qt network dialog: don't poll Tor socks proxy, but scan on interaction

Polling is introduces spam in Tor logs.
Also, Tor Browser 12.0 apparently has a bug where our polling renders
the socks proxy unusuable after some time.
see https://gitlab.torproject.org/tpo/applications/tor-browser/-/issues/41549

Instead of trying to detect a Tor socks proxy every 10 seconds, we now
run detection when the Qt network dialog gets opened, and also when
the user switches to the "Proxy" tab in the dialog.

fixes https://github.com/spesmilo/electrum/issues/7317

electrum/gui/qt/network_dialog.py

@@ -40,6 +40,7 @@ from electrum import constants, blockchain, util
 from electrum.interface import ServerAddr, PREFERRED_NETWORK_PROTOCOL
 from electrum.network import Network
 from electrum.logging import get_logger
+from electrum.util import detect_tor_socks_proxy
 
 from .util import (Buttons, CloseButton, HelpButton, read_QIcon, char_width_in_lineedit,
                    PasswordLineEdit)
@@ -66,6 +67,11 @@ class NetworkDialog(QDialog, QtEventListener):
         self.register_callbacks()
         self._cleaned_up = False
 
+    def show(self):
+        super().show()
+        if td := self.nlayout.td:
+            td.trigger_rescan()
+
     @qt_event_listener
     def on_event_network_updated(self):
         self.nlayout.update()
@@ -203,10 +209,11 @@ class NetworkChoiceLayout(object):
         self.tor_proxy = None
 
         self.tabs = tabs = QTabWidget()
-        proxy_tab = QWidget()
+        self._proxy_tab = proxy_tab = QWidget()
         blockchain_tab = QWidget()
         tabs.addTab(blockchain_tab, _('Overview'))
         tabs.addTab(proxy_tab, _('Proxy'))
+        tabs.currentChanged.connect(self._on_tab_changed)
 
         fixed_width_hostname = 24 * char_width_in_lineedit()
         fixed_width_port = 6 * char_width_in_lineedit()
@@ -417,6 +424,10 @@ class NetworkChoiceLayout(object):
         net_params = net_params._replace(proxy=proxy)
         self.network.run_from_another_thread(self.network.set_parameters(net_params))
 
+    def _on_tab_changed(self):
+        if self.tabs.currentWidget() is self._proxy_tab:
+            self.td.trigger_rescan()
+
     def suggest_proxy(self, found_proxy):
         if found_proxy is None:
             self.tor_cb.hide()
@@ -457,38 +468,25 @@ class TorDetector(QThread):
 
     def __init__(self):
         QThread.__init__(self)
-        self._stop_event = threading.Event()
+        self._work_to_do_evt = threading.Event()
+        self._stopping = False
 
     def run(self):
-        # Probable ports for Tor to listen at
-        ports = [9050, 9150]
         while True:
-            for p in ports:
-                net_addr = ("127.0.0.1", p)
-                if TorDetector.is_tor_port(net_addr):
-                    self.found_proxy.emit(net_addr)
-                    break
-            else:
-                self.found_proxy.emit(None)
-            stopping = self._stop_event.wait(10)
-            if stopping:
+            # do rescan
+            net_addr = detect_tor_socks_proxy()
+            self.found_proxy.emit(net_addr)
+            # wait until triggered
+            self._work_to_do_evt.wait()
+            self._work_to_do_evt.clear()
+            if self._stopping:
                 return
 
+    def trigger_rescan(self) -> None:
+        self._work_to_do_evt.set()
+
     def stop(self):
-        self._stop_event.set()
+        self._stopping = True
+        self._work_to_do_evt.set()
         self.exit()
         self.wait()
-
-    @staticmethod
-    def is_tor_port(net_addr: Tuple[str, int]) -> bool:
-        try:
-            with socket.socket(socket.AF_INET, socket.SOCK_STREAM) as s:
-                s.settimeout(0.1)
-                s.connect(net_addr)
-                # Tor responds uniquely to HTTP-like requests
-                s.send(b"GET\n")
-                if b"Tor is not an HTTP Proxy" in s.recv(1024):
-                    return True
-        except socket.error:
-            pass
-        return False