diff -r 6aeb7a756187 -r 3c88a81ff781 browsercore/core/network/featherweightcache.cpp
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/browsercore/core/network/featherweightcache.cpp	Fri Oct 15 17:30:59 2010 -0400
@@ -0,0 +1,924 @@
+/****************************************************************************
+**
+ * Copyright (c) 2010 Nokia Corporation and/or its subsidiary(-ies).
+ *
+ * This file is part of Qt Web Runtime.
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public License
+ * version 2.1 as published by the Free Software Foundation.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ */
+
+# include <QAbstractNetworkCache>
+# include <QNetworkCacheMetaData>
+# include <QDateTime>
+# include <QDir>
+# include <QDirIterator>
+# include <QFile>
+# include <QtGlobal>
+# include <QDebug>
+# include <QQueue>
+# include <featherweightcache.h>
+# include <featherweightcache_p.h>
+#if defined(Q_OS_SYMBIAN)
+#include <e32std.h>
+#endif
+
+//#define FEATHERWEIGHTCACHE_DEBUG
+
+#define CACHE_POSTFIX QLatin1String(".d")
+#define PREPARED_SLASH QLatin1String("prepared/")
+#define DATA_SLASH QLatin1String("data/")
+#define MAX_COMPRESSION_SIZE (1024 * 1024 * 3)
+
+namespace WRT {
+
+/*!
+    \class FeatherWeightCache
+
+    \brief The FeatherWeightCache class provides a very basic disk cache.
+
+    FeatherWeightCache stores each url in its own file inside of the
+    cacheDirectory using QDataStream.  Files with a text MimeType
+    are compressed using qCompress.  Each cache file starts with "cache_"
+    and ends in ".cache".  Data is written to disk only in insert()
+    and updateMetaData().
+
+    Currently you can not share the same cache files with more then
+    one disk cache.
+
+    FeatherWeightCache by default limits the amount of space that the cache will
+    use on the system to 50MB.
+
+    Note you have to set the cache directory before it will work.
+
+    A network disk cache can be enabled by:
+
+    \snippet doc/src/snippets/code/src_network_access_FeatherWeightCache.cpp 0
+
+    When sending requests, to control the preference of when to use the cache
+    and when to use the network, consider the following:
+
+    \snippet doc/src/snippets/code/src_network_access_FeatherWeightCache.cpp 1
+
+    To check whether the response came from the cache or from the network, the
+    following can be applied:
+
+    \snippet doc/src/snippets/code/src_network_access_FeatherWeightCache.cpp 2
+*/
+
+/*!
+    Creates a new disk cache. The \a parent argument is passed to
+    QAbstractNetworkCache's constructor.
+ */
+FeatherWeightCache::FeatherWeightCache(QObject *parent)
+    : QAbstractNetworkCache(parent)
+{
+
+    d = new FeatherWeightCachePrivate(this);
+}
+
+/*!
+    Destroys the cache object.  This does not clear the disk cache.
+ */
+FeatherWeightCache::~FeatherWeightCache()
+{
+    QHashIterator<QIODevice*, CacheItem*> it(d->inserting);
+    while (it.hasNext()) {
+        it.next();
+        delete it.value();
+    }
+
+}
+
+/*!
+    Returns the location where cached files will be stored.
+*/
+QString FeatherWeightCache::cacheDirectory() const
+{
+    return d->cacheDirectory;
+}
+
+/*!
+    Sets the directory where cached files will be stored to \a cacheDir
+
+    FeatherWeightCache will create this directory if it does not exists.
+
+    Prepared cache items will be stored in the new cache directory when
+    they are inserted.
+
+    \sa QDesktopServices::CacheLocation
+*/
+void FeatherWeightCache::setCacheDirectory(const QString &cacheDir)
+{
+#if defined(FEATHERWEIGHTCACHE_DEBUG)
+    qDebug() << "FeatherWeightCache::setCacheDirectory()" << cacheDir;
+#endif
+    if (cacheDir.isEmpty())
+        return;
+    d->cacheDirectory = cacheDir;
+    QDir dir(d->cacheDirectory);
+    d->cacheDirectory = dir.absolutePath();
+    if (!d->cacheDirectory.endsWith(QLatin1Char('/')))
+        d->cacheDirectory += QLatin1Char('/');
+
+    d->prepareLayout();
+}
+
+/*!
