Fix retrieving the selection/dnd data

Installing a roudtrip on the custom event queue in the wl_data_offer.offer
handler is broken because that triggers a wl_data_device.selection event,
which emits the QClipboard changed signal, so code listening to it may end
up trying to retrieve the clipboard data before the roundtrip ends.
Additionally, we're calling wl_data_offer.receive for each mime type, even
if then we never read from the fd, making the source client do work for no
reason. Instead, call wl_data_offer.receive retrieveData_sys, that is when
actually retreiving the data.

We don't need to install a roundtrip after that, just flushing out the
requests is enough, because we wait up to one second for the source client
to write into the fd.

Change-Id: I180779e375ebd5a22af7084458505a41107fab19
Reviewed-by: Robin Burchell <robin.burchell@viroteck.net>

src/plugins/platforms/wayland/qwaylanddataoffer.cpp

@@ -94,30 +94,18 @@ QWaylandMimeData::~QWaylandMimeData()
 
 void QWaylandMimeData::appendFormat(const QString &mimeType)
 {
-    if (m_types.contains(mimeType))
+    m_types << mimeType;
-        close(m_types.take(mimeType)); // Unconsumed data
     m_data.remove(mimeType); // Clear previous contents
-
-    int pipefd[2];
-    if (::pipe2(pipefd, O_CLOEXEC|O_NONBLOCK) == -1) {
-        qWarning("QWaylandMimeData: pipe2() failed");
-        return;
-    }
-
-    m_dataOffer->receive(mimeType, pipefd[1]);
-    m_display->forceRoundTrip();
-    close(pipefd[1]);
-    m_types.insert(mimeType, pipefd[0]);
 }
 
 bool QWaylandMimeData::hasFormat_sys(const QString &mimeType) const
 {
-    return m_types.contains(mimeType) || m_data.contains(mimeType);
+    return m_types.contains(mimeType);
 }
 
 QStringList QWaylandMimeData::formats_sys() const
 {
-    return m_types.keys() << m_data.keys();
+    return m_types;
 }
 
 QVariant QWaylandMimeData::retrieveData_sys(const QString &mimeType, QVariant::Type type) const
@@ -130,14 +118,24 @@ QVariant QWaylandMimeData::retrieveData_sys(const QString &mimeType, QVariant::T
     if (!m_types.contains(mimeType))
         return QVariant();
 
+    int pipefd[2];
+    if (::pipe2(pipefd, O_CLOEXEC|O_NONBLOCK) == -1) {
+        qWarning("QWaylandMimeData: pipe2() failed");
+        return QVariant();
+    }
+
+    m_dataOffer->receive(mimeType, pipefd[1]);
+    m_display->flushRequests();
+
+    close(pipefd[1]);
+
     QByteArray content;
-    int fd = m_types.take(mimeType);
+    if (readData(pipefd[0], content) != 0) {
-    if (readData(fd, content) != 0) {
         qWarning("QWaylandDataOffer: error reading data for mimeType %s", qPrintable(mimeType));
         content = QByteArray();
     }
 
-    close(fd);
+    close(pipefd[0]);
     m_data.insert(mimeType, content);
     return content;
 }

src/plugins/platforms/wayland/qwaylanddataoffer_p.h

@@ -87,7 +87,7 @@ private:
 
     mutable QWaylandDataOffer *m_dataOffer;
     QWaylandDisplay *m_display;
-    mutable QHash<QString, int> m_types;
+    mutable QStringList m_types;
     mutable QHash<QString, QByteArray> m_data;
 };