Joern MCP Server

Instructions

@param class_full_name: The fully qualified name of the class
@param method_name: The name of the method
@return: List of full name, name, signature and id of methods in the class

Implementation Reference

• server_tools.py:87-96 (handler)

  Handler function for 'get_method_code_by_id' tool. Decorated with @joern_mcp.tool() for automatic registration in FastMCP. Queries Joern server remotely using joern_remote and parses response with extract_value to return method source code by ID.

  @joern_mcp.tool()
  def get_method_code_by_id(method_id:str) -> str:
      """Get the code of a method by its class full name and method name
    
      @param class_full_name: The fully qualified name of the class
      @param method_name: The name of the method
      @return: List of full name, name, signature and id of methods in the class
      """
      response =  joern_remote(f'get_method_code_by_id("{method_id}")')
      return extract_value(response)

• server.py:38-70 (helper)

  Core helper function joern_remote that sends HTTP POST requests to the Joern server endpoint with the CPG query, authenticates, handles timeouts, cleans ANSI sequences from stdout response.

  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)

  Utility function extract_value that parses Joern query responses to extract the relevant value (code, ID, name, etc.) based on patterns like triple quotes for code blocks or quoted strings.

  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

• server.py:94-106 (registration)

  Dynamic registration mechanism: server.py executes the code in server_tools.py via exec(), which runs all @joern_mcp.tool() decorators to register tools including 'get_method_code_by_id' to the FastMCP instance.

  SCRIPT_DIR = os.path.dirname(os.path.realpath(__file__))
  GENERATED_PY = os.path.join(SCRIPT_DIR, "server_tools.py")
  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()