Introduce QUrlResourceProvider to load resources for HTML

QTextDocument and the text editor classes suggest to override
their loadResource() methods to provide data associated with
a text document. This approach has the following drawbacks:
- it requires subclassing
- there is no way to set a global resource provider
- QLabel is missing virtual loadResource() method and
  it can't be added without breaking ABI

QUrlResourceProvider is designed to solve these issues.
One should create a derived class that implements
QUrlResourceProvider::resource(). The objects of the derived
class then can be set for any text document.
The default resource provider can be set with
QUrlResourceProvider::setDefaultProvider().
This change also adds QLabel::setResourceProvider(),
which doesn't break ABI.

[ChangeLog][QtGui][Text] Introduced QUrlResourceProvider that allows to
load resources for HTML. It is intended to replace the use of
QTextDocument::loadResource().

Change-Id: Iaf19b229f522a73508f20715257450fe58f68daf
Reviewed-by: Konstantin Ritt <ritt.ks@gmail.com>
Reviewed-by: Lars Knoll <lars.knoll@qt.io>

src/gui/CMakeLists.txt

@@ -242,6 +242,7 @@ qt_internal_add_module(Gui
         text/qtextobject.cpp text/qtextobject.h text/qtextobject_p.h
         text/qtextoption.cpp text/qtextoption.h
         text/qtexttable.cpp text/qtexttable.h text/qtexttable_p.h
+        text/qurlresourceprovider.cpp text/qurlresourceprovider.h
         util/qabstractlayoutstyleinfo.cpp util/qabstractlayoutstyleinfo_p.h
         util/qastchandler.cpp util/qastchandler_p.h
         util/qdesktopservices.cpp util/qdesktopservices.h

src/gui/text/qtextdocument.cpp

@@ -46,6 +46,7 @@
 #include "qtextdocumentfragment_p.h"
 #include "qtexttable.h"
 #include "qtextlist.h"
+#include "qurlresourceprovider.h"
 #include <qdebug.h>
 #if QT_CONFIG(regularexpression)
 #include <qregularexpression.h>
@@ -354,6 +355,7 @@ QTextDocument *QTextDocument::clone(QObject *parent) const
     priv->setDefaultFont(d->defaultFont());
     priv->resources = d->resources;
     priv->cachedResources.clear();
+    priv->resourceProvider = d->resourceProvider;
 #ifndef QT_NO_CSSPARSER
     priv->defaultStyleSheet = d->defaultStyleSheet;
     priv->parsedDefaultStyleSheet = d->parsedDefaultStyleSheet;
@@ -2087,8 +2089,15 @@ QVariant QTextDocument::resource(int type, const QUrl &name) const
     QVariant r = d->resources.value(url);
     if (!r.isValid()) {
         r = d->cachedResources.value(url);
-        if (!r.isValid())
+        if (!r.isValid()) {
             r = const_cast<QTextDocument *>(this)->loadResource(type, url);
+            if (!r.isValid()) {
+                if (d->resourceProvider)
+                    r = d->resourceProvider->resource(url);
+                else if (auto defaultProvider = QUrlResourceProvider::defaultProvider())
+                    r = defaultProvider->resource(url);
+            }
+        }
     }
     return r;
 }
@@ -2118,6 +2127,30 @@ void QTextDocument::addResource(int type, const QUrl &name, const QVariant &reso
     d->resources.insert(name, resource);
 }
 
+/*!
+    \since 6.1
+
+    Returns the resource provider for this text document.
+*/
+QUrlResourceProvider *QTextDocument::resourceProvider() const
+{
+    Q_D(const QTextDocument);
+    return d->resourceProvider;
+}
+
+/*!
+    \since 6.1
+
+    Sets the \a provider of resources for the text document.
+
+    \note The text document \e{does not} take ownership of the \a provider.
+*/
+void QTextDocument::setResourceProvider(QUrlResourceProvider *provider)
+{
+    Q_D(QTextDocument);
+    d->resourceProvider = provider;
+}
+
 /*!
     Loads data of the specified \a type from the resource with the
     given \a name.

src/gui/text/qtextdocument.h

@@ -68,6 +68,7 @@ class QVariant;
 class QRectF;
 class QTextOption;
 class QTextCursor;
+class QUrlResourceProvider;
 
 
 namespace Qt
@@ -239,6 +240,9 @@ public:
     QVariant resource(int type, const QUrl &name) const;
     void addResource(int type, const QUrl &name, const QVariant &resource);
 
