xcb: Add support for reading the clipboard

Change-Id: I50a2c4b8f804b5a2281cbf91d30865b8c6d7c737
Reviewed-on: https://codereview.kdab.com/c/kdab/kdutils/+/133272
Reviewed-by: Miłosz Kosobucki <milosz.kosobucki@kdab.com>
Tested-by: Continuous Integration <build@kdab.com>

src/KDGui/CMakeLists.txt

@@ -26,6 +26,7 @@ if(CMAKE_SYSTEM_NAME STREQUAL "Linux")
     list(
         APPEND
         SOURCES
+        platform/linux/xcb/linux_xcb_clipboard.cpp
         platform/linux/xcb/linux_xcb_platform_event_loop.cpp
         platform/linux/xcb/linux_xcb_platform_integration.cpp
         platform/linux/xcb/linux_xcb_platform_window.cpp
@@ -36,6 +37,7 @@ if(CMAKE_SYSTEM_NAME STREQUAL "Linux")
     list(
         APPEND
         HEADERS
+        platform/linux/xcb/linux_xcb_clipboard.h
         platform/linux/xcb/linux_xcb_platform_event_loop.h
         platform/linux/xcb/linux_xcb_platform_integration.h
         platform/linux/xcb/linux_xcb_platform_window.h

src/KDGui/platform/linux/xcb/linux_xcb_clipboard.cpp

@@ -0,0 +1,105 @@
+/*
+    This file is part of KDUtils.
+
+    SPDX-FileCopyrightText: 2018-2023 Klarälvdalens Datakonsult AB, a KDAB Group company <info@kdab.com>
+    Author: Joshua Goins <joshua.goins@kdab.com>
+
+    SPDX-License-Identifier: MIT
+
+    Contact KDAB at <info@kdab.com> for commercial licensing options.
+*/
+
+#include "linux_xcb_clipboard.h"
+
+#include "linux_xcb_platform_integration.h"
+
+KDGui::LinuxXcbClipboard::LinuxXcbClipboard(KDGui::LinuxXcbPlatformIntegration *integration)
+    : m_integration{ integration }
+{
+    auto connection = m_integration->connection();
+
+    // Create a dummy window that will be dedicated to clipboard I/O
+    m_window = xcb_generate_id(connection);
+
+    xcb_create_window(
+            connection,
+            XCB_COPY_FROM_PARENT,
+            m_window,
+            m_integration->screen()->root,
+            0, 0,
+            1,
+            1,
+            10,
+            XCB_WINDOW_CLASS_INPUT_OUTPUT,
+            m_integration->screen()->root_visual,
+            0,
+            nullptr);
+
+    // Get the CLIPBOARD atom, which holds the clipboard data
+    const xcb_intern_atom_cookie_t selCookie = xcb_intern_atom(connection, false, 9, "CLIPBOARD");
+    xcb_intern_atom_reply_t *reply = xcb_intern_atom_reply(connection, selCookie, nullptr);
+    m_clipboard = reply->atom;
+
+    // Get the UTF8_STRING atom, which is used to exchange UTF8 data between clients
+    const xcb_intern_atom_cookie_t utf8Cookie = xcb_intern_atom(connection, false, 11, "UTF8_STRING");
+    reply = xcb_intern_atom_reply(connection, utf8Cookie, nullptr);
+    m_utf8 = reply->atom;
+}
+
+KDGui::LinuxXcbClipboard::~LinuxXcbClipboard()
+{
+    xcb_destroy_window(m_integration->connection(), m_window);
+}
+
+std::string KDGui::LinuxXcbClipboard::text()
+{
+    auto connection = m_integration->connection();
+
+    const xcb_get_selection_owner_cookie_t ownerCookie = xcb_get_selection_owner(m_integration->connection(), m_clipboard);
+    auto ownerReply = xcb_get_selection_owner_reply(connection, ownerCookie, nullptr);
+
+    // No one has any clipboard data
+    if (ownerReply == nullptr || ownerReply->owner == 0) {
+        return "";
+    }
+
+    xcb_convert_selection(connection, m_window, m_clipboard, m_utf8, m_clipboard, XCB_TIME_CURRENT_TIME);
+    xcb_flush(connection);
+
+    // Await the selection reply from the other client
+    for (;;) {
+        if (auto xcbEvent = xcb_poll_for_event(connection)) {
+            const auto eventType = xcbEvent->response_type & 0x7f;
+
+            if (eventType == XCB_SELECTION_NOTIFY) {
+                break;
+            }
+        }
+    }
+
+    auto propertyCookie = xcb_get_property(connection, 1, m_window, m_clipboard, m_utf8, 0, 0);
+    auto propertyReply = xcb_get_property_reply(connection, propertyCookie, nullptr);
+
+    const uint32_t ret = propertyReply->bytes_after;
+    if (ret == 0) {
+        return "";
+    }
+
+    propertyCookie = xcb_get_property(connection, 1, m_window, m_clipboard, m_utf8, 0, (ret + 4) >> 2);
+    propertyReply = xcb_get_property_reply(connection, propertyCookie, nullptr);
+
+    const int clipboardLength = xcb_get_property_value_length(propertyReply);
+    if (clipboardLength == 0) {
+        return "";
+    }
+
+    std::vector<char> buffer(clipboardLength);
+    std::copy_n(reinterpret_cast<char *>(xcb_get_property_value(propertyReply)), clipboardLength, buffer.data());
+
+    return buffer.data();
+}
+
+void KDGui::LinuxXcbClipboard::setText(std::string_view text)
+{
+    // TODO: xcb stub
+}