+    \reimp
+*/
+qint64 FeatherWeightCache::cacheSize() const
+{
+#if defined(FEATHERWEIGHTCACHE_DEBUG)
+    qDebug() << "FeatherWeightCache::cacheSize()";
+#endif
+    if (d->cacheDirectory.isEmpty())
+        return 0;
+    if (d->currentCacheSize < 0) {
+        FeatherWeightCache *that = const_cast<FeatherWeightCache*>(this);
+        that->d->currentCacheSize = that->expire();
+    }
+    return d->currentCacheSize;
+}
+
+/*!
+    \reimp
+*/
+QIODevice *FeatherWeightCache::prepare(const QNetworkCacheMetaData &metaData)
+{
+#if defined(FEATHERWEIGHTCACHE_DEBUG)
+    //qDebug() << "FeatherWeightCache::prepare()" << metaData.url();
+#endif
+    if (!metaData.isValid() || !metaData.url().isValid() || !metaData.saveToDisk())
+        return 0;
+
+    if (d->cacheDirectory.isEmpty()) {
+        qWarning() << "FeatherWeightCache::prepare() The cache directory is not set";
+        return 0;
+    }
+
+    foreach (QNetworkCacheMetaData::RawHeader header, metaData.rawHeaders()) {
+        if (header.first.toLower() == "content-length") {
+            qint64 size = header.second.toInt();
+            if (size > (maximumCacheSize() * 3)/4)
+                return 0;
+            break;
+        }
+    }
+    QScopedPointer<CacheItem> cacheItem(new CacheItem);
+    cacheItem->metaData = metaData;
+
+    QIODevice *device = 0;
+    if (cacheItem->canCompress()) {
+        cacheItem->data.open(QBuffer::ReadWrite);
+        device = &(cacheItem->data);
+    } else {
+        QString templateName = d->tmpCacheFileName();
+        QT_TRY {
+            cacheItem->file = new QTemporaryFile(templateName, &cacheItem->data);
+        } QT_CATCH(...) {
+            cacheItem->file = 0;
+        }
+        if (!cacheItem->file || !cacheItem->file->open()) {
+            qWarning() << "FeatherWeightCache::prepare() unable to open temporary file";
+            cacheItem.reset();
+            return 0;
+        }
+        cacheItem->writeHeader(cacheItem->file);
+        device = cacheItem->file;
+    }
+    d->inserting[device] = cacheItem.take();
+    return device;
+}
+
+/*!
+    \reimp
+*/
+void FeatherWeightCache::insert(QIODevice *device)
+{
+#if defined(FEATHERWEIGHTCACHE_DEBUG)
+    //qDebug() << "FeatherWeightCache::insert()" << device;
+#endif
+    QHash<QIODevice*, CacheItem*>::iterator it = d->inserting.find(device);
+    if (it == d->inserting.end()) {
+        qWarning() << "FeatherWeightCache::insert() called on a device we don't know about" << device;
+        return;
+    }
+
+    d->storeItem(it.value());
+    delete it.value();
+    d->inserting.erase(it);
+}
+
+
+/*!
+    Create subdirectories and other housekeeping on the filesystem.
+    Prevents too many files from being present in any single directory.
+*/
+void FeatherWeightCachePrivate::prepareLayout()
+{
+    QDir prepared;
+    prepared.mkpath(cacheDirectory + PREPARED_SLASH);
+
+    QString path = cacheDirectory + DATA_SLASH;
+    QDir dataDirectory(path);
+
+    //Create directory and subdirectories 0-F
+    dataDirectory.mkpath(path);
+    for ( uint i = 0; i < 16 ; i++ ) {
+        QString str = QString::number(i, 16);
+        QString subdir = dataDirectory.path() + QDir::separator() + str;
+        dataDirectory.mkdir(subdir);
+    }
+
+    // TODO: populate volumeInfo members here base on which disk/fileystem
+    // you plan to write (a) temp ("prepared") files to (b) write final cache files too
+    // volumeInfo->clusterSize = 1024;
+    // volumeInfo->readBufSize = 16384;
+    // volumeInfo->writeBufSize = 16384;
+#ifdef Q_OS_SYMBIAN
+    //VolumeIOParam(TInt aDriveNo, TVolumeIOParamInfo &aParamInfo) const;
+#endif
+}
+
+// CRC32 implementation.