+    QUrlResourceProvider *resourceProvider() const;
+    void setResourceProvider(QUrlResourceProvider *provider);
+
     QList<QTextFormat> allFormats() const;
 
     void markContentsDirty(int from, int length);

src/gui/text/qtextdocument_p.cpp

@@ -52,6 +52,7 @@
 #include "qtextdocumentlayout_p.h"
 #include "qtexttable.h"
 #include "qtextengine_p.h"
+#include "qurlresourceprovider.h"
 
 #include <stdlib.h>
 
@@ -186,7 +187,8 @@ QTextDocumentPrivate::QTextDocumentPrivate()
     docChangeLength(0),
     framesDirty(true),
     rtFrame(nullptr),
-    initialBlockCharFormatIndex(-1) // set correctly later in init()
+    initialBlockCharFormatIndex(-1), // set correctly later in init()
+    resourceProvider(nullptr)
 {
     editBlock = 0;
     editBlockCursorPosition = -1;

src/gui/text/qtextdocument_p.h

@@ -366,6 +366,7 @@ private:
     QMap<int, QTextObject *> objects;
     QMap<QUrl, QVariant> resources;
     QMap<QUrl, QVariant> cachedResources;
+    QUrlResourceProvider *resourceProvider;
     QString defaultStyleSheet;
 
     int lastBlockCount;

src/gui/text/qurlresourceprovider.cpp

@@ -0,0 +1,88 @@
+/****************************************************************************
+**
+** Copyright (C) 2020 Alexander Volkov <avolkov@astralinux.ru>
+** Contact: https://www.qt.io/licensing/
+**
+** This file is part of the QtGui module of the Qt Toolkit.
+**
+** $QT_BEGIN_LICENSE:LGPL$
+** Commercial License Usage
+** Licensees holding valid commercial Qt licenses may use this file in
+** accordance with the commercial license agreement provided with the
+** Software or, alternatively, in accordance with the terms contained in
+** a written agreement between you and The Qt Company. For licensing terms
+** and conditions see https://www.qt.io/terms-conditions. For further
+** information use the contact form at https://www.qt.io/contact-us.
+**
+** GNU Lesser General Public License Usage
+** Alternatively, this file may be used under the terms of the GNU Lesser
+** General Public License version 3 as published by the Free Software
+** Foundation and appearing in the file LICENSE.LGPL3 included in the
+** packaging of this file. Please review the following information to
+** ensure the GNU Lesser General Public License version 3 requirements
+** will be met: https://www.gnu.org/licenses/lgpl-3.0.html.
+**
+** GNU General Public License Usage
+** Alternatively, this file may be used under the terms of the GNU
+** General Public License version 2.0 or (at your option) the GNU General
+** Public license version 3 or any later version approved by the KDE Free
+** Qt Foundation. The licenses are as published by the Free Software
+** Foundation and appearing in the file LICENSE.GPL2 and LICENSE.GPL3
+** included in the packaging of this file. Please review the following
+** information to ensure the GNU General Public License requirements will
+** be met: https://www.gnu.org/licenses/gpl-2.0.html and
+** https://www.gnu.org/licenses/gpl-3.0.html.
+**
+** $QT_END_LICENSE$
+**
+****************************************************************************/
+
+#include "qurlresourceprovider.h"
+
+#include <QtCore/qatomic.h>
+
+QT_BEGIN_NAMESPACE
+
+/*!
+    \class QUrlResourceProvider
+    \inmodule QtGui
+    \since 6.1
+    \brief The QUrlResourceProvider is the base class of resource providers for QTextDocument.
+    \note An implementation should be thread-safe if it can be accessed from different threads,
+    e.g. when the default resource provider lives in the main thread and a QTexDocument lives
+    outside the main thread.
+*/
+
+static QAtomicPointer<QUrlResourceProvider> qt_provider;
+
+/*!
+    Destroys the resource provider.
+*/
+QUrlResourceProvider::~QUrlResourceProvider()
+{
+    qt_provider.testAndSetRelease(this, nullptr);
+}
+
+/*!
+    \fn virtual QVariant QUrlResourceProvider::resource(const QUrl &url) = 0;
+
+    Returns data specified by the \a url.
+*/
+
+/*!
+    Returns the default resource provider.
+*/
+QUrlResourceProvider *QUrlResourceProvider::defaultProvider()
+{
+    return qt_provider.loadAcquire();
+}
+
+/*!
+    Set the default resource provider to \a provider.
+*/
+void QUrlResourceProvider::setDefaultProvider(QUrlResourceProvider *provider)
+{
+    qt_provider.storeRelease(provider);
+}
+
+QT_END_NAMESPACE

