Add a framework for easily and securely using remote control from the main function of a custom kitten

tools/cmd/at/main.go

@@ -326,6 +326,17 @@ func get_password(password string, password_file string, password_env string, us
 					ttyf.Close()
 				}
 			}
+		} else if strings.HasPrefix(password_file, "fd:") {
+			var fd int
+			if fd, err = strconv.Atoi(password_file[3:]); err == nil {
+				f := os.NewFile(uintptr(fd), password_file)
+				var q []byte
+				if q, err = io.ReadAll(f); err == nil {
+					ans.is_set = true
+					ans.val = string(q)
+				}
+				f.Close()
+			}
 		} else {
 			var q []byte
 			q, err = os.ReadFile(password_file)

tools/cmd/at/socket_io.go

@@ -170,7 +170,7 @@ func do_socket_io(io_data *rc_io_data) (serialized_response []byte, err error) {
 		f := os.NewFile(uintptr(fd), "fd:"+global_options.to_address)
 		conn, err = net.FileConn(f)
 		if err != nil {
-			return nil, err
+			return nil, fmt.Errorf("Failed to open a socket for the remote control file descriptor: %d with error: %w", fd, err)
 		}
 		defer f.Close()
 	} else {