+// Could be made into new API QByteArray:qChecksum32()
+static const quint32 crc_tbl32[256] = {
+    0x00000000, 0x77073096, 0xee0e612c, 0x990951ba,
+    0x076dc419, 0x706af48f, 0xe963a535, 0x9e6495a3,
+    0x0edb8832, 0x79dcb8a4, 0xe0d5e91e, 0x97d2d988,
+    0x09b64c2b, 0x7eb17cbd, 0xe7b82d07, 0x90bf1d91,
+    0x1db71064, 0x6ab020f2, 0xf3b97148, 0x84be41de,
+    0x1adad47d, 0x6ddde4eb, 0xf4d4b551, 0x83d385c7,
+    0x136c9856, 0x646ba8c0, 0xfd62f97a, 0x8a65c9ec,
+    0x14015c4f, 0x63066cd9, 0xfa0f3d63, 0x8d080df5,
+    0x3b6e20c8, 0x4c69105e, 0xd56041e4, 0xa2677172,
+    0x3c03e4d1, 0x4b04d447, 0xd20d85fd, 0xa50ab56b,
+    0x35b5a8fa, 0x42b2986c, 0xdbbbc9d6, 0xacbcf940,
+    0x32d86ce3, 0x45df5c75, 0xdcd60dcf, 0xabd13d59,
+    0x26d930ac, 0x51de003a, 0xc8d75180, 0xbfd06116,
+    0x21b4f4b5, 0x56b3c423, 0xcfba9599, 0xb8bda50f,
+    0x2802b89e, 0x5f058808, 0xc60cd9b2, 0xb10be924,
+    0x2f6f7c87, 0x58684c11, 0xc1611dab, 0xb6662d3d,
+    0x76dc4190, 0x01db7106, 0x98d220bc, 0xefd5102a,
+    0x71b18589, 0x06b6b51f, 0x9fbfe4a5, 0xe8b8d433,
+    0x7807c9a2, 0x0f00f934, 0x9609a88e, 0xe10e9818,
+    0x7f6a0dbb, 0x086d3d2d, 0x91646c97, 0xe6635c01,
+    0x6b6b51f4, 0x1c6c6162, 0x856530d8, 0xf262004e,
+    0x6c0695ed, 0x1b01a57b, 0x8208f4c1, 0xf50fc457,
+    0x65b0d9c6, 0x12b7e950, 0x8bbeb8ea, 0xfcb9887c,
+    0x62dd1ddf, 0x15da2d49, 0x8cd37cf3, 0xfbd44c65,
+    0x4db26158, 0x3ab551ce, 0xa3bc0074, 0xd4bb30e2,
+    0x4adfa541, 0x3dd895d7, 0xa4d1c46d, 0xd3d6f4fb,
+    0x4369e96a, 0x346ed9fc, 0xad678846, 0xda60b8d0,
+    0x44042d73, 0x33031de5, 0xaa0a4c5f, 0xdd0d7cc9,
+    0x5005713c, 0x270241aa, 0xbe0b1010, 0xc90c2086,
+    0x5768b525, 0x206f85b3, 0xb966d409, 0xce61e49f,
+    0x5edef90e, 0x29d9c998, 0xb0d09822, 0xc7d7a8b4,
+    0x59b33d17, 0x2eb40d81, 0xb7bd5c3b, 0xc0ba6cad,
+    0xedb88320, 0x9abfb3b6, 0x03b6e20c, 0x74b1d29a,
+    0xead54739, 0x9dd277af, 0x04db2615, 0x73dc1683,
+    0xe3630b12, 0x94643b84, 0x0d6d6a3e, 0x7a6a5aa8,
+    0xe40ecf0b, 0x9309ff9d, 0x0a00ae27, 0x7d079eb1,
+    0xf00f9344, 0x8708a3d2, 0x1e01f268, 0x6906c2fe,
+    0xf762575d, 0x806567cb, 0x196c3671, 0x6e6b06e7,
+    0xfed41b76, 0x89d32be0, 0x10da7a5a, 0x67dd4acc,
+    0xf9b9df6f, 0x8ebeeff9, 0x17b7be43, 0x60b08ed5,
+    0xd6d6a3e8, 0xa1d1937e, 0x38d8c2c4, 0x4fdff252,
+    0xd1bb67f1, 0xa6bc5767, 0x3fb506dd, 0x48b2364b,
+    0xd80d2bda, 0xaf0a1b4c, 0x36034af6, 0x41047a60,
+    0xdf60efc3, 0xa867df55, 0x316e8eef, 0x4669be79,
+    0xcb61b38c, 0xbc66831a, 0x256fd2a0, 0x5268e236,
+    0xcc0c7795, 0xbb0b4703, 0x220216b9, 0x5505262f,
+    0xc5ba3bbe, 0xb2bd0b28, 0x2bb45a92, 0x5cb36a04,
