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.
For example if I have this code:
QString str;
stream >> str;
It will fail silently if no data is currently there in the socket. Is there a way to tell it to block instead?
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;
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;
};
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;
};