src/gui/text/qurlresourceprovider.h

@@ -0,0 +1,61 @@
+/****************************************************************************
+**
+** Copyright (C) 2020 Alexander Volkov <avolkov@astralinux.ru>
+** Contact: https://www.qt.io/licensing/
+**
+** This file is part of the QtGui module of the Qt Toolkit.
+**
+** $QT_BEGIN_LICENSE:LGPL$
+** Commercial License Usage
+** Licensees holding valid commercial Qt licenses may use this file in
+** accordance with the commercial license agreement provided with the
+** Software or, alternatively, in accordance with the terms contained in
+** a written agreement between you and The Qt Company. For licensing terms
+** and conditions see https://www.qt.io/terms-conditions. For further
+** information use the contact form at https://www.qt.io/contact-us.
+**
+** GNU Lesser General Public License Usage
+** Alternatively, this file may be used under the terms of the GNU Lesser
+** General Public License version 3 as published by the Free Software
+** Foundation and appearing in the file LICENSE.LGPL3 included in the
+** packaging of this file. Please review the following information to
+** ensure the GNU Lesser General Public License version 3 requirements
+** will be met: https://www.gnu.org/licenses/lgpl-3.0.html.
+**
+** GNU General Public License Usage
+** Alternatively, this file may be used under the terms of the GNU
+** General Public License version 2.0 or (at your option) the GNU General
+** Public license version 3 or any later version approved by the KDE Free
+** Qt Foundation. The licenses are as published by the Free Software
+** Foundation and appearing in the file LICENSE.GPL2 and LICENSE.GPL3
+** included in the packaging of this file. Please review the following
+** information to ensure the GNU General Public License requirements will
+** be met: https://www.gnu.org/licenses/gpl-2.0.html and
+** https://www.gnu.org/licenses/gpl-3.0.html.
+**
+** $QT_END_LICENSE$
+**
+****************************************************************************/
+
+#ifndef QURLRESOURCEPROVIDER_H
+#define QURLRESOURCEPROVIDER_H
+
+#include <QtGui/qtguiglobal.h>
+#include <QtCore/qvariant.h>
+
+QT_BEGIN_NAMESPACE
+
+
+class Q_GUI_EXPORT QUrlResourceProvider
+{
+public:
+    virtual ~QUrlResourceProvider();
+    virtual QVariant resource(const QUrl &url) = 0;
+
+    static QUrlResourceProvider *defaultProvider();
+    static void setDefaultProvider(QUrlResourceProvider *provider);
+};
+
+QT_END_NAMESPACE
+
+#endif // QURLRESOURCEPROVIDER_H

src/widgets/widgets/qlabel.cpp

@@ -100,7 +100,8 @@ QLabelPrivate::QLabelPrivate()
       validCursor(false),
       onAnchor(false),
 #endif
-      openExternalLinks(false)
+      openExternalLinks(false),
+      resourceProvider(nullptr)
 {
 }
 
@@ -1423,6 +1424,32 @@ void QLabel::setTextFormat(Qt::TextFormat format)
     }
 }
 
+/*!
+    \since 6.1
+
+    Returns the resource provider for rich text of this label.
+*/
+QUrlResourceProvider *QLabel::resourceProvider() const
+{
+    Q_D(const QLabel);
+    return d->control ? d->control->document()->resourceProvider() : d->resourceProvider;
+}
+
+/*!
+    \since 6.1
+
+    Sets the \a provider of resources for rich text of this label.
+
+    \note The label \e{does not} take ownership of the \a provider.
+*/
+void QLabel::setResourceProvider(QUrlResourceProvider *provider)
+{
+    Q_D(QLabel);
+    d->resourceProvider = provider;
+    if (d->control != nullptr)
+        d->control->document()->setResourceProvider(provider);
+}
+
 /*!
   \reimp
 */
@@ -1589,6 +1616,8 @@ void QLabelPrivate::ensureTextControl() const
         control = new QWidgetTextControl(const_cast<QLabel *>(q));
         control->document()->setUndoRedoEnabled(false);
         control->document()->setDefaultFont(q->font());
+        if (resourceProvider != nullptr)
+            control->document()->setResourceProvider(resourceProvider);
         control->setTextInteractionFlags(textInteractionFlags);
         control->setOpenExternalLinks(openExternalLinks);
         control->setPalette(q->palette());

src/widgets/widgets/qlabel.h

@@ -49,6 +49,7 @@ QT_REQUIRE_CONFIG(label);
 QT_BEGIN_NAMESPACE
 
 
+class QUrlResourceProvider;
 class QLabelPrivate;
 
 class Q_WIDGETS_EXPORT QLabel : public QFrame
@@ -92,6 +93,9 @@ public:
     Qt::TextFormat textFormat() const;
     void setTextFormat(Qt::TextFormat);
 