+    0xc2d7ffa7, 0xb5d0cf31, 0x2cd99e8b, 0x5bdeae1d,
+    0x9b64c2b0, 0xec63f226, 0x756aa39c, 0x026d930a,
+    0x9c0906a9, 0xeb0e363f, 0x72076785, 0x05005713,
+    0x95bf4a82, 0xe2b87a14, 0x7bb12bae, 0x0cb61b38,
+    0x92d28e9b, 0xe5d5be0d, 0x7cdcefb7, 0x0bdbdf21,
+    0x86d3d2d4, 0xf1d4e242, 0x68ddb3f8, 0x1fda836e,
+    0x81be16cd, 0xf6b9265b, 0x6fb077e1, 0x18b74777,
+    0x88085ae6, 0xff0f6a70, 0x66063bca, 0x11010b5c,
+    0x8f659eff, 0xf862ae69, 0x616bffd3, 0x166ccf45,
+    0xa00ae278, 0xd70dd2ee, 0x4e048354, 0x3903b3c2,
+    0xa7672661, 0xd06016f7, 0x4969474d, 0x3e6e77db,
+    0xaed16a4a, 0xd9d65adc, 0x40df0b66, 0x37d83bf0,
+    0xa9bcae53, 0xdebb9ec5, 0x47b2cf7f, 0x30b5ffe9,
+    0xbdbdf21c, 0xcabac28a, 0x53b39330, 0x24b4a3a6,
+    0xbad03605, 0xcdd70693, 0x54de5729, 0x23d967bf,
+    0xb3667a2e, 0xc4614ab8, 0x5d681b02, 0x2a6f2b94,
+    0xb40bbe37, 0xc30c8ea1, 0x5a05df1b, 0x2d02ef8d
+};
+
+quint32 FeatherWeightCachePrivate::crc32(const char *data, uint len)
+{
+    const uchar *p = reinterpret_cast<const uchar *>(data);
+    const uchar *q = p + len;
+    const quint32 init = 0xFFFFFFFFL;
+
+    quint32 crc32 = init;
+    while (p < q) {
+        crc32 = (crc32 >> 8) ^ crc_tbl32[(crc32 ^ *p++) & 0xffL];
+    }
+    return crc32 ^ init ;
+}
+
+void FeatherWeightCachePrivate::storeItem(CacheItem *cacheItem)
+{
+    Q_ASSERT(cacheItem->metaData.saveToDisk());
+
+    QString fileName = cacheFileName(cacheItem->metaData.url());
+    Q_ASSERT(!fileName.isEmpty());
+
+
+    if (currentCacheSize > 0) {
+        currentCacheSize += FILESYSTEMOVERHEAD + cacheItem->size();
+    }
+
+
+    //lut.insert( URL2HASH(cacheItem->metaData.url()), FILESYSTEMOVERHEAD + cacheItem->size() ) ;
+
+    currentCacheSize = (reinterpret_cast<FeatherWeightCache *>(parent()))->expire();
+
+
+
+    if (!cacheItem->file) {
+        QString templateName = tmpCacheFileName();
+        cacheItem->file = new QTemporaryFile(templateName, &cacheItem->data);
+        if (cacheItem->file->open()) {
+            cacheItem->writeHeader(cacheItem->file);
+            cacheItem->writeCompressedData(cacheItem->file);
+        }
+    }
+
+    if (cacheItem->file
+        && cacheItem->file->isOpen()
+        && cacheItem->file->error() == QFile::NoError) {
+        cacheItem->file->setAutoRemove(false);
+        // ### use atomic rename rather then remove & rename
+        if (cacheItem->file->rename(fileName))
+            currentCacheSize += cacheItem->file->size();
+        else {
+            // Presume that the destination file exists and/or is open. So try nuking.
