From e993df877131cfafbf1a3578dbef233a3041a82f Mon Sep 17 00:00:00 2001 From: David Faure Date: Thu, 27 Dec 2012 07:42:27 -0500 Subject: Add class QSaveFile. This QIODevice uses a temporary file for writing, so that in case of write errors, the writing operation is canceled, without losing any existing file. It also avoids having a partially-written file visible by other processes, at the final destination. Change-Id: I9482df45751cb890b1b6f1382ec2eea3eb980627 Reviewed-by: Thiago Macieira --- src/corelib/io/qsavefile.cpp | 316 +++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 316 insertions(+) create mode 100644 src/corelib/io/qsavefile.cpp (limited to 'src/corelib/io/qsavefile.cpp') diff --git a/src/corelib/io/qsavefile.cpp b/src/corelib/io/qsavefile.cpp new file mode 100644 index 0000000000..fee6a4c4d8 --- /dev/null +++ b/src/corelib/io/qsavefile.cpp @@ -0,0 +1,316 @@ +/**************************************************************************** +** +** Copyright (C) 2012 David Faure +** Contact: http://www.qt-project.org/legal +** +** This file is part of the QtCore 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 Digia. For licensing terms and +** conditions see http://qt.digia.com/licensing. For further information +** use the contact form at http://qt.digia.com/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 2.1 as published by the Free Software +** Foundation and appearing in the file LICENSE.LGPL included in the +** packaging of this file. Please review the following information to +** ensure the GNU Lesser General Public License version 2.1 requirements +** will be met: http://www.gnu.org/licenses/old-licenses/lgpl-2.1.html. +** +** In addition, as a special exception, Digia gives you certain additional +** rights. These rights are described in the Digia Qt LGPL Exception +** version 1.1, included in the file LGPL_EXCEPTION.txt in this package. +** +** GNU General Public License Usage +** Alternatively, this file may be used under the terms of the GNU +** General Public License version 3.0 as published by the Free Software +** Foundation and appearing in the file LICENSE.GPL included in the +** packaging of this file. Please review the following information to +** ensure the GNU General Public License version 3.0 requirements will be +** met: http://www.gnu.org/copyleft/gpl.html. +** +** +** $QT_END_LICENSE$ +** +****************************************************************************/ + +#include "qplatformdefs.h" +#include "qsavefile.h" +#include "private/qsavefile_p.h" +#include "qfileinfo.h" +#include "qabstractfileengine_p.h" +#include "qdebug.h" +#include "qtemporaryfile.h" +#include "private/qiodevice_p.h" +#include "private/qtemporaryfile_p.h" + +QT_BEGIN_NAMESPACE + +QSaveFilePrivate::QSaveFilePrivate() + : writeError(QFileDevice::NoError) +{ +} + +QSaveFilePrivate::~QSaveFilePrivate() +{ +} + +/*! + \class QSaveFile + \inmodule QtCore + \brief The QSaveFile class provides an interface for safely writing to files. + + \ingroup io + + \reentrant + + \since 5.1 + + QSaveFile is an I/O device for writing text and binary files, without losing + existing data if the writing operation fails. + + While writing, the contents will be written to a temporary file, and if + no error happened, commit() will move it to the final file. This ensures that + no data at the final file is lost in case an error happens while writing, + and no partially-written file is ever present at the final location. Always + use QSaveFile when saving entire documents to disk. + + QSaveFile automatically detects errors while writing, such as the full partition + situation, where write() cannot write all the bytes. It will remember that + an error happened, and will discard the temporary file in commit(). + + Much like with QFile, the file is opened with open(). Data is usually read + and written using QDataStream or QTextStream, but you can also call the + QIODevice-inherited functions read(), readLine(), readAll(), write(). + + Unlike QFile, calling close() is not allowed. commit() replaces it. If commit() + was not called and the QSaveFile instance is destroyed, the temporary file is + discarded. + + To abort saving due to an application error, call cancelWriting(), so that + even a call to commit() later on will not save. + + \sa QTextStream, QDataStream, QFileInfo, QDir, QFile, QTemporaryFile +*/ + +/*! + Constructs a new file object with the given \a parent. +*/ +QSaveFile::QSaveFile(QObject *parent) + : QFileDevice(*new QSaveFilePrivate, parent) +{ +} +/*! + Constructs a new file object to represent the file with the given \a name. +*/ +QSaveFile::QSaveFile(const QString &name) + : QFileDevice(*new QSaveFilePrivate, 0) +{ + Q_D(QSaveFile); + d->fileName = name; +} +/*! + Constructs a new file object with the given \a parent to represent the + file with the specified \a name. +*/ +QSaveFile::QSaveFile(const QString &name, QObject *parent) + : QFileDevice(*new QSaveFilePrivate, parent) +{ + Q_D(QSaveFile); + d->fileName = name; +} + +/*! + Destroys the file object, discarding the saved contents