How do I know that the client has connected to the server?
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This is working fine for me:
#include <QtNetwork> int main(int argc, char* argv[]) { QCoreApplication app(argc, argv); QTcpServer server; if (!server.listen(QHostAddress::Any, 50153)) return 1; QObject::connect(&server, &QTcpServer::newConnection, &server, [&server]() { QTcpSocket *socket = server.nextPendingConnection(); qDebug() << "client connected from" << socket->peerAddress() << ":" << socket->peerPort(); socket->write("Test\n"); socket->flush(); socket->waitForBytesWritten(300); socket->close(); }); QTcpSocket client; QObject::connect(&client, &QTcpSocket::readyRead, &client, [&client]() { qDebug() << client.readAll(); QCoreApplication::quit(); }); client.connectToHost("localhost", 50153); return app.exec(); }@Christian-Ehrlicher said in How do I know that the client has connected to the server?:
socket->flush(); socket->waitForBytesWritten(300);Does one have to have these two lines prior to
socket->close(), or are you just being "safe"? -
The waitForBytesWritten() is needed.
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@NintyS said in How do I know that the client has connected to the server?:
No, I'm not sure but when I close the program then I have a message "connected", so I thinking I connect with my server.
Sorry but please be more precise. Why do you get a 'connected' when you close a program? This doesn't sounds very useful. What program is this? Please use a simple QTcpSocket as shown in the QTcpServer examples to check your program. Or try to connect with e.g. telnet to your listen port.
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@Christian-Ehrlicher I know now why. I use a printf() to show the result. Now when I use qDebug I see my result after connection.
@NintyS
printf()is liable to be at least line-buffered, maybe even fully buffered. You would have to follow it withfflush(stdout)to try to see the output immediately.fprintf(stderr, ...)would probably be better. In any caseqDebug()is a better choice for debugging. -
The waitForBytesWritten() is needed.
@Christian-Ehrlicher said in How do I know that the client has connected to the server?:
the waitForBytesWritten() is needed.
Why? My understanding was that
waitForBytesWritten()is only required if not event queue is available... But without event queue, theconnect()won't work.It is an old maxim of mine that when you have excluded the impossible, whatever remains, however improbable, must be the truth. (Sherlock Holmes)
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@Christian-Ehrlicher said in How do I know that the client has connected to the server?:
the waitForBytesWritten() is needed.
Why? My understanding was that
waitForBytesWritten()is only required if not event queue is available... But without event queue, theconnect()won't work.@KroMignon Because of the close() directly afterwards. I'm pretty sure close() will call flush() before but it's not documented.
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@Christian-Ehrlicher said in How do I know that the client has connected to the server?:
the waitForBytesWritten() is needed.
Why? My understanding was that
waitForBytesWritten()is only required if not event queue is available... But without event queue, theconnect()won't work.@KroMignon probably because of the immediate call to close on the socket
you could alternatively, potentially nest lambdas
QTcpSocket *socket = server.nextPendingConnection(); qDebug() << "client connected from" << socket->peerAddress() << ":" << socket->peerPort(); QByteArray data{"Test\n"}; QObject::connect(socket, &QTcpSocket::bytesWritten, socket, [socket, bytesToSend = data.size()](qint64 bytes)->void{ static qint64 bytesSend{0}; bytesSend += bytes; if(static_cast<qint64>(bytesToSend) == bytesSend) socket->close(); }); socket->write(data); });
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@KroMignon probably because of the immediate call to close on the socket
you could alternatively, potentially nest lambdas
QTcpSocket *socket = server.nextPendingConnection(); qDebug() << "client connected from" << socket->peerAddress() << ":" << socket->peerPort(); QByteArray data{"Test\n"}; QObject::connect(socket, &QTcpSocket::bytesWritten, socket, [socket, bytesToSend = data.size()](qint64 bytes)->void{ static qint64 bytesSend{0}; bytesSend += bytes; if(static_cast<qint64>(bytesToSend) == bytesSend) socket->close(); }); socket->write(data); });@J-Hilk said in How do I know that the client has connected to the server?:
you could alternatively, potentially nest lambdas
QTcpSocket *socket = server.nextPendingConnection(); qDebug() << "client connected from" << socket->peerAddress() << ":" << socket->peerPort(); QByteArray data{"Test\n"}; QObject::connect(socket, &QTcpSocket::bytesWritten, socket, [socket, bytesToSend = data.size()](qint64 bytes)->void{ static qint64 bytesSend{0}; bytesSend += bytes; if(static_cast<qint64>(bytesToSend) == bytesSend) socket->close(); }); socket->write(data); });Hmm, I would do it like this:
QTcpSocket *socket = server.nextPendingConnection(); qDebug() << "client connected from" << socket->peerAddress() << ":" << socket->peerPort(); QByteArray data{"Test\n"}; QObject::connect(socket, &QTcpSocket::bytesWritten, socket, [socket](qint64 bytes)->void{ if(socket->bytesToWrite() == 0) socket->close(); }); socket->write(data);It is an old maxim of mine that when you have excluded the impossible, whatever remains, however improbable, must be the truth. (Sherlock Holmes)
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@J-Hilk said in How do I know that the client has connected to the server?:
you could alternatively, potentially nest lambdas
QTcpSocket *socket = server.nextPendingConnection(); qDebug() << "client connected from" << socket->peerAddress() << ":" << socket->peerPort(); QByteArray data{"Test\n"}; QObject::connect(socket, &QTcpSocket::bytesWritten, socket, [socket, bytesToSend = data.size()](qint64 bytes)->void{ static qint64 bytesSend{0}; bytesSend += bytes; if(static_cast<qint64>(bytesToSend) == bytesSend) socket->close(); }); socket->write(data); });Hmm, I would do it like this:
QTcpSocket *socket = server.nextPendingConnection(); qDebug() << "client connected from" << socket->peerAddress() << ":" << socket->peerPort(); QByteArray data{"Test\n"}; QObject::connect(socket, &QTcpSocket::bytesWritten, socket, [socket](qint64 bytes)->void{ if(socket->bytesToWrite() == 0) socket->close(); }); socket->write(data);@KroMignon potentially, I'm not familiar enough with the inner workings of QAbstractSocket to say for sure, that bytesToWrite is updated before bytesWritten is emitted 🤷♂️
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@KroMignon probably because of the immediate call to close on the socket
you could alternatively, potentially nest lambdas
QTcpSocket *socket = server.nextPendingConnection(); qDebug() << "client connected from" << socket->peerAddress() << ":" << socket->peerPort(); QByteArray data{"Test\n"}; QObject::connect(socket, &QTcpSocket::bytesWritten, socket, [socket, bytesToSend = data.size()](qint64 bytes)->void{ static qint64 bytesSend{0}; bytesSend += bytes; if(static_cast<qint64>(bytesToSend) == bytesSend) socket->close(); }); socket->write(data); });@J-Hilk said in How do I know that the client has connected to the server?:
static qint64 bytesSend{0};You might like to come join us in my question about this over at https://forum.qt.io/topic/123582/static-in-lambda ? :)
