gui: Fix proxy setting options dialog crash

This fixes a crash bug when opening the options dialog.

- Check the return value of split() to avoid segmentation faults due to
  out of bounds when the user manages to enter invalid proxy settings.
  This is reported resonably often.

- Move the default proxy/port to a constant instead of hardcoding magic
  values.

- Factor out some common code.

- Revert #11448 because this proves a more robust replacement, it is no
  longer necessary and didn't generally solve the issue.

No attempt is made to do full sanity checking on the proxy, so it can
still be rejected by the core with an InitError message.

3 files changed, 61 insertions, 53 deletions

diff --git a/src/qt/optionsdialog.cpp b/src/qt/optionsdialog.cpp
index d7aa8bc38b..a0f78d5ead 100644
--- a/src/qt/optionsdialog.cpp
+++ b/src/qt/optionsdialog.cpp
@@ -338,7 +338,7 @@ QValidator::State ProxyAddressValidator::validate(QString &input, int &pos) cons
 {
     Q_UNUSED(pos);
     // Validate the proxy
-    CService serv(LookupNumeric(input.toStdString().c_str(), 9050));
+    CService serv(LookupNumeric(input.toStdString().c_str(), DEFAULT_GUI_PROXY_PORT));
     proxyType addrProxy = proxyType(serv, true);
     if (addrProxy.IsValid())
         return QValidator::Acceptable;
diff --git a/src/qt/optionsmodel.cpp b/src/qt/optionsmodel.cpp
index a0645d9a74..52b4d4e42e 100644
--- a/src/qt/optionsmodel.cpp
+++ b/src/qt/optionsmodel.cpp
@@ -28,6 +28,8 @@
 #include <QSettings>
 #include <QStringList>
 
+const char *DEFAULT_GUI_PROXY_HOST = "127.0.0.1";
+
 OptionsModel::OptionsModel(QObject *parent, bool resetSettings) :
     QAbstractListModel(parent)
 {
@@ -124,8 +126,8 @@ void OptionsModel::Init(bool resetSettings)
 
     if (!settings.contains("fUseProxy"))
         settings.setValue("fUseProxy", false);
-    if (!settings.contains("addrProxy") || !settings.value("addrProxy").toString().contains(':'))
-        settings.setValue("addrProxy", "127.0.0.1:9050");
+    if (!settings.contains("addrProxy"))
+        settings.setValue("addrProxy", QString("%1:%2").arg(DEFAULT_GUI_PROXY_HOST, DEFAULT_GUI_PROXY_PORT));
     // Only try to set -proxy, if user has enabled fUseProxy
     if (settings.value("fUseProxy").toBool() && !gArgs.SoftSetArg("-proxy", settings.value("addrProxy").toString().toStdString()))
         addOverriddenOption("-proxy");
@@ -134,8 +136,8 @@ void OptionsModel::Init(bool resetSettings)
 
     if (!settings.contains("fUseSeparateProxyTor"))
         settings.setValue("fUseSeparateProxyTor", false);
-    if (!settings.contains("addrSeparateProxyTor") || !settings.value("addrSeparateProxyTor").toString().contains(':'))
-        settings.setValue("addrSeparateProxyTor", "127.0.0.1:9050");
+    if (!settings.contains("addrSeparateProxyTor"))
+        settings.setValue("addrSeparateProxyTor", QString("%1:%2").arg(DEFAULT_GUI_PROXY_HOST, DEFAULT_GUI_PROXY_PORT));
     // Only try to set -onion, if user has enabled fUseSeparateProxyTor
     if (settings.value("fUseSeparateProxyTor").toBool() && !gArgs.SoftSetArg("-onion", settings.value("addrSeparateProxyTor").toString().toStdString()))
         addOverriddenOption("-onion");
@@ -200,6 +202,33 @@ int OptionsModel::rowCount(const QModelIndex & parent) const
     return OptionIDRowCount;
 }
 
+struct ProxySetting {
+    bool is_set;
+    QString ip;
+    QString port;
+};
+
+static ProxySetting GetProxySetting(QSettings &settings, const QString &name)
+{
+    static const ProxySetting default_val = {false, DEFAULT_GUI_PROXY_HOST, QString("%1").arg(DEFAULT_GUI_PROXY_PORT)};
+    // Handle the case that the setting is not set at all
+    if (!settings.contains(name)) {
+        return default_val;
+    }
+    // contains IP at index 0 and port at index 1
+    QStringList ip_port = settings.value(name).toString().split(":", QString::SkipEmptyParts);
+    if (ip_port.size() == 2) {
+        return {true, ip_port.at(0), ip_port.at(1)};
+    } else { // Invalid: return default
+        return default_val;
+    }
+}
+
+static void SetProxySetting(QSettings &settings, const QString &name, const ProxySetting &ip_port)
+{
+    settings.setValue(name, ip_port.ip + ":" + ip_port.port);
+}
+
 // read QSettings values and return them
 QVariant OptionsModel::data(const QModelIndex & index, int role) const
 {
@@ -226,30 +255,18 @@ QVariant OptionsModel::data(const QModelIndex & index, int role) const
         // default proxy
         case ProxyUse:
             return settings.value("fUseProxy", false);
-        case ProxyIP: {
-            // contains IP at index 0 and port at index 1
-            QStringList strlIpPort = settings.value("addrProxy").toString().split(":", QString::SkipEmptyParts);
-            return strlIpPort.at(0);
-        }
-        case ProxyPort: {
-            // contains IP at index 0 and port at index 1
-            QStringList strlIpPort = settings.value("addrProxy").toString().split(":", QString::SkipEmptyParts);
-            return strlIpPort.at(1);
-        }
+        case ProxyIP:
+            return GetProxySetting(settings, "addrProxy").ip;
+        case ProxyPort:
+            return GetProxySetting(settings, "addrProxy").port;
 