+            bool err1 = QFile::remove(fileName);
+            Q_UNUSED(err1);
+            bool err2 = cacheItem->file->rename(fileName);
+            // You are hopeless. Don't persist
+            if (!err2)  {
+                cacheItem->file->setAutoRemove(true);
+#if defined(FEATHERWEIGHTCACHE_DEBUG)
+                qWarning() << "FeatherWeightCache: couldn't replace the cache file " << fileName;
+#endif
+            }
+        }
+    }
+    if (cacheItem->metaData.url() == lastItem.metaData.url())
+        lastItem.reset();
+}
+
+/*!
+    \reimp
+*/
+bool FeatherWeightCache::remove(const QUrl &url)
+{
+#if defined(FEATHERWEIGHTCACHE_DEBUG)
+    //qDebug() << "FeatherWeightCache::remove()" << url;
+#endif
+
+    // remove is also used to cancel insertions, not a common operation
+    QHashIterator<QIODevice*, CacheItem*> it(d->inserting);
+    while (it.hasNext()) {
+        it.next();
+        CacheItem *item = it.value();
+        if (item && item->metaData.url() == url) {
+            delete item;
+            d->inserting.remove(it.key());
+            return true;
+        }
+    }
+
+    if (d->lastItem.metaData.url() == url)
+        d->lastItem.reset();
+    return d->removeFile(d->cacheFileName(url));
+}
+
+/*!
+    Put all of the misc file removing into one function to be extra safe
+ */
+bool FeatherWeightCachePrivate::removeFile(const QString &file)
+{
+#if defined(FEATHERWEIGHTCACHE_DEBUG)
+    //qDebug() << "FeatherWeightCache::removFile()" << file;
+#endif
+    if (file.isEmpty())
+        return false;
+    QFileInfo info(file);
+    QString fileName = info.fileName();
+    if (!fileName.endsWith(CACHE_POSTFIX))
+        return false;
+    qint64 size = info.size();
+    if (QFile::remove(file)) {
+        currentCacheSize -= size;
+        return true;
+    }
+    return false;
+}
+
+/*!
+    Use signal from worker thread to update disk usage awareness
+ */
+void FeatherWeightCachePrivate::updateCacheSize(qint64 newSize)
+{
+    currentCacheSize = newSize;
+#if defined(FEATHERWEIGHTCACHE_DEBUG)
+    qDebug() << "FeatherWeightCachePrivate::updateCacheSize " << " new size " << currentCacheSize;
+#endif
+}
+
+/*!
+    \reimp
+*/
+QNetworkCacheMetaData FeatherWeightCache::metaData(const QUrl &url)
+{
+#if defined(FEATHERWEIGHTCACHE_DEBUG)
+    //qDebug() << "FeatherWeightCache::metaData()" << url;
+#endif
+    if (d->lastItem.metaData.url() == url)
+        return d->lastItem.metaData;
+    return fileMetaData(d->cacheFileName(url));
+}
+
+/*!
+    Returns the QNetworkCacheMetaData for the cache file \a fileName.
+
+    If \a fileName is not a cache file QNetworkCacheMetaData will be invalid.
+ */
+QNetworkCacheMetaData FeatherWeightCache::fileMetaData(const QString &fileName) const
+{
+#if defined(FEATHERWEIGHTCACHE_DEBUG)
+    //qDebug() << "FeatherWeightCache::fileMetaData()" << fileName;
+#endif
+    QFile file(fileName);
+    if (!file.open(QFile::ReadOnly))
+        return QNetworkCacheMetaData();
+    if (!d->lastItem.read(&file, false)) {
+        file.close();
+        FeatherWeightCachePrivate *that = const_cast<FeatherWeightCachePrivate*>(d);
+        that->removeFile(fileName);
+    }
+    return d->lastItem.metaData;
+}
+
+/*!
