quoted_string(input_str)
      else:
          return input_str