+    QUrlResourceProvider *resourceProvider() const;
+    void setResourceProvider(QUrlResourceProvider *provider);
+
     Qt::Alignment alignment() const;
     void setAlignment(Qt::Alignment);
 

src/widgets/widgets/qlabel_p.h

@@ -154,6 +154,7 @@ public:
 #endif
     uint openExternalLinks : 1;
     // <-- space for more bit field values here
+    QUrlResourceProvider *resourceProvider;
 
     friend class QMessageBoxPrivate;
 };

src/widgets/widgets/qwidgettextcontrol.cpp

@@ -2677,6 +2677,7 @@ void QWidgetTextControl::print(QPagedPaintDevice *printer) const
         if (!d->cursor.hasSelection())
             return;
         tempDoc = new QTextDocument(const_cast<QTextDocument *>(doc));
+        tempDoc->setResourceProvider(doc->resourceProvider());
         tempDoc->setMetaInformation(QTextDocument::DocumentTitle, doc->metaInformation(QTextDocument::DocumentTitle));
         tempDoc->setPageSize(doc->pageSize());
         tempDoc->setDefaultFont(doc->defaultFont());

tests/auto/gui/text/qtextdocument/tst_qtextdocument.cpp

@@ -47,6 +47,7 @@
 #include <qimage.h>
 #include <qtextlayout.h>
 #include <QDomDocument>
+#include <qurlresourceprovider.h>
 #include "common.h"
 
 // #define DEBUG_WRITE_OUTPUT
@@ -192,6 +193,8 @@ private slots:
     void clearUndoRedoStacks();
     void mergeFontFamilies();
 
+    void resourceProvider();
+
 private:
     void backgroundImage_checkExpectedHtml(const QTextDocument &doc);
     void buildRegExpData();
@@ -3593,6 +3596,28 @@ void tst_QTextDocument::clearUndoRedoStacks()
     QVERIFY(!doc.isUndoAvailable());
 }
 
+class UrlResourceProvider : public QUrlResourceProvider
+{
+public:
+    QVariant resource(const QUrl &url) override
+    {
+        resourseUrl = url;
+        return QVariant();
+    }
+
+    QUrl resourseUrl;
+};
+
+void tst_QTextDocument::resourceProvider()
+{
+    QTextDocument doc;
+    UrlResourceProvider resourceProvider;
+    doc.setResourceProvider(&resourceProvider);
+    QUrl url("test://img");
+    doc.setHtml(QStringLiteral("<img src='%1'/>").arg(url.toString()));
+    doc.resource(QTextDocument::UserResource, url);
+    QCOMPARE(url, resourceProvider.resourseUrl);
+}
 
 QTEST_MAIN(tst_QTextDocument)
 #include "tst_qtextdocument.moc"

tests/auto/widgets/widgets/qlabel/tst_qlabel.cpp

@@ -40,6 +40,7 @@
 #include <qmessagebox.h>
 #include <qfontmetrics.h>
 #include <qmath.h>
+#include <qurlresourceprovider.h>
 #include <private/qlabel_p.h>
 
 class Widget : public QWidget
@@ -103,6 +104,8 @@ private Q_SLOTS:
     void taskQTBUG_48157_dprPixmap();
     void taskQTBUG_48157_dprMovie();
 
+    void resourceProvider();
+
 private:
     QLabel *testWidget;
     QPointer<Widget> test_box;
@@ -596,5 +599,28 @@ void tst_QLabel::taskQTBUG_48157_dprMovie()
     QCOMPARE(label.sizeHint(), movie.currentPixmap().size() / movie.currentPixmap().devicePixelRatio());
 }
 
+class UrlResourceProvider : public QUrlResourceProvider
+{
+public:
+    QVariant resource(const QUrl &url) override
+    {
+        resourseUrl = url;
+        return QVariant();
+    }
+
+    QUrl resourseUrl;
+};
+
+void tst_QLabel::resourceProvider()
+{
+    QLabel label;
+    UrlResourceProvider resourceProvider;
+    label.setResourceProvider(&resourceProvider);
+    QUrl url("test://img");
+    label.setText(QStringLiteral("<img src='%1'/>").arg(url.toString()));
+    label.show();
+    QCOMPARE(url, resourceProvider.resourseUrl);
+}
+
 QTEST_MAIN(tst_QLabel)
 #include "tst_qlabel.moc"