使用 QDataStream 从 QTcpSocket 读取

问题描述

我需要通过 QTcpSocket 发送二进制数据.我正在考虑使用 QDataStream，但我遇到了一个问题 - 如果在我尝试读取时没有数据到达，它会默默地失败.

I need to send binary data through a QTcpSocket. I was thinking about using QDataStream, but I've encountered a problem - it silently fails if no data has arrived at the time I try to read.

例如，如果我有这个代码:

For example if I have this code:

QString str;
stream >> str;

如果套接字中当前没有数据，它将静默失败.有没有办法让它改为阻止?

It will fail silently if no data is currently there in the socket. Is there a way to tell it to block instead?

推荐答案

我根据@Marek 的想法重新编写了代码并创建了 2 个类 - BlockReader 和 BlockWriter:

I reworked the code from @Marek's idea and created 2 classes - BlockReader and BlockWriter:

// Write block to the socket.
BlockWriter(socket).stream() << QDir("C:/Windows").entryList() << QString("Hello World!");

....

// Now read the block from the socket.
QStringList infoList;
QString s;
BlockReader(socket).stream() >> infoList >> s;
qDebug() << infoList << s;

BlockReader:

class BlockReader
{
public:
    BlockReader(QIODevice *io)
    {
        buffer.open(QIODevice::ReadWrite);
        _stream.setVersion(QDataStream::Qt_4_8);
        _stream.setDevice(&buffer);

        quint64 blockSize;

        // Read the size.
        readMax(io, sizeof(blockSize));
        buffer.seek(0);
        _stream >> blockSize;

        // Read the rest of the data.
        readMax(io, blockSize);
        buffer.seek(sizeof(blockSize));
    }

    QDataStream& stream()
    {
        return _stream;
    }

private:
    // Blocking reads data from socket until buffer size becomes exactly n. No
    // additional data is read from the socket.
    void readMax(QIODevice *io, int n)
    {
        while (buffer.size() < n) {
            if (!io->bytesAvailable()) {
                io->waitForReadyRead(30000);
            }
            buffer.write(io->read(n - buffer.size()));
        }
    }
    QBuffer buffer;
    QDataStream _stream;
};

块写入器:

class BlockWriter
{
public:
    BlockWriter(QIODevice *io)
    {
        buffer.open(QIODevice::WriteOnly);
        this->io = io;
        _stream.setVersion(QDataStream::Qt_4_8);
        _stream.setDevice(&buffer);

        // Placeholder for the size. We will get the value
        // at the end.
        _stream << quint64(0);
    }

    ~BlockWriter()
    {
        // Write the real size.
        _stream.device()->seek(0);
        _stream << (quint64) buffer.size();

        // Flush to the device.
        io->write(buffer.buffer());
    }

    QDataStream &stream()
    {
        return _stream;
    }

private:
    QBuffer buffer;
    QDataStream _stream;
    QIODevice *io;
};

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