+    \reimp
+*/
+QIODevice *FeatherWeightCache::data(const QUrl &url)
+{
+#if defined(FEATHERWEIGHTCACHE_DEBUG)
+    //qDebug() << "FeatherWeightCache::data()" << url;
+#endif
+
+    QScopedPointer<QBuffer> buffer;
+    if (!url.isValid())
+        return 0;
+    if (d->lastItem.metaData.url() == url && d->lastItem.data.isOpen()) {
+        buffer.reset(new QBuffer);
+        buffer->setData(d->lastItem.data.data());
+    } else {
+        QScopedPointer<QFile> file(new QFile(d->cacheFileName(url)));
+        if (!file->open(QFile::ReadOnly | QIODevice::Unbuffered))
+            return 0;
+
+        if (!d->lastItem.read(file.data(), true)) {
+            file->close();
+            remove(url);
+            return 0;
+        }
+        if (d->lastItem.data.isOpen()) {
+            // compressed
+            buffer.reset(new QBuffer);
+            buffer->setData(d->lastItem.data.data());
+        } else {
+            buffer.reset(new QBuffer);
+            // ### verify that QFile uses the fd size and not the file name
+            qint64 size = file->size() - file->pos();
+            const uchar *p = 0;
+#ifndef Q_OS_WINCE
+            p = file->map(file->pos(), size);
+#endif
+            if (p) {
+                buffer->setData((const char *)p, size);
+                file.take()->setParent(buffer.data());
+            } else {
+                buffer->setData(file->readAll());
+            }
+        }
+    }
+    buffer->open(QBuffer::ReadOnly);
+    return buffer.take();
+}
+
+/*!
+    \reimp
+*/
+void FeatherWeightCache::updateMetaData(const QNetworkCacheMetaData &metaData)
+{
+#if defined(FEATHERWEIGHTCACHE_DEBUG)
+    qDebug() << "FeatherWeightCache::updateMetaData()" << metaData.url();
+#endif
+    QUrl url = metaData.url();
+    QIODevice *oldDevice = data(url);
+    if (!oldDevice) {
+#if defined(FEATHERWEIGHTCACHE_DEBUG)
+        qDebug() << "FeatherWeightCache::updateMetaData(), no device!";
+#endif
+        return;
+    }
+
+    QIODevice *newDevice = prepare(metaData);
+    if (!newDevice) {
+#if defined(FEATHERWEIGHTCACHE_DEBUG)
+        qDebug() << "FeatherWeightCache::updateMetaData(), no new device!" << url;
+#endif
+        return;
+    }
+    //TODO: Optimize this somehow?
+    char data[1024];
+    while (!oldDevice->atEnd()) {
+        qint64 s = oldDevice->read(data, 1024);
+        newDevice->write(data, s);
+    }
+    delete oldDevice;
+    insert(newDevice);
+}
+
+/*!
+    Returns the current maximum size for the disk cache.
+
+    \sa setMaximumCacheSize()
+ */
+qint64 FeatherWeightCache::maximumCacheSize() const
+{
+    return d->maximumCacheSize;
+}
+
+/*!
+    Sets the maximum size of the disk cache to be \a size.
+
+    If the new size is smaller then the current cache size then the cache will call expire().
+
+    \sa maximumCacheSize()
+ */
+void FeatherWeightCache::setMaximumCacheSize(qint64 size)
+{
+
+    bool expireCache = (size < d->maximumCacheSize);
+    d->maximumCacheSize = size;
+    if (expireCache)
+        d->currentCacheSize = expire();
+}
+
+/*!
+    Cleans the cache so that its size is under the maximum cache size.
+    Returns the current size of the cache.
+
+    When the current size of the cache is greater than the maximumCacheSize()
+    older cache files are removed until the total size is less then 90% of
+    maximumCacheSize() starting with the oldest ones first using the file
+    creation date to determine how old a cache file is.
+
+    Subclasses can reimplement this function to change the order that cache
+    files are removed taking into account information in the application
+    knows about that FeatherWeightCache does not, for example the number of times
+    a cache is accessed.
+
+    Note: cacheSize() calls expire if the current cache size is unknown.
+
+    \sa maximumCacheSize(), fileMetaData()
+ */
+qint64 FeatherWeightCache::expire()
+{
+
+    if (d->currentCacheSize >= 0 && d->currentCacheSize < maximumCacheSize())
+        return d->currentCacheSize;
+
+    if (cacheDirectory().isEmpty()) {
+        qWarning() << "FeatherWeightCache::expire() The cache directory is not set";
+        return 0;
+    }
+
+#if defined(FEATHERWEIGHTCACHE_DEBUG)
+    qDebug() << "Calling expire, size = " << d->currentCacheSize << " , max = " << maximumCacheSize() ;
+#endif
+    return d->expire();
+}
+
+/*!
