qml: validate server address in ServerConfig

Same as Qt, validate the server address the user enters and prevent the
user from continuing in the wizard or clicking 'Ok' in the ServerConfig
if the entered address is clearly invalid.

electrum/gui/qml/components/ServerConfigDialog.qml

@@ -39,6 +39,7 @@ ElDialog {
         FlatButton {
             Layout.fillWidth: true
             text: qsTr('Ok')
+            enabled: serverconfig.addressValid
             icon.source: '../../icons/confirmed.png'
             onClicked: {
                 let auto_connect = serverconfig.serverConnectMode == ServerConnectModeComboBox.Mode.Autoconnect

electrum/gui/qml/components/controls/ServerConfig.qml

@@ -12,6 +12,7 @@ Item {
     property bool showAutoselectServer: true
     property alias address: address_tf.text
     property alias serverConnectMode: server_connect_mode_cb.currentValue
+    property alias addressValid: address_tf.valid
 
     implicitHeight: rootLayout.height
 
@@ -28,6 +29,11 @@ Item {
 
             ServerConnectModeComboBox {
                 id: server_connect_mode_cb
+                onCurrentValueChanged: {
+                    if (currentValue == ServerConnectModeComboBox.Mode.Autoconnect) {
+                        address_tf.text = ""
+                    }
+                }
             }
 
             Item {
@@ -63,6 +69,26 @@ Item {
                 enabled: server_connect_mode_cb.currentValue != ServerConnectModeComboBox.Mode.Autoconnect
                 width: parent.width
                 inputMethodHints: Qt.ImhNoPredictiveText
+
+                property bool valid: true
+
+                function validate() {
+                    if (!enabled) {
+                        valid = true
+                        return
+                    }
+                    valid = Network.isValidServerAddress(address_tf.text)
+                }
+
+                onTextChanged: validate()
+                onEnabledChanged: validate()
+
+                Rectangle {
+                    anchors.fill: parent
+                    color: "red"
+                    opacity: 0.2
+                    visible: !parent.valid
+                }
             }
         }
 

electrum/gui/qml/components/wizard/WCServerConfig.qml

@@ -5,7 +5,7 @@ import QtQuick.Controls
 import "../controls"
 
 WizardComponent {
-    valid: true
+    valid: sc.addressValid
     last: true
     title: qsTr('Server')
 

electrum/gui/qml/qenetwork.py

@@ -206,6 +206,10 @@ class QENetwork(QObject, QtEventListener):
     def server(self):
         return self._server
 
+    @pyqtSlot(str, result=bool)
+    def isValidServerAddress(self, server: str) -> bool:
+        return ServerAddr.from_str_with_inference(server) is not None
+
     @pyqtSlot(str, bool, bool)
     def setServerParameters(self, server_str: str, auto_connect: bool, one_server: bool):
         net_params = self.network.get_parameters()