Joern MCP Server

Instructions

Implementation Reference

• server_tools.py:36-45 (handler)

  The handler function for the 'get_method_callees' tool. It is decorated with @joern_mcp.tool(), which also serves as the registration mechanism. The function queries the Joern server using joern_remote and processes the response with extract_list.

  @joern_mcp.tool()
  def get_method_callees(method_full_name: str) -> list[str]:
      """Retrieves a list of methods info that are called by the specified method
      
     @param method_full_name: The fully qualified name of the source method(e.g., com.android.nfc.NfcService$6.onReceive:void(android.content.Context,android.content.Intent))
     @return: List of full name, name, signature and id of methods which call the source method
      """
      # responses =  joern_remote(f'cpg.method.fullNameExact("{method_full_name}").head.callee.distinct.map(m => (s"methodFullName=$' + '{m.fullName} methodId=${m.id}L")).l')
      responses = joern_remote(f'get_method_callees("{method_full_name}")')
      return extract_list(responses)  

• server.py:102-104 (registration)

  The exec statement in the generate() function that dynamically loads and executes server_tools.py, thereby registering all tools including 'get_method_callees' via their decorators.

  with open(GENERATED_PY, "r") as f:
      code = f.read()
      exec(compile(code, GENERATED_PY, "exec"))

• server.py:38-70 (helper)

  The joern_remote helper function used by get_method_callees to send queries to the Joern server.

  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:38-45 (helper)

  The extract_list helper function used to parse the list response from Joern queries in get_method_callees.

  def extract_list(input_str):    
      """Extract a list of elements from a string representation of a Scala List.
      
      Parameters:
      input_str -- The input string containing a Scala List representation
      
      Returns:
      A Python list containing the extracted elements with cleaned data