+    \reimp
+*/
+void FeatherWeightCache::clear()
+{
+#if defined(FEATHERWEIGHTCACHE_DEBUG)
+    qDebug() << "FeatherWeightCache::clear()";
+#endif
+
+    qint64 size = d->maximumCacheSize;
+    d->maximumCacheSize = 0;
+    d->currentCacheSize = expire();
+    d->maximumCacheSize = size;
+}
+
+qint64 FeatherWeightCachePrivate::expire()
+{
+
+    // ASYNC expiration via background thread
+    beastOfBurden.expireLazily(cacheDirectory, maximumCacheSize);
+
+    // Note: this cache size will not/cannot reflect the reduced
+    // cache size due to the async nature of the expire() above.
+    return currentCacheSize;
+}
+
+QByteArray FeatherWeightCachePrivate::generateId(const QUrl &url)
+{
+    QUrl cleanUrl = url;
+    cleanUrl.setPassword(QString());
+    cleanUrl.setFragment(QString());
+    QByteArray blob = cleanUrl.toEncoded();
+
+    QByteArray hash;
+    hash.setNum(crc32(blob.data(), blob.length()), 16);
+    return hash;
+}
+
+QString FeatherWeightCachePrivate::tmpCacheFileName() const
+{
+    //The subdirectory is presumed to be already read for use.
+    return cacheDirectory + PREPARED_SLASH + QLatin1String("XXXXXX") + CACHE_POSTFIX;
+}
+
+/*!
+    Genrates fully qualified path of cached resource from a URL.
+ */
+QString FeatherWeightCachePrivate::cacheFileName(const QUrl &url) const
+{
+    if (!url.isValid())
+        return QString();
+
+    // map URL to a unique enough signature
+    const QByteArray unique(generateId(url));
+
+    // generates <cache dir>/data/e/cache_beefcafe.cache
+    // where 'e' is the last character of a hex string
+    QString fullpath = cacheDirectory + DATA_SLASH
+                       + QLatin1Char(unique.at(unique.length()-1)) + QLatin1String("/")
+                       + QLatin1String(unique) + CACHE_POSTFIX;
+
+    return  fullpath;
+}
+
+
+/* Important: This c'tor runs in the same thread as main cache */
+WorkerThread::WorkerThread()
+{
+    abort = false;
+}
+
+/* Important: This d'tor runs in the same thread as main cache */
+WorkerThread::~WorkerThread()
+{
+    // The destructor can be called at any point while the thread is active.
+    // So we set abort to true to tell run() to stop running as soon as possible.
+    mutex.lock();
+    abort = true;
+    condition.wakeOne(); // wake up thread if it has nothing to do
+    mutex.unlock();
+
+    wait(); // waits for run() to return
+}
+
+/* Important: This method runs in its own thread, unlike the c'tor and d'tor */
+void WorkerThread::run()
+{
+
+#if defined(Q_OS_SYMBIAN)
+    // Remove this once QTBUG-10271 is fixed
+    RThread myThread;
+    myThread.SetPriority(EPriorityLess);
+#endif
+
+    qint64 size = expireImpl();
+    emit onDiskSizeChanged(size);
+
+#if defined(FEATHERWEIGHTCACHE_DEBUG)
+    qDebug() << "New on-disk cache size: " << size <<  QThread::currentThreadId();
+#endif
+
+
+}
+
+qint64 WorkerThread::expireImpl()
+{
+    QDir::Filters filters = QDir::AllDirs | QDir:: Files | QDir::NoDotAndDotDot;
+    QDirIterator it(this->cacheDir, filters, QDirIterator::Subdirectories);
+
+    QMultiMap<QDateTime, QString> cacheItems;
+    qint64 totalSize = 0;
+    while (it.hasNext()) {
+        QString path = it.next();
+        QFileInfo info = it.fileInfo();
+        QString fileName = info.fileName();
+        if (fileName.endsWith(CACHE_POSTFIX)) {
+            cacheItems.insert(info.created(), path);
+            totalSize += info.size();
+        }
+
+        // Interrupts this slow loop when d'tor is called
+        if (abort) {
+            // potentially incorrect, but can't do any better
+            return totalSize;
+        }
+    }
+
+    int removedFiles = 0;
+    // this goal setting could be made smarter based on max cache size
+    // e.g on desktop with large 50MB caches, freeing 10% is probably enough
+    // but on mobile where caches are smaller (e.g 5MB) and disks are slow, you want
+    // to free atleast 0.5-1MB if going through all this trouble.
