Allow users to set the content server port to < 1025 (system ports) witha warning. Fixes #5470 (You can only set the server port with the up and down arrows, not direct entry)

src/calibre/gui2/dialogs/config/__init__.py

@@ -464,6 +464,17 @@ class ConfigDialog(ResizableDialog, Ui_Dialog):
         self.opt_overwrite_author_title_metadata.setChecked(config['overwrite_author_title_metadata'])
         self.opt_enforce_cpu_limit.setChecked(config['enforce_cpu_limit'])
         self.device_detection_button.clicked.connect(self.debug_device_detection)
+        self.port.editingFinished.connect(self.check_port_value)
+
+    def check_port_value(self, *args):
+        port = self.port.value()
+        if port < 1025:
+            warning_dialog(self, _('System port selected'), '<p>'+
+                    _('The value <b>%d</b> you have chosen for the content '
+                        'server port is a system port. You operating '
+                        'system <b>may</b> not allow the server to run on this '
+                        'port. To be safe choose a port number larger than '
+                        '1024.')%port, show=True)
 
     def debug_device_detection(self):
         from calibre.gui2.dialogs.config.device_debug import DebugDevice

src/calibre/gui2/dialogs/config/config.ui

@@ -719,9 +719,6 @@
                </item>
                <item row="0" column="1">
                 <widget class="QSpinBox" name="port">
-                 <property name="minimum">
-                  <number>1025</number>
-                 </property>
                  <property name="maximum">
                   <number>65535</number>
                  </property>