Add VNC clipboard sync

RFB's ServerCutText/ClientCutText messages are much simpler than RDP's
CLIPRDR channel (no format-list/format-request negotiation -- text is
just sent directly in both directions), so ServerCutText now emits
remoteClipboardTextChanged instead of being discarded, and
VncSessionBackend overrides setClipboardText to send ClientCutText
immediately. Extends session_tab.cpp's clipboard-sync gate to cover
VNC alongside RDP; the QClipboard wiring itself was already
protocol-agnostic. Latin-1 only, per RFB's wire format -- no Unicode
clipboard extension is in scope.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

src/session_tab.cpp

@@ -77,8 +77,9 @@ SessionTab::SessionTab(const Profile& profile,
       m_terminalFontPointSize(preferences.terminalFontPointSize > 0
                                   ? preferences.terminalFontPointSize
                                   : 0),
-      m_clipboardSyncSupported(profile.protocol.compare(QStringLiteral("RDP"), Qt::CaseInsensitive)
+      m_clipboardSyncSupported(
-                                == 0),
+          profile.protocol.compare(QStringLiteral("RDP"), Qt::CaseInsensitive) == 0
+          || profile.protocol.compare(QStringLiteral("VNC"), Qt::CaseInsensitive) == 0),
       m_sshTerminal(nullptr),
       m_rdpDisplay(nullptr),
       m_vncDisplay(nullptr),

src/vnc_session_backend.cpp

@@ -263,6 +263,16 @@ void VncSessionBackend::sendMouseWheelEvent(int x, int y, int deltaX, int deltaY
     }
 }
 
+void VncSessionBackend::setClipboardText(const QString& text)
+{
+    if (m_socket->state() != QAbstractSocket::ConnectedState) {
+        return;
+    }
+    // Unlike RDP's CLIPRDR (list -> server request -> response), RFB's
+    // ClientCutText has no negotiation: send it immediately.
+    sendClientCutText(text);
+}
+
 void VncSessionBackend::onSocketConnected()
 {
     emit eventLogged(QStringLiteral("TCP connection established; waiting for VNC handshake."));
@@ -465,6 +475,19 @@ void VncSessionBackend::sendWheelClick(quint8 wheelBit)
     m_socket->write(release);
 }
 
+void VncSessionBackend::sendClientCutText(const QString& text)
+{
+    // Latin-1 only, matching ServerCutText's decode above -- RFB has no
+    // Unicode clipboard extension in scope here.
+    const QByteArray latin1 = text.toLatin1();
+    QByteArray msg;
+    msg.append(kMsgClientCutText);
+    msg.append(3, char(0)); // padding
+    appendU32BE(msg, static_cast<quint32>(latin1.size()));
+    msg.append(latin1);
+    m_socket->write(msg);
+}
+
 void VncSessionBackend::finishHandshakeIntoRunningState()
 {
     emit remoteDesktopSizeChanged(m_framebuffer.width(), m_framebuffer.height());
@@ -895,10 +918,13 @@ void VncSessionBackend::processReceiveBuffer()
             if (!haveBytes(static_cast<int>(m_pendingLength))) {
                 return;
             }
-            // Clipboard sync is out of scope for this pass; consume and
+            // RFB's ServerCutText is Latin-1 only (RFC 6143 SS7.5.4) -- no
-            // discard so the byte stream stays in sync.
+            // Unicode extension is implemented, unlike RDP's CLIPRDR.
+            const QString text =
+                QString::fromLatin1(m_recvBuffer.left(static_cast<int>(m_pendingLength)));
             m_recvBuffer.remove(0, static_cast<int>(m_pendingLength));
             m_rfbState = RfbState::WaitingServerMessageType;
+            emit remoteClipboardTextChanged(text);
             break;
         }
         }

src/vnc_session_backend.h

@@ -21,7 +21,8 @@ class QTcpSocket;
 // Scope (see plan / issue #3 for the full rationale): standard VNC
 // Authentication (security type 2) and no-auth (type 1) only -- not
 // Apple's Screen Sharing scheme (type 30). Raw + CopyRect encodings only.
-// No dynamic resize, no remote cursor shape sync, no clipboard sync.
+// No dynamic resize, no remote cursor shape sync. Clipboard sync (Latin-1
+// only, per RFB's ServerCutText/ClientCutText) is supported.
 class VncSessionBackend : public SessionBackend
 {
     Q_OBJECT
@@ -52,6 +53,7 @@ public slots:
     void sendMouseMoveEvent(int x, int y) override;
     void sendMouseButtonEvent(int x, int y, int button, bool pressed) override;
     void sendMouseWheelEvent(int x, int y, int deltaX, int deltaY) override;
+    void setClipboardText(const QString& text) override;
 
 private slots:
     void onSocketConnected();
@@ -129,6 +131,7 @@ private:
     void onRectangleFinished();
     void sendPointerEvent();
     void sendWheelClick(quint8 wheelBit);
+    void sendClientCutText(const QString& text);
 };
 
