Alternative option: abstract namespace

securedrop_client/app.py

@@ -21,10 +21,10 @@
 import os
 import signal
 import sys
+import socket
 from sqlalchemy.orm import sessionmaker
 from PyQt5.QtWidgets import QApplication, QMessageBox
 from PyQt5.QtCore import Qt, QTimer
-from PyQt5.QtNetwork import QLocalServer, QLocalSocket
 from logging.handlers import TimedRotatingFileHandler
 from securedrop_client import __version__
 from securedrop_client.logic import Client
@@ -73,29 +73,18 @@ def configure_logging():
 
 
 def prevent_second_instance(app: QApplication) -> None:
-    IDENTIFIER = app.applicationName() + str(os.getuid())
-
-    def already_running() -> bool:
-        TIMEOUT = 3000
-        socket = QLocalSocket(app)
-        socket.connectToServer(IDENTIFIER, socket.NotOpen)
-        if socket.waitForConnected(TIMEOUT):
-            socket.disconnectFromServer()
-            return True
-        else:
-            return False
-
-    def setup_instance_listener() -> None:
-        QLocalServer.removeServer(IDENTIFIER)
-        app.instance_listener = QLocalServer(app)
-        app.instance_listener.listen(IDENTIFIER)
-
-    if already_running():
-        error = QMessageBox()
-        error.setText(app.applicationName() + ' is already running.')
-        sys.exit(error.exec())
-    else:
-        setup_instance_listener()
+    # Null byte triggers abstract namespace
+    IDENTIFIER = '\0' + app.applicationName() + str(os.getuid())
+    ALREADY_BOUND_ERRNO = 98
+
+    app.instance_binding = socket.socket(socket.AF_UNIX, socket.SOCK_DGRAM)
+    try:
+        app.instance_binding.bind(IDENTIFIER)
+    except OSError as e:
+        if e.errno == ALREADY_BOUND_ERRNO:
+            error_dialog = QMessageBox()
+            error_dialog.setText(app.applicationName() + ' is already running.')
+            sys.exit(error_dialog.exec())
 
 
 def run():