unless commit() was called. +*/ +QSaveFile::~QSaveFile() +{ + Q_D(QSaveFile); + QFileDevice::close(); + if (d->fileEngine) { + d->fileEngine->remove(); + delete d->fileEngine; + d->fileEngine = 0; + } +} + +/*! + Returns the name set by setFileName() or to the QSaveFile + constructor. + + \sa setFileName() +*/ +QString QSaveFile::fileName() const +{ + return d_func()->fileName; +} + +/*! + Sets the \a name of the file. The name can have no path, a + relative path, or an absolute path. + + \sa QFile::setFileName(), fileName() +*/ +void QSaveFile::setFileName(const QString &name) +{ + d_func()->fileName = name; +} + +/*! + Opens the file using OpenMode \a mode, returning true if successful; + otherwise false. + + Important: the \a mode must include QIODevice::WriteOnly. + It may also have additional flags, such as QIODevice::Text and QIODevice::Unbuffered. + + QIODevice::ReadWrite and QIODevice::Append are not supported at the moment. + + \sa QIODevice::OpenMode, setFileName() +*/ +bool QSaveFile::open(OpenMode mode) +{ + Q_D(QSaveFile); + if (isOpen()) { + qWarning("QSaveFile::open: File (%s) already open", qPrintable(fileName())); + return false; + } + unsetError(); + if ((mode & (ReadOnly | WriteOnly)) == 0) { + qWarning("QSaveFile::open: Open mode not specified"); + return false; + } + // In the future we could implement ReadWrite by copying from the existing file to the temp file... + if ((mode & ReadOnly) || (mode & Append)) { + qWarning("QSaveFile::open: Unsupported open mode 0x%x", int(mode)); + return false; + } + + // check if existing file is writable + QFileInfo existingFile(d->fileName); + if (existingFile.exists() && !existingFile.isWritable()) { + d->setError(QFileDevice::WriteError, QSaveFile::tr("Existing file %1 is not writable").arg(d->fileName)); + d->writeError = QFileDevice::WriteError; + return false; + } + d->fileEngine = new QTemporaryFileEngine(d->fileName); + // Same as in QFile: QIODevice provides the buffering, so there's no need to request it from the file engine. + if (!d->fileEngine->open(mode | QIODevice::Unbuffered)) { + QFileDevice::FileError err = d->fileEngine->error(); + if (err == QFileDevice::UnspecifiedError) + err = QFileDevice::OpenError; + d->setError(err, d->fileEngine->errorString()); + delete d->fileEngine; + d->fileEngine = 0; + return false; + } + + QFileDevice::open(mode); + if (existingFile.exists()) + setPermissions(existingFile.permissions()); + return true; +} + +/*! + \reimp + This method has been made private so that it cannot be called, in order to prevent mistakes. + In order to finish writing the file, call commit(). + If instead you want to abort writing, call cancelWriting(). +*/ +void QSaveFile::close() +{ + qFatal("QSaveFile::close called"); +} + +/*! + Commits the changes to disk, if all previous writes were successful. + + It is mandatory to call this at the end of the saving operation, otherwise the file will be + discarded. + + If an error happened during writing, deletes the temporary file and returns false. + Otherwise, renames it to the final fileName and returns true on success. + Finally, closes the device. + + \sa cancelWriting() +*/ +bool QSaveFile::commit() +{ + Q_D(QSaveFile); + if (!d->fileEngine) + return false; + + if (!isOpen()) { + qWarning("QSaveFile::commit: File (%s) is not open", qPrintable(fileName())); + return false; + } + QFileDevice::close(); // calls flush() + + // Sync to disk if possible. Ignore errors (e.g. not supported). + d->fileEngine->syncToDisk(); + + if (d->writeError != QFileDevice::NoError) { + d->fileEngine->remove(); + d->writeError = QFileDevice::NoError; + delete d->fileEngine; + d->fileEngine = 0; + return false; + } + // atomically replace old file with new file + // Can't use QFile::rename for that, must use the file engine directly + Q_ASSERT(d->fileEngine); + if (!d->fileEngine->renameOverwrite(d->fileName)) { + d->setError(d->fileEngine->error(), d->fileEngine->errorString()); + d->fileEngine->remove(); + delete d->fileEngine; + d->fileEngine = 0; + return false; + } + delete d->fileEngine; + d->fileEngine = 0; + return true; +} + +/*! + Cancels writing the new file. + + If the application changes its mind while saving, it can call cancelWriting(), + which sets an error code so that commit() will discard the temporary file. + + Alternatively, it can simply make sure not to call commit(). + + Further write operations are possible after calling this method, but none + of it will have any effect, the written file will be discarded. + + \sa commit() +*/ +void QSaveFile::cancelWriting() +{ + Q_D(QSaveFile); + if (!isOpen()) + return; + d->setError(QFileDevice::WriteError, QSaveFile::tr("Writing canceled by application")); + d->writeError = QFileDevice::WriteError; +} + +/*! + \reimp +*/ +qint64 QSaveFile::writeData(const char *data, qint64 len) +{ + Q_D(QSaveFile); + if (d->writeError != QFileDevice::NoError) + return -1; + + const qint64 ret = QFileDevice::writeData(data, len); + + if (d->error != QFileDevice::NoError) + d->writeError = d->error; + return ret; +} + +QT_END_NAMESPACE -- cgit v1.2.3