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>

7 files changed, 192 insertions, 2 deletions

diff --git a/src/gui/CMakeLists.txt b/src/gui/CMakeLists.txt
index 802c0a2ecd..30e28cfd0e 100644
--- a/src/gui/CMakeLists.txt
+++ b/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
diff --git a/src/gui/text/qtextdocument.cpp b/src/gui/text/qtextdocument.cpp
index 0fae775bae..2e9293eb99 100644
--- a/src/gui/text/qtextdocument.cpp
+++ b/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;
 }
@@ -2119,6 +2128,30 @@ void QTextDocument::addResource(int type, const QUrl &name, const QVariant &reso
 }
 
 /*!
+    \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.
 
diff --git a/src/gui/text/qtextdocument.h b/src/gui/text/qtextdocument.h
index 23fffc4771..ea57b697a8 100644
--- a/src/gui/text/qtextdocument.h
+++ b/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);
diff --git a/src/gui/text/qtextdocument_p.cpp b/src/gui/text/qtextdocument_p.cpp
index d6da0f38d2..1f2e8d2da2 100644
--- a/src/gui/text/qtextdocument_p.cpp
+++ b/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;
diff --git a/src/gui/text/qtextdocument_p.h b/src/gui/text/qtextdocument_p.h
index b4e0f526d0..d04113b320 100644
--- a/src/gui/text/qtextdocument_p.h
+++ b/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;
diff --git a/src/gui/text/qurlresourceprovider.cpp b/src/gui/text/qurlresourceprovider.cpp
new file mode 100644
index 0000000000..6a50504471
--- /dev/null
+++ b/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
diff --git a/src/gui/text/qurlresourceprovider.h b/src/gui/text/qurlresourceprovider.h
new file mode 100644
index 0000000000..587a371a83
--- /dev/null
+++ b/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