+    // Also TODO: Move to LRU algorithm
+    qint64 goal = (this->maxCacheSize * 8) / 10;
+    QMultiMap<QDateTime, QString>::const_iterator i = cacheItems.constBegin();
+    while (i != cacheItems.constEnd()) {
+        if (totalSize < goal)
+            break;
+        QString name = i.value();
+        QFile file(name);
+        qint64 size = file.size();
+        file.remove();
+        totalSize -= size;
+        ++removedFiles;
+        ++i;
+
+        // Interrupts this slow loop when d'tor is called
+        if (abort) {
+            // potentially incorrect, but can't do any better
+            return totalSize;
+        }
+
+    }
+#if defined(FEATHERWEIGHTCACHE_DEBUG)
+    if (removedFiles > 0) {
+        qDebug() << "FeatherWeightCache::expire()"
+                << "Removed:" << removedFiles
+                << "Kept:" << cacheItems.count() - removedFiles;
+    }
+#endif
+
+    //TODO: Why do we do this in the original
+    //implementation? It isn't necessary that
+    //running expiration logics caused last
+    //insertion to become invalid?
+    //if (removedFiles > 0)
+    //    lastItem.reset();
+
+    return totalSize;
+
+}
+
+/* Important: this function runs in the same thread as main cache */
+void WorkerThread::expireLazily(QString cacheDir, qint64 maxCacheSize)
+{
+
+    //lock mutex. unlock automatically when locker goes out of scope
+    QMutexLocker locker(&mutex);
+
+    //make private copy so that other member functions can use this
+    this->cacheDir = cacheDir;
+    this->maxCacheSize = maxCacheSize;
+
+    if (!isRunning()) {
+
+#if defined(FEATHERWEIGHTCACHE_DEBUG)
+        qDebug() << "Starting worker thread a low priority";
+#endif
+
+        start(LowPriority);
+
+    } else {
+
+#if defined(FEATHERWEIGHTCACHE_DEBUG)
+        qDebug() << "Waking up sleeping worker thread";
+#endif
+
+        condition.wakeOne();
+
+    }
+
+}
+
+
+/*!
+    We compress small text and JavaScript files.
+ */
+bool CacheItem::canCompress() const
+{
+#if 1
+    bool sizeOk = false;
+    bool typeOk = false;
+    foreach (QNetworkCacheMetaData::RawHeader header, metaData.rawHeaders()) {
+        if (header.first.toLower() == "content-length") {
+            qint64 size = header.second.toLongLong();
+            if (size > MAX_COMPRESSION_SIZE)
+                return false;
+            else
+                sizeOk = true;
+        }
+
+        if (header.first.toLower() == "content-type") {
+            QByteArray type = header.second;
+            if (type.startsWith("text/")
+                    || (type.startsWith("application/")
+                        && (type.endsWith("javascript") || type.endsWith("ecmascript"))))
+                typeOk = true;
+            else
+                return false;
+        }
+        if (sizeOk && typeOk)
+            return true;
+    }
+    return false;
+#else
+    return false;
+#endif
+
+}
+
+enum
+{
+    CacheMagic = 0xe8,
+    CurrentCacheVersion = 7
+};
+
+void CacheItem::writeHeader(QFile *device) const
+{
+    QDataStream out(device);
+
+    out << qint32(CacheMagic);
+    out << qint32(CurrentCacheVersion);
+    out << metaData;
+    bool compressed = canCompress();
+    out << compressed;
+}
+
+void CacheItem::writeCompressedData(QFile *device) const
+{
+    QDataStream out(device);
+
+    out << qCompress(data.data());
+}
+
+/*!
+    Returns false if the file is a cache file,
+    but is an older version and should be removed otherwise true.
+ */
+bool CacheItem::read(QFile *device, bool readData)
+{
+    reset();
+
+    QDataStream in(device);
+
+    qint32 marker;
+    qint32 v;
+    in >> marker;
+    in >> v;
+    if (marker != CacheMagic)
+        return true;
+
+    // If the cache magic is correct, but the version is not we should remove it
+    if (v != CurrentCacheVersion)
+        return false;
+
+    bool compressed;
+    QByteArray dataBA;
+    in >> metaData;
+    in >> compressed;
+    if (readData && compressed) {
+        in >> dataBA;
+        data.setData(qUncompress(dataBA));
+        data.open(QBuffer::ReadOnly);
+    }
+    return metaData.isValid();
+}
+
+} // namespace WRT
\ No newline at end of file