Refactor IPC exceptions handling.

Also fixes an IPC error when qutebrowser was started twice without delay
between the invocations.

qutebrowser/app.py

@@ -31,6 +31,7 @@ import functools
 import traceback
 import faulthandler
 import json
+import time
 
 from PyQt5.QtWidgets import QApplication, QDialog, QMessageBox
 from PyQt5.QtGui import QDesktopServices, QPixmap, QIcon, QCursor, QWindow
@@ -115,12 +116,18 @@ class Application(QApplication):
                 sys.exit(0)
             log.init.debug("Starting IPC server...")
             ipc.init()
-        except ipc.IPCError as e:
-            text = ('{}\n\nMaybe another instance is running but '
-                    'frozen?'.format(e))
-            msgbox = QMessageBox(QMessageBox.Critical, "Error while "
-                                 "connecting to running instance!", text)
-            msgbox.exec_()
+        except ipc.AddressInUseError as e:
+            # This could be a race condition...
+            log.init.debug("Got AddressInUseError, trying again.")
+            time.sleep(500)
+            sent = ipc.send_to_running_instance(self._args.command)
+            if sent:
+                sys.exit(0)
+            else:
+                ipc.display_error(e)
+                sys.exit(1)
+        except ipc.Error as e:
+            ipc.display_error(e)
             # We didn't really initialize much so far, so we just quit hard.
             sys.exit(1)
 

qutebrowser/misc/ipc.py

@@ -25,7 +25,8 @@ import getpass
 import binascii
 
 from PyQt5.QtCore import pyqtSlot, QObject
-from PyQt5.QtNetwork import QLocalSocket, QLocalServer
+from PyQt5.QtNetwork import QLocalSocket, QLocalServer, QAbstractSocket
+from PyQt5.QtWidgets import QMessageBox
 
 from qutebrowser.utils import log, objreg, usertypes
 
@@ -36,11 +37,40 @@ WRITE_TIMEOUT = 1000
 READ_TIMEOUT = 5000
 
 
-class IPCError(Exception):
+class Error(Exception):
 
     """Exception raised when there was a problem with IPC."""
 
 
+class ListenError(Error):
+
+    """Exception raised when there was a problem with listening to IPC.
+
+    Args:
+        code: The error code.
+        message: The error message.
+    """
+
+    def __init__(self, server):
+        """Constructor.
+
+        Args:
+            server: The QLocalServer which has the error set.
+        """
+        super().__init__()
+        self.code = server.serverError()
+        self.message = server.errorString()
+
+    def __str__(self):
+        return "Error while listening to IPC server: {} (error {})".format(
+            self.message, self.code)
+
+
+class AddressInUseError(ListenError):
+
+    """Emitted when the server address is already in use."""
+
+
 class IPCServer(QObject):
 
     """IPC server to which clients connect to.
@@ -63,9 +93,10 @@ class IPCServer(QObject):
         self._server = QLocalServer(self)
         ok = self._server.listen(SOCKETNAME)
         if not ok:
-            raise IPCError("Error while listening to IPC server: {} "
-                           "(error {})".format(self._server.errorString(),
-                                               self._server.serverError()))
+            if self._server.serverError() == QAbstractSocket.AddressInUseError:
+                raise AddressInUseError(self._server)
+            else:
+                raise ListenError(self._server)
         self._server.newConnection.connect(self.handle_connection)
         self._socket = None
 
@@ -73,8 +104,7 @@ class IPCServer(QObject):
         """Remove an existing server."""
         ok = QLocalServer.removeServer(SOCKETNAME)
         if not ok:
-            raise IPCError("Error while removing server {}!".format(
-                SOCKETNAME))
+            raise Error("Error while removing server {}!".format(SOCKETNAME))
 
     @pyqtSlot(int)
     def on_error(self, error):
@@ -185,13 +215,13 @@ def init():
 
 
 def _socket_error(action, socket):
-    """Raise an IPCError based on an action and a QLocalSocket.
+    """Raise an Error based on an action and a QLocalSocket.
 
     Args:
         action: A string like "writing to running instance".
         socket: A QLocalSocket.
     """
-    raise IPCError("Error while {}: {} (error {})".format(
+    raise Error("Error while {}: {} (error {})".format(
         action, socket.errorString(), socket.error()))
 
 
@@ -235,3 +265,11 @@ def send_to_running_instance(cmdlist):
             log.ipc.debug("No existing instance present (error {})".format(
                 socket.error()))
             return False
+
+
+def display_error(exc):
+    """Display a message box with an IPC error."""
+    text = '{}\n\nMaybe another instance is running but frozen?'.format(exc)
+    msgbox = QMessageBox(QMessageBox.Critical, "Error while connecting to "
+                         "running instance!", text)
+    msgbox.exec_()