qtemporaryfile.cpp

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// Copyright (C) 2016 The Qt Company Ltd.
// Copyright (C) 2017 Intel Corporation.
// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR LGPL-3.0-only OR GPL-2.0-only OR GPL-3.0-only
 
#include "qtemporaryfile.h"
 
#include "qplatformdefs.h"
#include "qrandom.h"
#include "private/qtemporaryfile_p.h"
#include "private/qfile_p.h"
#include "private/qsystemerror_p.h"
 
#if !defined(Q_OS_WIN)
#include "private/qcore_unix_p.h"       // overrides QT_OPEN
#include <errno.h>
#endif
 
#if defined(QT_BUILD_CORE_LIB)
#include "qcoreapplication.h"
#else
#define tr(X) QString::fromLatin1(X)
#endif
 
QT_BEGIN_NAMESPACE
 
using namespace Qt::StringLiterals;
 
#if defined(Q_OS_WIN)
typedef ushort Char;
 
static inline Char Latin1Char(char ch)
{
    return ushort(uchar(ch));
}
 
typedef HANDLE NativeFileHandle;
 
#else // POSIX
typedef char Char;
typedef char Latin1Char;
typedef int NativeFileHandle;
#endif
 
QTemporaryFileName::QTemporaryFileName(const QString &templateName)
{
    // Ensure there is a placeholder mask
    QString qfilename = QDir::fromNativeSeparators(templateName);
    qsizetype phPos = qfilename.size();
    qsizetype phLength = 0;
 
    while (phPos != 0) {
        --phPos;
 
        if (qfilename[phPos] == u'X') {
            ++phLength;
            continue;
        }
 
        if (phLength >= 6
                || qfilename[phPos] == u'/') {
            ++phPos;
            break;
        }
 
        // start over
        phLength = 0;
    }
 
    if (phLength < 6)
        qfilename.append(".XXXXXX"_L1);
 
    // "Nativify" :-)
    QFileSystemEntry::NativePath filename = QFileSystemEngine::absoluteName(
            QFileSystemEntry(qfilename, QFileSystemEntry::FromInternalPath()))
        .nativeFilePath();
 
    // Find mask in native path
    phPos = filename.size();
    phLength = 0;
    while (phPos != 0) {
        --phPos;
 
        if (filename[phPos] == Latin1Char('X')) {
            ++phLength;
            continue;
        }
 
        if (phLength >= 6) {
            ++phPos;
            break;
        }
 
        // start over
        phLength = 0;
    }
 
    Q_ASSERT(phLength >= 6);
    path = filename;
    pos = phPos;
    length = phLength;
}
 
QFileSystemEntry::NativePath QTemporaryFileName::generateNext()
{
    Q_ASSERT(length != 0);
    Q_ASSERT(pos < path.size());
    Q_ASSERT(length <= path.size() - pos);
 
    Char *const placeholderStart = (Char *)path.data() + pos;
    Char *const placeholderEnd = placeholderStart + length;
 
    // Replace placeholder with random chars.
    {
        // Since our dictionary is 26+26 characters, it would seem we only need
        // a random number from 0 to 63 to select a character. However, due to
        // the limited range, that would mean 12 (64-52) characters have double
        // the probability of the others: 1 in 32 instead of 1 in 64.
        //
        // To overcome this limitation, we use more bits per character. With 10
        // bits, there are 16 characters with probability 19/1024 and the rest
        // at 20/1024 (i.e, less than .1% difference). This allows us to do 3
        // characters per 32-bit random number, which is also half the typical
        // placeholder length.
        enum { BitsPerCharacter = 10 };
 
        Char *rIter = placeholderEnd;
        while (rIter != placeholderStart) {
            quint32 rnd = QRandomGenerator::global()->generate();
            auto applyOne = [&]() {
                quint32 v = rnd & ((1 << BitsPerCharacter) - 1);
                rnd >>= BitsPerCharacter;
                char ch = char((26 + 26) * v / (1 << BitsPerCharacter));
                if (ch < 26)
                    *--rIter = Latin1Char(ch + 'A');
                else
                    *--rIter = Latin1Char(ch - 26 + 'a');
            };
 
            applyOne();
            if (rIter == placeholderStart)
                break;
 
            applyOne();
            if (rIter == placeholderStart)
                break;
 
            applyOne();
        }
    }
 
    return path;
}
 
#ifndef QT_NO_TEMPORARYFILE
 
static bool createFileFromTemplate(NativeFileHandle &file, QTemporaryFileName &templ,
                                   quint32 mode, int flags, QSystemError &error)
{
    const int maxAttempts = 16;
    for (int attempt = 0; attempt < maxAttempts; ++attempt) {
        // Atomically create file and obtain handle
        const QFileSystemEntry::NativePath &path = templ.generateNext();
 
