use AssocQueryString instead of directly querying the registry

CHANGELOG.md

@@ -47,6 +47,7 @@
 - Dev: Added CMake Install Support on Windows. (#4300)
 - Dev: Changed conan generator to [`CMakeDeps`](https://docs.conan.io/en/latest/reference/conanfile/tools/cmake/cmakedeps.html) and [`CMakeToolchain`](https://docs.conan.io/en/latest/reference/conanfile/tools/cmake/cmaketoolchain.html). See PR for migration notes. (#4335)
 - Dev: Refactored 7TV EventAPI implementation. (#4342)
+- Dev: Don't rely on undocumented registry keys to find the default browser on Windows. (#4362)
 
 ## 2.4.0
 

src/util/IncognitoBrowser.cpp

@@ -1,15 +1,17 @@
 #include "util/IncognitoBrowser.hpp"
+#ifdef USEWINSDK
+#    include "util/WindowsHelper.hpp"
+#endif
 
 #include <QProcess>
 #include <QRegularExpression>
-#include <QSettings>
 #include <QVariant>
 
 namespace {
 
 using namespace chatterino;
 
-#ifdef Q_OS_WIN
+#ifdef USEWINSDK
 QString injectPrivateSwitch(QString command)
 {
     // list of command line switches to turn on private browsing in browsers
@@ -47,23 +49,27 @@ QString injectPrivateSwitch(QString command)
 
 QString getCommand()
 {
-    // get default browser prog id
-    auto browserId = QSettings("HKEY_CURRENT_"
-                               "USER\\Software\\Microsoft\\Windows\\Shell\\"
-                               "Associations\\UrlAssociatio"
-                               "ns\\http\\UserChoice",
-                               QSettings::NativeFormat)
-                         .value("Progid")
-                         .toString();
-
-    // get default browser start command
-    auto command =
-        QSettings("HKEY_CLASSES_ROOT\\" + browserId + "\\shell\\open\\command",
-                  QSettings::NativeFormat)
-            .value("Default")
-            .toString();
+    // get default browser start command, by protocol if possible, falling back to extension if not
+    QString command =
+        getAssociatedCommand(AssociationQueryType::Protocol, L"http");
+
+    if (command.isNull())
+    {
+        // failed to fetch default browser by protocol, try by file extension instead
+        command =
+            getAssociatedCommand(AssociationQueryType::FileExtension, L".html");
+    }
+
+    if (command.isNull())
+    {
+        // also try the equivalent .htm extension
+        command =
+            getAssociatedCommand(AssociationQueryType::FileExtension, L".htm");
+    }
+
     if (command.isNull())
     {
+        // failed to find browser command
         return QString();
     }
 
@@ -84,7 +90,7 @@ namespace chatterino {
 
 bool supportsIncognitoLinks()
 {
-#ifdef Q_OS_WIN
+#ifdef USEWINSDK
     return !getCommand().isNull();
 #else
     return false;
@@ -93,7 +99,7 @@ bool supportsIncognitoLinks()
 
 bool openLinkIncognito(const QString &link)
 {
-#ifdef Q_OS_WIN
+#ifdef USEWINSDK
     auto command = getCommand();
 
     // TODO: split command into program path and incognito argument

src/util/WindowsHelper.cpp

@@ -6,6 +6,9 @@
 
 #ifdef USEWINSDK
 
+#    include <Shlwapi.h>
+#    include <VersionHelpers.h>
+
 namespace chatterino {
 
 typedef enum MONITOR_DPI_TYPE {
@@ -17,6 +20,8 @@ typedef enum MONITOR_DPI_TYPE {
 
 typedef HRESULT(CALLBACK *GetDpiForMonitor_)(HMONITOR, MONITOR_DPI_TYPE, UINT *,
                                              UINT *);
+typedef HRESULT(CALLBACK *AssocQueryString_)(ASSOCF, ASSOCSTR, LPCWSTR, LPCWSTR,
+                                             LPWSTR, DWORD *);
 
 boost::optional<UINT> getWindowDpi(HWND hwnd)
 {
@@ -83,6 +88,55 @@ void setRegisteredForStartup(bool isRegistered)
     }
 }
 
+QString getAssociatedCommand(AssociationQueryType queryType, LPCWSTR query)
+{
+    static HINSTANCE shlwapi = LoadLibrary(L"shlwapi");
+    static auto assocQueryString = AssocQueryString_(
+        (shlwapi == NULL) ? NULL
+                          : GetProcAddress(shlwapi, "AssocQueryStringW"));
+
+    if (assocQueryString == NULL)
+    {
+        return QString();
+    }
+
+    // always error out instead of returning a truncated string when the
+    // buffer is too small - avoids race condition when the user changes their
+    // default browser between calls to AssocQueryString
+    ASSOCF flags = ASSOCF_NOTRUNCATE;
+
+    if (queryType == AssociationQueryType::Protocol)
+    {
+        // ASSOCF_IS_PROTOCOL was introduced in Windows 8
+        if (IsWindows8OrGreater())
+        {
+            flags |= ASSOCF_IS_PROTOCOL;
+        }
+        else
+        {
+            return QString();
+        }
+    }
+
+    DWORD resultSize = 0;
+    if (!SUCCEEDED(assocQueryString(flags, ASSOCSTR_COMMAND, query, NULL, NULL,
+                                    &resultSize)) ||
+        resultSize == 0)
+    {
+        return QString();
+    }
+
+    QString result;
+    auto buf = new wchar_t[resultSize];
+    if (SUCCEEDED(assocQueryString(flags, ASSOCSTR_COMMAND, query, NULL, buf,
+                                   &resultSize)))
+    {
+        result = QString::fromWCharArray(buf, resultSize);
+    }
+    delete[] buf;
+    return result;
+}
+
 }  // namespace chatterino
 
 #endif

src/util/WindowsHelper.hpp

@@ -7,12 +7,16 @@
 
 namespace chatterino {
 
+enum class AssociationQueryType { Protocol, FileExtension };
+
 boost::optional<UINT> getWindowDpi(HWND hwnd);
 void flushClipboard();
 
 bool isRegisteredForStartup();
 void setRegisteredForStartup(bool isRegistered);
 
+QString getAssociatedCommand(AssociationQueryType queryType, LPCWSTR query);
+
 }  // namespace chatterino
 
 #endif