Win: work around (estimated) 32k char limit for OutputDebugString

Reaching a certain number of characters, OutputDebugString will just eat
the string and not give any output. As there is no way of handling that
error properly we divide the string into usable chunks.

Fixes: QTBUG-80996
Change-Id: Ic7ef34c48c212cbaec3a03790d1020506b7b4319
Reviewed-by: Miguel Costa <miguel.costa@qt.io>
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@qt.io>
Reviewed-by: Mårten Nordheim <marten.nordheim@qt.io>

1 files changed, 25 insertions, 5 deletions

diff --git a/src/corelib/global/qlogging.cpp b/src/corelib/global/qlogging.cpp
index 5a7f8242de..c1dd04f03c 100644
--- a/src/corelib/global/qlogging.cpp
+++ b/src/corelib/global/qlogging.cpp
@@ -1669,14 +1669,34 @@ static bool android_default_message_handler(QtMsgType type,
 #endif //Q_OS_ANDROID
 
 #ifdef Q_OS_WIN
+static void win_outputDebugString_helper(QStringView message)
+{
+    const int maxOutputStringLength = 32766;
+    static QBasicMutex m;
+    auto locker = qt_unique_lock(m);
+    // fast path: Avoid string copies if one output is enough
+    if (message.length() <= maxOutputStringLength) {
+        OutputDebugString(reinterpret_cast<const wchar_t *>(message.utf16()));
+    } else {
+        wchar_t *messagePart = new wchar_t[maxOutputStringLength + 1];
+        for (int i = 0; i < message.length(); i += maxOutputStringLength ) {
+            const int length = std::min(message.length() - i, maxOutputStringLength );
+            const int len = message.mid(i, length).toWCharArray(messagePart);
+            Q_ASSERT(len == length);
+            messagePart[len] = 0;
+            OutputDebugString(messagePart);
+        }
+        delete[] messagePart;
+    }
+}
+
 static bool win_message_handler(QtMsgType type, const QMessageLogContext &context, const QString &message)
 {
     if (shouldLogToStderr())
         return false; // Leave logging up to stderr handler
 
-    QString formattedMessage = qFormatLogMessage(type, context, message);
-    formattedMessage.append(QLatin1Char('\n'));
-    OutputDebugString(reinterpret_cast<const wchar_t *>(formattedMessage.utf16()));
+    const QString formattedMessage = qFormatLogMessage(type, context, message).append('\n');
+    win_outputDebugString_helper(formattedMessage);
 
     return true; // Prevent further output to stderr
 }
@@ -1832,11 +1852,11 @@ static void qt_message_print(QtMsgType msgType, const QMessageLogContext &contex
 static void qt_message_print(const QString &message)
 {
 #if defined(Q_OS_WINRT)
-    OutputDebugString(reinterpret_cast<const wchar_t*>(message.utf16()));
+    win_outputDebugString_helper(message);
     return;
 #elif defined(Q_OS_WIN) && !defined(QT_BOOTSTRAPPED)
     if (!shouldLogToStderr()) {
-        OutputDebugString(reinterpret_cast<const wchar_t*>(message.utf16()));
+        win_outputDebugString_helper(message);
         return;
     }
 #endif