From bc3beb5461f6a5f8f6a80daf2daf7065183ee0f5 Mon Sep 17 00:00:00 2001
From: alkl58 <alkl58@protonmail.com>
Date: Thu, 9 Mar 2023 13:05:19 +0100
Subject: [PATCH] Check path validity on Windows will validate NTFS permissions
 for network drives. Signed-off-by: Alkl58 <alkl58@protonmail.com>

---
 src/common/utility.h       |  2 ++
 src/common/utility_win.cpp | 13 +++++++++++++
 src/gui/folderman.cpp      | 15 ++++++++++++++-
 3 files changed, 29 insertions(+), 1 deletion(-)

diff --git a/src/common/utility.h b/src/common/utility.h
index e19f0da6ae1ee..300d1294d0515 100644
--- a/src/common/utility.h
+++ b/src/common/utility.h
@@ -275,6 +275,8 @@ namespace Utility {
 
     OCSYNC_EXPORT QString formatWinError(long error);
 
+    OCSYNC_EXPORT bool canCreateFile(const QString &filePath);
+
     class OCSYNC_EXPORT NtfsPermissionLookupRAII
     {
     public:
diff --git a/src/common/utility_win.cpp b/src/common/utility_win.cpp
index 37b348660c0de..5279c61375c70 100644
--- a/src/common/utility_win.cpp
+++ b/src/common/utility_win.cpp
@@ -430,6 +430,19 @@ void Utility::UnixTimeToLargeIntegerFiletime(time_t t, LARGE_INTEGER *hundredNSe
     hundredNSecs->HighPart = ll >>32;
 }
 
+bool Utility::canCreateFile(const QString &filePath)
+{
+    Q_ASSERT(!filePath.isEmpty());
+    QFile testFile(filePath);
+    if (!testFile.open(QIODevice::WriteOnly)) {
+        return false;
+    }
+    testFile.close();
+    if (!testFile.remove()) {
+        return false;
+    }
+    return true;
+}
 
 QString Utility::formatWinError(long errorCode)
 {
diff --git a/src/gui/folderman.cpp b/src/gui/folderman.cpp
index 1dfc685038835..3fe657e809e55 100644
--- a/src/gui/folderman.cpp
+++ b/src/gui/folderman.cpp
@@ -1701,10 +1701,23 @@ static QString checkPathValidityRecursive(const QString &path)
         return FolderMan::tr("The selected path is not a folder!");
     }
 
+    #ifdef Q_OS_WIN
+    if (!selFile.isWritable()) {
+        // isWritable() doesn't cover all NTFS permissions
+        // try creating and removing a test file, and make sure it is excluded from sync
+        const QString pathWithSlash = !path.endsWith(QLatin1Char('/')) ? path + QLatin1Char('/') : path;
+        const QString testFileName = pathWithSlash + QStringLiteral("~$%1-write-test-file-%2").arg(OCC::Theme::instance()->appNameGUI())
+            .arg(QDateTime::currentDateTime().toMSecsSinceEpoch());
+        if (!Utility::canCreateFile(testFileName)) {
+            return FolderMan::tr("You have no permission to write to the selected folder!");
+        }
+    }
+    #else
     if (!selFile.isWritable()) {
         return FolderMan::tr("You have no permission to write to the selected folder!");
     }
-    return QString();
+    #endif
+    return {};
 }
 
 // QFileInfo::canonicalPath returns an empty string if the file does not exist.