src/KDGui/platform/linux/xcb/linux_xcb_clipboard.h

@@ -0,0 +1,40 @@
+/*
+    This file is part of KDUtils.
+
+    SPDX-FileCopyrightText: 2018-2023 Klarälvdalens Datakonsult AB, a KDAB Group company <info@kdab.com>
+    Author: Joshua Goins <joshua.goins@kdab.com>
+
+    SPDX-License-Identifier: MIT
+
+    Contact KDAB at <info@kdab.com> for commercial licensing options.
+*/
+
+#pragma once
+
+#include <cstdint>
+#include <string>
+
+#include <KDGui/abstract_clipboard.h>
+
+#include <xcb/xcb.h>
+
+namespace KDGui {
+
+class LinuxXcbPlatformIntegration;
+
+class LinuxXcbClipboard : public AbstractClipboard
+{
+public:
+    LinuxXcbClipboard(KDGui::LinuxXcbPlatformIntegration *integration);
+    ~LinuxXcbClipboard();
+
+    std::string text() override;
+    void setText(std::string_view text) override;
+
+private:
+    KDGui::LinuxXcbPlatformIntegration *m_integration{ nullptr };
+    xcb_atom_t m_clipboard, m_utf8;
+    uint32_t m_window;
+};
+
+} // namespace KDGui

src/KDGui/platform/linux/xcb/linux_xcb_platform_integration.cpp

@@ -38,6 +38,8 @@ LinuxXcbPlatformIntegration::LinuxXcbPlatformIntegration()
     m_screen = iter.data;
 
     dumpScreenInfo(m_screen);
+
+    m_clipboard = std::make_unique<LinuxXcbClipboard>(this);
 }
 
 LinuxXcbPlatformIntegration::~LinuxXcbPlatformIntegration()
@@ -49,6 +51,11 @@ LinuxXcbPlatformIntegration::~LinuxXcbPlatformIntegration()
         SPDLOG_DEBUG("Destroyed xcb_connection");
 }
 
+AbstractClipboard *LinuxXcbPlatformIntegration::clipboard()
+{
+    return m_clipboard.get();
+}
+
 LinuxXkbKeyboard *LinuxXcbPlatformIntegration::keyboard()
 {
     if (!m_keyboard)

src/KDGui/platform/linux/xcb/linux_xcb_platform_integration.h

@@ -14,6 +14,7 @@
 #include <KDGui/abstract_gui_platform_integration.h>
 #include <KDGui/platform/linux/xcb/linux_xcb_platform_event_loop.h>
 #include <KDGui/platform/linux/xcb/linux_xcb_platform_window.h>
+#include <KDGui/platform/linux/xcb/linux_xcb_clipboard.h>
 #include <KDFoundation/logging.h>
 
 #include <xcb/xcb.h>
@@ -30,6 +31,8 @@ class KDGUI_API LinuxXcbPlatformIntegration : public AbstractGuiPlatformIntegrat
     LinuxXcbPlatformIntegration();
     ~LinuxXcbPlatformIntegration() override;
 
+    AbstractClipboard *clipboard() override;
+
     std::shared_ptr<spdlog::logger> logger() { return m_logger; }
 
     LinuxXkbKeyboard *keyboard();
@@ -44,12 +47,6 @@ class KDGUI_API LinuxXcbPlatformIntegration : public AbstractGuiPlatformIntegrat
     void unregisterWindowForEvents(xcb_window_t xcbWindow) { m_windows.erase(xcbWindow); }
     LinuxXcbPlatformWindow *window(xcb_window_t xcbWindow) { return m_windows.at(xcbWindow); }
 
-    AbstractClipboard *clipboard() override
-    {
-        // TODO(xcb): Implement clipboard
-        return nullptr;
-    }
-
 private:
     LinuxXcbPlatformEventLoop *createPlatformEventLoopImpl() override;
     LinuxXcbPlatformWindow *createPlatformWindowImpl(Window *window) override;
@@ -62,6 +59,7 @@ class KDGUI_API LinuxXcbPlatformIntegration : public AbstractGuiPlatformIntegrat
     xcb_screen_t *m_screen{ nullptr };
     std::unique_ptr<LinuxXkbKeyboard> m_keyboard;
     std::map<xcb_window_t, LinuxXcbPlatformWindow *> m_windows;
+    std::unique_ptr<LinuxXcbClipboard> m_clipboard;
 };
 
 } // namespace KDGui