         // separate Tor proxy
         case ProxyUseTor:
             return settings.value("fUseSeparateProxyTor", false);
-        case ProxyIPTor: {
-            // contains IP at index 0 and port at index 1
-            QStringList strlIpPort = settings.value("addrSeparateProxyTor").toString().split(":", QString::SkipEmptyParts);
-            return strlIpPort.at(0);
-        }
-        case ProxyPortTor: {
-            // contains IP at index 0 and port at index 1
-            QStringList strlIpPort = settings.value("addrSeparateProxyTor").toString().split(":", QString::SkipEmptyParts);
-            return strlIpPort.at(1);
-        }
+        case ProxyIPTor:
+            return GetProxySetting(settings, "addrSeparateProxyTor").ip;
+        case ProxyPortTor:
+            return GetProxySetting(settings, "addrSeparateProxyTor").port;
 
 #ifdef ENABLE_WALLET
         case SpendZeroConfChange:
@@ -314,25 +331,19 @@ bool OptionsModel::setData(const QModelIndex & index, const QVariant & value, in
             }
             break;
         case ProxyIP: {
-            // contains current IP at index 0 and current port at index 1
-            QStringList strlIpPort = settings.value("addrProxy").toString().split(":", QString::SkipEmptyParts);
-            // if that key doesn't exist or has a changed IP
-            if (!settings.contains("addrProxy") || strlIpPort.at(0) != value.toString()) {
-                // construct new value from new IP and current port
-                QString strNewValue = value.toString() + ":" + strlIpPort.at(1);
-                settings.setValue("addrProxy", strNewValue);
+            auto ip_port = GetProxySetting(settings, "addrProxy");
+            if (!ip_port.is_set || ip_port.ip != value.toString()) {
+                ip_port.ip = value.toString();
+                SetProxySetting(settings, "addrProxy", ip_port);
                 setRestartRequired(true);
             }
         }
         break;
         case ProxyPort: {
-            // contains current IP at index 0 and current port at index 1
-            QStringList strlIpPort = settings.value("addrProxy").toString().split(":", QString::SkipEmptyParts);
-            // if that key doesn't exist or has a changed port
-            if (!settings.contains("addrProxy") || strlIpPort.at(1) != value.toString()) {
-                // construct new value from current IP and new port
-                QString strNewValue = strlIpPort.at(0) + ":" + value.toString();
-                settings.setValue("addrProxy", strNewValue);
+            auto ip_port = GetProxySetting(settings, "addrProxy");
+            if (!ip_port.is_set || ip_port.port != value.toString()) {
+                ip_port.port = value.toString();
+                SetProxySetting(settings, "addrProxy", ip_port);
                 setRestartRequired(true);
             }
         }
@@ -346,25 +357,19 @@ bool OptionsModel::setData(const QModelIndex & index, const QVariant & value, in
             }
             break;
         case ProxyIPTor: {
-            // contains current IP at index 0 and current port at index 1
-            QStringList strlIpPort = settings.value("addrSeparateProxyTor").toString().split(":", QString::SkipEmptyParts);
-            // if that key doesn't exist or has a changed IP
-            if (!settings.contains("addrSeparateProxyTor") || strlIpPort.at(0) != value.toString()) {
-                // construct new value from new IP and current port
-                QString strNewValue = value.toString() + ":" + strlIpPort.at(1);
-                settings.setValue("addrSeparateProxyTor", strNewValue);
+            auto ip_port = GetProxySetting(settings, "addrSeparateProxyTor");
+            if (!ip_port.is_set || ip_port.ip != value.toString()) {
+                ip_port.ip = value.toString();
+                SetProxySetting(settings, "addrSeparateProxyTor", ip_port);
                 setRestartRequired(true);
             }
         }
         break;
         case ProxyPortTor: {
-            // contains current IP at index 0 and current port at index 1
-            QStringList strlIpPort = settings.value("addrSeparateProxyTor").toString().split(":", QString::SkipEmptyParts);
-            // if that key doesn't exist or has a changed port
-            if (!settings.contains("addrSeparateProxyTor") || strlIpPort.at(1) != value.toString()) {
-                // construct new value from current IP and new port
-                QString strNewValue = strlIpPort.at(0) + ":" + value.toString();
-                settings.setValue("addrSeparateProxyTor", strNewValue);
+            auto ip_port = GetProxySetting(settings, "addrSeparateProxyTor");
+            if (!ip_port.is_set || ip_port.port != value.toString()) {
+                ip_port.port = value.toString();
+                SetProxySetting(settings, "addrSeparateProxyTor", ip_port);
                 setRestartRequired(true);
             }
         }
diff --git a/src/qt/optionsmodel.h b/src/qt/optionsmodel.h
index b6e8fdef68..f8782dd204 100644
--- a/src/qt/optionsmodel.h
+++ b/src/qt/optionsmodel.h
@@ -13,6 +13,9 @@ QT_BEGIN_NAMESPACE
 class QNetworkProxy;
 QT_END_NAMESPACE
 
+extern const char *DEFAULT_GUI_PROXY_HOST;
+static constexpr unsigned short DEFAULT_GUI_PROXY_PORT = 9050;
+
 /** Interface from Qt to configuration data structure for Bitcoin client.
    To Qt, the options are presented as a list with the different options
    laid out vertically.