#if defined(Q_OS_WIN)
        Q_UNUSED(mode);
        const DWORD shareMode = (flags & QTemporaryFileEngine::Win32NonShared)
                                ? 0u : (FILE_SHARE_READ | FILE_SHARE_WRITE);
 
        file = CreateFile((const wchar_t *)path.constData(),
                GENERIC_READ | GENERIC_WRITE,
                shareMode, NULL, CREATE_NEW,
                FILE_ATTRIBUTE_NORMAL, NULL);
 
        if (file != INVALID_HANDLE_VALUE)
            return true;
 
        DWORD err = GetLastError();
        if (err == ERROR_ACCESS_DENIED) {
            WIN32_FILE_ATTRIBUTE_DATA attributes;
            if (!GetFileAttributesEx((const wchar_t *)path.constData(),
                                     GetFileExInfoStandard, &attributes)
                    || attributes.dwFileAttributes == INVALID_FILE_ATTRIBUTES) {
                // Potential write error (read-only parent directory, etc.).
                error = QSystemError(err, QSystemError::NativeError);
                return false;
            } // else file already exists as a directory.
        } else if (err != ERROR_FILE_EXISTS) {
            error = QSystemError(err, QSystemError::NativeError);
            return false;
        }
#else // POSIX
        Q_UNUSED(flags);
        file = QT_OPEN(path.constData(),
                QT_OPEN_CREAT | QT_OPEN_EXCL | QT_OPEN_RDWR | QT_OPEN_LARGEFILE,
                static_cast<mode_t>(mode));
 
        if (file != -1)
            return true;
 
        int err = errno;
        if (err != EEXIST) {
            error = QSystemError(err, QSystemError::NativeError);
            return false;
        }
#endif
    }
 
    return false;
}
 
enum class CreateUnnamedFileStatus {
    Success = 0,
    NotSupported,
    OtherError
};
 
static CreateUnnamedFileStatus
createUnnamedFile(NativeFileHandle &file, QTemporaryFileName &tfn, quint32 mode, QSystemError *error)
{
#ifdef LINUX_UNNAMED_TMPFILE
    // first, check if we have /proc, otherwise can't make the file exist later
    // (no error message set, as caller will try regular temporary file)
    if (!qt_haveLinuxProcfs())
        return CreateUnnamedFileStatus::NotSupported;
 
    const char *p = ".";
    QByteArray::size_type lastSlash = tfn.path.lastIndexOf('/');
    if (lastSlash >= 0) {
        if (lastSlash == 0)
            lastSlash = 1;
        tfn.path[lastSlash] = '\0';
        p = tfn.path.data();
    }
 
    file = QT_OPEN(p, O_TMPFILE | QT_OPEN_RDWR | QT_OPEN_LARGEFILE,
            static_cast<mode_t>(mode));
    if (file != -1)
        return CreateUnnamedFileStatus::Success;
 
    if (errno == EOPNOTSUPP || errno == EISDIR) {
        // fs or kernel doesn't support O_TMPFILE, so
        // put the slash back so we may try a regular file
        if (lastSlash != -1)
            tfn.path[lastSlash] = '/';
        return CreateUnnamedFileStatus::NotSupported;
    }
 
    // real error
    *error = QSystemError(errno, QSystemError::NativeError);
    return CreateUnnamedFileStatus::OtherError;
#else
    Q_UNUSED(file);
    Q_UNUSED(tfn);
    Q_UNUSED(mode);
    Q_UNUSED(error);
    return CreateUnnamedFileStatus::NotSupported;
#endif
}
 
//************* QTemporaryFileEngine
QTemporaryFileEngine::~QTemporaryFileEngine()
{
    Q_D(QFSFileEngine);
    d->unmapAll();
    QFSFileEngine::close();
}
 
bool QTemporaryFileEngine::isReallyOpen() const
{
    Q_D(const QFSFileEngine);
 
    if (!((nullptr == d->fh) && (-1 == d->fd)
#if defined Q_OS_WIN
                && (INVALID_HANDLE_VALUE == d->fileHandle)
#endif
            ))
        return true;
 
    return false;
 
