/****************************************************************************
**
** Copyright (C) 2013 David Faure <faure+bluesystems@kde.org>
** Contact: http://www.qt-project.org/legal
**
** This file is part of the QtCore module of the Qt Toolkit.
**
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** General Public License version 2.1 as published by the Free Software
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** ensure the GNU Lesser General Public License version 2.1 requirements
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** 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
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****************************************************************************/

#include "private/qlockfile_p.h"

#include "QtCore/qtemporaryfile.h"
#include "QtCore/qcoreapplication.h"
#include "QtCore/qfileinfo.h"
#include "QtCore/qdebug.h"
#include "QtCore/qdatetime.h"

#include "private/qcore_unix_p.h" // qt_safe_open
#include "private/qabstractfileengine_p.h"
#include "private/qtemporaryfile_p.h"

#include <sys/file.h>  // flock
#include <sys/types.h> // kill
#include <signal.h>    // kill
#include <unistd.h>    // gethostname

QT_BEGIN_NAMESPACE

static QByteArray localHostName() // from QHostInfo::localHostName(), modified to return a QByteArray
{
    QByteArray hostName(512, Qt::Uninitialized);
    if (gethostname(hostName.data(), hostName.size()) == -1)
        return QByteArray();
    hostName.truncate(strlen(hostName.data()));
    return hostName;
}

// ### merge into qt_safe_write?
static qint64 qt_write_loop(int fd, const char *data, qint64 len)
{
    qint64 pos = 0;
    while (pos < len) {
        const qint64 ret = qt_safe_write(fd, data + pos, len - pos);
        if (ret == -1) // e.g. partition full
            return pos;
        pos += ret;
    }
    return pos;
}

int QLockFilePrivate::checkFcntlWorksAfterFlock()
{
#ifndef QT_NO_TEMPORARYFILE
    QTemporaryFile file;
    if (!file.open())
        return 0;
    const int fd = file.d_func()->engine()->handle();
#if defined(LOCK_EX) && defined(LOCK_NB)
    if (flock(fd, LOCK_EX | LOCK_NB) == -1) // other threads, and other processes on a local fs
        return 0;
#endif
    struct flock flockData;
    flockData.l_type = F_WRLCK;
    flockData.l_whence = SEEK_SET;
    flockData.l_start = 0;
    flockData.l_len = 0; // 0 = entire file
    flockData.l_pid = getpid();
    if (fcntl(fd, F_SETLK, &flockData) == -1) // for networked filesystems
        return 0;
    return 1;
#else
    return 0;
#endif
}

static QBasicAtomicInt fcntlOK = Q_BASIC_ATOMIC_INITIALIZER(-1);

/*!
  \internal
  Checks that the OS isn't using POSIX locks to emulate flock().
  Mac OS X is one of those.
*/
static bool fcntlWorksAfterFlock()
{
    int value = fcntlOK.load();
    if (Q_UNLIKELY(value == -1)) {
        value = QLockFilePrivate::checkFcntlWorksAfterFlock();
        fcntlOK.store(value);
    }
    return value == 1;
}

static bool setNativeLocks(int fd)
{
#if defined(LOCK_EX) && defined(LOCK_NB)
    if (flock(fd, LOCK_EX | LOCK_NB) == -1) // other threads, and other processes on a local fs
        return false;
#endif
    struct flock flockData;
    flockData.l_type = F_WRLCK;
    flockData.l_whence = SEEK_SET;
    flockData.l_start = 0;
    flockData.l_len = 0; // 0 = entire file
    flockData.l_pid = getpid();
    if (fcntlWorksAfterFlock() && fcntl(fd, F_SETLK, &flockData) == -1) // for networked filesystems
        return false;
    return true;
}

QLockFile::LockError QLockFilePrivate::tryLock_sys()
{
    // Assemble data, to write in a single call to write
    // (otherwise we'd have to check every write call)
    // Use operator% from the fast builder to avoid multiple memory allocations.
    QByteArray fileData = QByteArray::number(QCoreApplication::applicationPid()) % '\n'
                          % qAppName().toUtf8() % '\n'
                          % localHostName() % '\n';

    const QByteArray lockFileName = QFile::encodeName(fileName);
    const int fd = qt_safe_open(lockFileName.constData(), O_WRONLY | O_CREAT | O_EXCL, 0644);
    if (fd < 0) {
        switch (errno) {
        case EEXIST:
            return QLockFile::LockFailedError;
        case EACCES:
        case EROFS:
            return QLockFile::PermissionError;
        default:
            return QLockFile::UnknownError;
        }
    }
    // Ensure nobody else can delete the file while we have it
    if (!setNativeLocks(fd))
        qWarning() << "setNativeLocks failed:" << strerror(errno);

    // We hold the lock, continue.
    fileHandle = fd;

    QLockFile::LockError error = QLockFile::NoError;
    if (qt_write_loop(fd, fileData.constData(), fileData.size()) < fileData.size())
        error = QLockFile::UnknownError; // partition full
    return error;
}

bool QLockFilePrivate::removeStaleLock()
{
    const QByteArray lockFileName = QFile::encodeName(fileName);
    const int fd = qt_safe_open(lockFileName.constData(), O_WRONLY, 0644);
    if (fd < 0) // gone already?
        return false;
    bool success = setNativeLocks(fd) && (::unlink(lockFileName) == 0);
    close(fd);
    return success;
}

bool QLockFilePrivate::isApparentlyStale() const
{
    qint64 pid;
    QString hostname, appname;
    if (!getLockInfo(&pid, &hostname, &appname))
        return false;
    if (hostname == QString::fromLocal8Bit(localHostName())) {
        if (::kill(pid, 0) == -1 && errno == ESRCH)
            return true; // PID doesn't exist anymore
    }
    const qint64 age = QFileInfo(fileName).lastModified().msecsTo(QDateTime::currentDateTime());
    return staleLockTime > 0 && age > staleLockTime;
}

void QLockFile::unlock()
{
    Q_D(QLockFile);
    if (!d->isLocked)
        return;
    close(d->fileHandle);
    d->fileHandle = -1;
    QFile::remove(d->fileName);
    d->lockError = QLockFile::NoError;
    d->isLocked = false;
}

QT_END_NAMESPACE