自定义 QAbstractNetworkCache 实现;QAbstractNetworkCache::insert(Q

custom QAbstractNetworkCache implementation; QAbstractNetworkCache::insert(QIODevice *device) device has no data

本文关键字：QAbstractNetworkCache insert 实现 自定义      更新时间：2023-10-16

我正在尝试构建自己的自定义QAbstractNetworkCache实现以用于QNetworkAccessManager。

我在QAbstractNetworkCache::insert(QIODevice *device)时遇到问题;在此方法中，设备始终以 0 字节读取

。

据我了解，从QAbstractNetworkCache::prepare(const QNetworkCacheMetaData &metaData)返回的QIODevice*将填充数据，并在QNetworkAccessManager完成下载后用作QAbstractNetworkCache::insert(QIODevice *device)方法的参数。

所以我准备了一个QBuffer来成为这个容器，但是每当QAbstractNetworkCache::insert(QIODevice *device)被调用时，它总是带着任何东西到达(device->bytesAvailable() == 0) 

QIODevice* NetworkCachePrivate::prepare(const QNetworkCacheMetaData &metaData) {
        if (!metaData.isValid() || !metaData.url().isValid() || cacheDir.isEmpty()) return 0;
        QIODevice* device = 0;
        QString hash = hexMD5(metaData.url().toString());
        QScopedPointer<QBuffer> buffer(new QBuffer);
        if (buffer->open(QIODevice::ReadWrite))
        {
                qDebug() << "BUFFER READY";
                device = buffer.take();
                deviceMapping[device] = qMakePair(hash, metaData);
        }
        return device;
}
void NetworkCachePrivate::insert(QIODevice *device) {
        if (deviceMapping.contains(device))
        {
                QPair<QString, QNetworkCacheMetaData> pair = deviceMapping[device];
                QString fileName;
                fileName += cacheDir;
                fileName += QLatin1String("/");
                fileName += pair.first;
                qDebug() << "DEVICE BYTES" << device->bytesAvailable(); //ALWAYS 0!!!! :(
                QFile file(fileName);
                if (file.open(QIODevice::WriteOnly))
                {
                        qint64 size = file.write(device->readAll());
                        if (size <= 0)
                        {
                                file.remove();
                        }
                        else
                        {
                                qDebug() << "FILE WROTE " << size;
                                cacheSize += size;
                        }
                }
                deviceMapping.remove(device);
                delete device;
        }
}
QNetworkCacheMetaData NetworkCachePrivate::metaData (const QUrl &url ) {
    QString fileName;
    fileName += cacheDir; 
    fileName += QLatin1String("/"); 
    fileName += hexMD5(url.toString());
    QNetworkCacheMetaData data;
    if (!QFile::exists(fileName))
        return data;
    data.setUrl(url); 
    data.setExpirationDate(QDateTime::currentDateTime().addYears(1));
    return data;
}

正如 peppe 在评论中还指出的那样，您需要根据文档在写入后和读取之前寻找开头的QBuffer：

QBuffer 允许您使用 QIODevice 接口访问 QByteArray。QByteArray 被视为标准的随机访问文件。例：

QBuffer buffer;
char ch;
buffer.open(QBuffer::ReadWrite);
buffer.write("Qt rocks!");
*** buffer.seek(0); ***
buffer.getChar(&ch);  // ch == 'Q'
buffer.getChar(&ch);  // ch == 't'
buffer.getChar(&ch);  // ch == ' '
buffer.getChar(&ch);  // ch == 'r'

为了使您的代码更具体，您需要插入如下语句：

...
device.seek(0);
qDebug() << "DEVICE BYTES" << device->bytesAvailable(); //NOT 0 ANYMORE!!!! :)
...
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