}
 
void QTemporaryFileEngine::setFileName(const QString &file)
{
    // Really close the file, so we don't leak
    QFSFileEngine::close();
    QFSFileEngine::setFileName(file);
}
 
bool QTemporaryFileEngine::open(QIODevice::OpenMode openMode,
                                std::optional<QFile::Permissions> permissions)
{
    Q_D(QFSFileEngine);
    Q_ASSERT(!isReallyOpen());
 
    openMode |= QIODevice::ReadWrite;
 
    if (!filePathIsTemplate)
        return QFSFileEngine::open(openMode, permissions);
 
    QTemporaryFileName tfn(templateName);
 
    QSystemError error;
#if defined(Q_OS_WIN)
    NativeFileHandle &file = d->fileHandle;
#else // POSIX
    NativeFileHandle &file = d->fd;
#endif
 
    CreateUnnamedFileStatus st = createUnnamedFile(file, tfn, fileMode, &error);
    if (st == CreateUnnamedFileStatus::Success) {
        unnamedFile = true;
        d->fileEntry.clear();
    } else if (st == CreateUnnamedFileStatus::NotSupported &&
               createFileFromTemplate(file, tfn, fileMode, flags, error)) {
        filePathIsTemplate = false;
        unnamedFile = false;
        d->fileEntry = QFileSystemEntry(tfn.path, QFileSystemEntry::FromNativePath());
    } else {
        setError(QFile::OpenError, error.toString());
        return false;
    }
 
#if !defined(Q_OS_WIN)
    d->closeFileHandle = true;
#endif
 
    d->openMode = openMode;
    d->lastFlushFailed = false;
    d->tried_stat = 0;
 
    return true;
}
 
bool QTemporaryFileEngine::remove()
{
    Q_D(QFSFileEngine);
    // Since the QTemporaryFileEngine::close() does not really close the file,
    // we must explicitly call QFSFileEngine::close() before we remove it.
    d->unmapAll();
    QFSFileEngine::close();
    if (isUnnamedFile())
        return true;
    if (!filePathIsTemplate && QFSFileEngine::remove()) {
        d->fileEntry.clear();
        // If a QTemporaryFile is constructed using a template file path, the path
        // is generated in QTemporaryFileEngine::open() and then filePathIsTemplate
        // is set to false. If remove() and then open() are called on the same
        // QTemporaryFile, the path is not regenerated. Here we ensure that if the
        // file path was generated, it will be generated again in the scenario above.
        filePathIsTemplate = filePathWasTemplate;
        return true;
    }
    return false;
}
 
bool QTemporaryFileEngine::rename(const QString &newName)
{
    if (isUnnamedFile()) {
        bool ok = materializeUnnamedFile(newName, DontOverwrite);
        QFSFileEngine::close();
        return ok;
    }
    QFSFileEngine::close();
    return QFSFileEngine::rename(newName);
}
 
bool QTemporaryFileEngine::renameOverwrite(const QString &newName)
{
    if (isUnnamedFile()) {
        bool ok = materializeUnnamedFile(newName, Overwrite);
        QFSFileEngine::close();
        return ok;
    }
    QFSFileEngine::close();
    return QFSFileEngine::renameOverwrite(newName);
}
 
bool QTemporaryFileEngine::close()
{
    // Don't close the file, just seek to the front.
    seek(0);
    setError(QFile::UnspecifiedError, QString());
    return true;
}
 
QString QTemporaryFileEngine::fileName(QAbstractFileEngine::FileName file) const
{
    if (isUnnamedFile()) {
        if (file == AbsoluteLinkTarget || file == RawLinkPath) {
            // we know our file isn't (won't be) a symlink
            return QString();
        }
 
        // for all other cases, materialize the file
        const_cast<QTemporaryFileEngine *>(this)->materializeUnnamedFile(templateName, NameIsTemplate);
    }
    return QFSFileEngine::fileName(file);
}
 
bool QTemporaryFileEngine::materializeUnnamedFile(const QString &newName, QTemporaryFileEngine::MaterializationMode mode)
{
    Q_ASSERT(isUnnamedFile());
 