 #endif

tests/test_vnc_session_backend.cpp

@@ -110,6 +110,8 @@ private slots:
     void rawFramebufferUpdateProducesExpectedPixels();
     void copyRectEncodingDoesNotFailConnection();
     void unannouncedEncodingFailsConnectionWithClearMessage();
+    void serverCutTextEmitsRemoteClipboardTextChanged();
+    void setClipboardTextSendsClientCutText();
 
 private:
     std::unique_ptr<FakeVncServer> m_server;
@@ -620,5 +622,102 @@ void TestVncSessionBackend::unannouncedEncodingFailsConnectionWithClearMessage()
     QVERIFY(m_lastErrorDisplay.contains(QStringLiteral("non-compliant")));
 }
 
+void TestVncSessionBackend::serverCutTextEmitsRemoteClipboardTextChanged()
+{
+    QString lastClipboardText;
+    connect(m_backend.get(), &SessionBackend::remoteClipboardTextChanged, this,
+            [&lastClipboardText](const QString& text) { lastClipboardText = text; });
+
+    connect(m_server.get(), &FakeVncServer::clientConnected, this, [this]() {
+        m_server->sendWhenConnected(QByteArray("RFB 003.008\n"));
+    });
+    connect(m_server.get(), &FakeVncServer::dataReceived, this, [this]() {
+        switch (m_server->nextStep()) {
+        case 0: {
+            QByteArray securityTypes;
+            securityTypes.append(char(1));
+            securityTypes.append(char(1));
+            m_server->sendWhenConnected(securityTypes);
+            break;
+        }
+        case 1:
+            m_server->sendWhenConnected(QByteArray(4, char(0))); // SecurityResult: OK
+            break;
+        case 2: { // ClientInit -- reply with ServerInit, then a ServerCutText message
+            QByteArray serverInit;
+            serverInit.append(char(0)); serverInit.append(char(1));
+            serverInit.append(char(0)); serverInit.append(char(1));
+            serverInit.append(QByteArray(16, char(0)));
+            serverInit.append(QByteArray(4, char(0)));
+
+            QByteArray cutText;
+            cutText.append(char(3)); // message-type: ServerCutText
+            cutText.append(3, char(0)); // padding
+            const QByteArray text = QByteArray("hello clipboard");
+            cutText.append(char(0)); cutText.append(char(0)); cutText.append(char(0));
+            cutText.append(static_cast<char>(text.size())); // length (BE, fits one byte here)
+
+            m_server->sendWhenConnected(serverInit + cutText + text);
+            break;
+        }
+        default:
+            break;
+        }
+    });
+
+    m_backend->connectSession(makeOptions());
+    QTRY_COMPARE(lastClipboardText, QStringLiteral("hello clipboard"));
+}
+
+void TestVncSessionBackend::setClipboardTextSendsClientCutText()
+{
+    connect(m_server.get(), &FakeVncServer::clientConnected, this, [this]() {
+        m_server->sendWhenConnected(QByteArray("RFB 003.008\n"));
+    });
+    connect(m_server.get(), &FakeVncServer::dataReceived, this, [this]() {
+        switch (m_server->nextStep()) {
+        case 0: {
+            QByteArray securityTypes;
+            securityTypes.append(char(1));
+            securityTypes.append(char(1));
+            m_server->sendWhenConnected(securityTypes);
+            break;
+        }
+        case 1:
+            m_server->sendWhenConnected(QByteArray(4, char(0))); // SecurityResult: OK
+            break;
+        case 2: { // ClientInit
+            QByteArray serverInit;
+            serverInit.append(char(0)); serverInit.append(char(1));
+            serverInit.append(char(0)); serverInit.append(char(1));
+            serverInit.append(QByteArray(16, char(0)));
+            serverInit.append(QByteArray(4, char(0)));
+            m_server->sendWhenConnected(serverInit);
+            break;
+        }
+        default:
+            break;
+        }
+    });
+
+    m_backend->connectSession(makeOptions());
+    QTRY_COMPARE(m_lastState, SessionState::Connected);
+
+    m_backend->setClipboardText(QStringLiteral("hi"));
+
+    // The exact ClientCutText bytes must eventually appear at the tail of
+    // whatever the fake server received -- checked with endsWith() rather
+    // than an exact match on the whole buffer, since exactly how the
+    // preceding handshake/SetEncodings/FramebufferUpdateRequest bytes get
+    // chunked into TCP reads isn't guaranteed and doesn't matter here.
+    QByteArray expected;
+    expected.append(char(6)); // message-type: ClientCutText
+    expected.append(3, char(0)); // padding
+    expected.append(char(0)); expected.append(char(0)); expected.append(char(0));
+    expected.append(char(2)); // length = 2
+    expected.append("hi");
+    QTRY_VERIFY(m_server->received.endsWith(expected));
+}
+
 QTEST_GUILESS_MAIN(TestVncSessionBackend)
 #include "test_vnc_session_backend.moc"