#ifdef LINUX_UNNAMED_TMPFILE
    Q_D(QFSFileEngine);
    const QByteArray src = "/proc/self/fd/" + QByteArray::number(d->fd);
    auto materializeAt = [=](const QFileSystemEntry &dst) {
        return ::linkat(AT_FDCWD, src, AT_FDCWD, dst.nativeFilePath(), AT_SYMLINK_FOLLOW) == 0;
    };
#else
    auto materializeAt = [](const QFileSystemEntry &) { return false; };
#endif
 
    auto success = [this](const QFileSystemEntry &entry) {
        filePathIsTemplate = false;
        unnamedFile = false;
        d_func()->fileEntry = entry;
        return true;
    };
 
    auto materializeAsTemplate = [=](const QString &newName) {
        QTemporaryFileName tfn(newName);
        static const int maxAttempts = 16;
        for (int attempt = 0; attempt < maxAttempts; ++attempt) {
            tfn.generateNext();
            QFileSystemEntry entry(tfn.path, QFileSystemEntry::FromNativePath());
            if (materializeAt(entry))
                return success(entry);
        }
        return false;
    };
 
    if (mode == NameIsTemplate) {
        if (materializeAsTemplate(newName))
            return true;
    } else {
        // Use linkat to materialize the file
        QFileSystemEntry dst(newName);
        if (materializeAt(dst))
            return success(dst);
 
        if (errno == EEXIST && mode == Overwrite) {
            // retry by first creating a temporary file in the right dir
            if (!materializeAsTemplate(templateName))
                return false;
 
            // then rename the materialized file to target (same as renameOverwrite)
            QFSFileEngine::close();
            return QFSFileEngine::renameOverwrite(newName);
        }
    }
 
    // failed
    setError(QFile::RenameError, QSystemError(errno, QSystemError::NativeError).toString());
    return false;
}
 
bool QTemporaryFileEngine::isUnnamedFile() const
{
#ifdef LINUX_UNNAMED_TMPFILE
    if (unnamedFile) {
        Q_ASSERT(d_func()->fileEntry.isEmpty());
        Q_ASSERT(filePathIsTemplate);
    }
    return unnamedFile;
#else
    return false;
#endif
}
 
//************* QTemporaryFilePrivate
 
QTemporaryFilePrivate::QTemporaryFilePrivate()
{
}
 
QTemporaryFilePrivate::QTemporaryFilePrivate(const QString &templateNameIn)
    : templateName(templateNameIn)
{
}
 
QTemporaryFilePrivate::~QTemporaryFilePrivate()
{
}
 
QAbstractFileEngine *QTemporaryFilePrivate::engine() const
{
    if (!fileEngine) {
        fileEngine.reset(new QTemporaryFileEngine(&templateName));
        resetFileEngine();
    }
    return fileEngine.get();
}
 
void QTemporaryFilePrivate::resetFileEngine() const
{
    if (!fileEngine)
        return;
 
    QTemporaryFileEngine *tef = static_cast<QTemporaryFileEngine *>(fileEngine.get());
    if (fileName.isEmpty())
        tef->initialize(templateName, 0600);
    else
        tef->initialize(fileName, 0600, false);
}
 
void QTemporaryFilePrivate::materializeUnnamedFile()
{
#ifdef LINUX_UNNAMED_TMPFILE
    if (!fileName.isEmpty() || !fileEngine)
        return;
 
    auto *tef = static_cast<QTemporaryFileEngine *>(fileEngine.get());
    fileName = tef->fileName(QAbstractFileEngine::DefaultName);
#endif
}
 
QString QTemporaryFilePrivate::defaultTemplateName()
{
    QString baseName;
#if defined(QT_BUILD_CORE_LIB)
    baseName = QCoreApplication::applicationName();
    if (baseName.isEmpty())
#endif
        baseName = "qt_temp"_L1;
 
    return QDir::tempPath() + u'/' + baseName + ".XXXXXX"_L1;
}
 
//************* QTemporaryFile
 
#ifdef QT_NO_QOBJECT
QTemporaryFile::QTemporaryFile()
    : QFile(*new QTemporaryFilePrivate)
{
}
 
QTemporaryFile::QTemporaryFile(const QString &templateName)
    : QFile(*new QTemporaryFilePrivate(templateName))
{
}
 
#else
QTemporaryFile::QTemporaryFile()
    : QTemporaryFile(nullptr)
{
}
 
QTemporaryFile::QTemporaryFile(const QString &templateName)
    : QTemporaryFile(templateName, nullptr)
{
}
 
QTemporaryFile::QTemporaryFile(QObject *parent)
    : QFile(*new QTemporaryFilePrivate, parent)
{
}
 
QTemporaryFile::QTemporaryFile(const QString &templateName, QObject *parent)
    : QFile(*new QTemporaryFilePrivate(templateName), parent)
{
}
#endif
 
QTemporaryFile::~QTemporaryFile()
{
    Q_D(QTemporaryFile);
    close();
    if (!d->fileName.isEmpty() && d->autoRemove)
        remove();
}
 
bool QTemporaryFile::autoRemove() const
{
    Q_D(const QTemporaryFile);
    return d->autoRemove;
}
 
void QTemporaryFile::setAutoRemove(bool b)
{
    Q_D(QTemporaryFile);
    d->autoRemove = b;
}
 
QString QTemporaryFile::fileName() const
{
    Q_D(const QTemporaryFile);
    auto tef = static_cast<QTemporaryFileEngine *>(d->fileEngine.get());
    if (tef && tef->isReallyOpen())
        const_cast<QTemporaryFilePrivate *>(d)->materializeUnnamedFile();
 
    if (d->fileName.isEmpty())
        return QString();
    return d->engine()->fileName(QAbstractFileEngine::DefaultName);
}
 
QString QTemporaryFile::fileTemplate() const
{
    Q_D(const QTemporaryFile);
    return d->templateName;
}
 
void QTemporaryFile::setFileTemplate(const QString &name)
{
    Q_D(QTemporaryFile);
    d->templateName = name;
}
 
bool QTemporaryFile::rename(const QString &newName)
{
    Q_D(QTemporaryFile);
    auto tef = static_cast<QTemporaryFileEngine *>(d->fileEngine.get());
    if (!tef || !tef->isReallyOpen() || !tef->filePathWasTemplate)
        return QFile::rename(newName);
 
    unsetError();
    close();
    if (error() == QFile::NoError) {
        if (tef->rename(newName)) {
            unsetError();
            // engine was able to handle the new name so we just reset it
            tef->setFileName(newName);
            d->fileName = newName;
            return true;
        }
 
        d->setError(QFile::RenameError, tef->errorString());
    }
    return false;
}
 
QTemporaryFile *QTemporaryFile::createNativeFile(QFile &file)
{
    if (QAbstractFileEngine *engine = file.d_func()->engine()) {
        if (engine->fileFlags(QAbstractFileEngine::FlagsMask) & QAbstractFileEngine::LocalDiskFlag)
            return nullptr; // native already
        //cache
        bool wasOpen = file.isOpen();
        qint64 old_off = 0;
        if (wasOpen)
            old_off = file.pos();
        else if (!file.open(QIODevice::ReadOnly))
            return nullptr;
        //dump data
        QTemporaryFile *ret = new QTemporaryFile;
        if (ret->open()) {
            file.seek(0);
            char buffer[1024];
            while (true) {
                qint64 len = file.read(buffer, 1024);
                if (len < 1)
                    break;
                ret->write(buffer, len);
            }
            ret->seek(0);
        } else {
            delete ret;
            ret = nullptr;
        }
        //restore
        if (wasOpen)
            file.seek(old_off);
        else
            file.close();
        //done
        return ret;
    }
    return nullptr;
}
 
bool QTemporaryFile::open(OpenMode flags)
{
    Q_D(QTemporaryFile);
    auto tef = static_cast<QTemporaryFileEngine *>(d->fileEngine.get());
    if (tef && tef->isReallyOpen()) {
        setOpenMode(flags);
        return true;
    }
 
    // reset the engine state so it creates a new, unique file name from the template;
    // equivalent to:
    //    delete d->fileEngine;
    //    d->fileEngine = 0;
    //    d->engine();
    d->resetFileEngine();
 
    if (QFile::open(flags)) {
        tef = static_cast<QTemporaryFileEngine *>(d->fileEngine.get());
        if (tef->isUnnamedFile())
            d->fileName.clear();
        else
            d->fileName = tef->fileName(QAbstractFileEngine::DefaultName);
        return true;
    }
    return false;
}
 
#endif // QT_NO_TEMPORARYFILE
 
QT_END_NAMESPACE
 
#ifndef QT_NO_QOBJECT
#include "moc_qtemporaryfile.cpp"
#endif