QUdpSocket bind problem

[JonB]

This post is deleted!

[jsulm]

@JulsPower You are blocking the Qt event loop with such a loop, not sure that is the issue here

[Hanson]

@JulsPower Hi
Maybe you can check what the error value for m_UdpSocket->state() means first.
https://doc.qt.io/qt-6/qabstractsocket.html#SocketState-enum

[JulsPower]

Ok I changed the init function to be more like it should be

    ui->setupUi(this);
    m_UdpSocket = new QUdpSocket(this);
    bool b;
    b = m_UdpSocket->bind(QHostAddress::Any, 55555);
    auto state = m_UdpSocket->state();
    QMessageBox::information(this, "info", QString(b?"true ":"false ") + QString::number(state));
    connect(m_UdpSocket, &QUdpSocket::readyRead, this, &MainWindow::readPendingDatagrams);
    connect(m_UdpSocket, &QUdpSocket::errorOccurred, this, &MainWindow::errorOccurred);

if I debug the message box show false 0 (which is unconnected)
and if I run the debug version it shows true 4

errorOccurred is never called

[Hanson]

@JulsPower
You can now use error() or errorString() to see the actual error message.
https://doc.qt.io/qt-6/qabstractsocket.html#error
https://doc.qt.io/qt-6/qiodevice.html#errorString

[JulsPower]

indeed
QMessageBox::information(this, "info", QString(b?"true ":"false ") + QString::number(state) + m_UdpSocket->errorString());
return unknow error :(

[Hanson]

@JulsPower What is return value of error().

[JulsPower]

@Hanson said in QUdpSocket bind problem:

@JulsPower What is return value of error().

-1

[Hanson]

@JulsPower
I checked the relevant source code and I can see that the error code without an error message could be WSANOTINITIALISED, which stands for WSAStartup failed. I guess it could be a mismatch or missing winsock library in the debug environment.
https://learn.microsoft.com/zh-cn/windows/win32/winsock/windows-sockets-error-codes-2

bool QNativeSocketEnginePrivate::nativeBind(const QHostAddress &a, quint16 port)
{
    QHostAddress address = a;
    if (address.protocol() == QAbstractSocket::IPv4Protocol) {
        if ((address.toIPv4Address() & 0xffff0000) == 0xefff0000) {
            // binding to a multicast address
            address = QHostAddress(QHostAddress::AnyIPv4);
        }
    }

    qt_sockaddr aa;
    QT_SOCKLEN_T sockAddrSize = 0;
    setPortAndAddress(port, address, &aa, &sockAddrSize);

    if (aa.a.sa_family == AF_INET6) {
        // The default may change in future, so set it explicitly
        int ipv6only = 0;
        if (address.protocol() == QAbstractSocket::IPv6Protocol)
            ipv6only = 1;
        ::setsockopt(socketDescriptor, IPPROTO_IPV6, IPV6_V6ONLY, (char*)&ipv6only, sizeof(ipv6only) );
    }


    int bindResult = ::bind(socketDescriptor, &aa.a, sockAddrSize);
    if (bindResult == SOCKET_ERROR && WSAGetLastError() == WSAEAFNOSUPPORT
            && address.protocol() == QAbstractSocket::AnyIPProtocol) {
        // retry with v4
        aa.a4.sin_family = AF_INET;
        aa.a4.sin_port = htons(port);
        aa.a4.sin_addr.s_addr = htonl(address.toIPv4Address());
        sockAddrSize = sizeof(aa.a4);
        bindResult = ::bind(socketDescriptor, &aa.a, sockAddrSize);
    }
    if (bindResult == SOCKET_ERROR) {
        int err = WSAGetLastError();
        WS_ERROR_DEBUG(err);
        switch (err) {
        case WSANOTINITIALISED:
            //###
            break;
        case WSAEADDRINUSE:
        case WSAEINVAL:
            setError(QAbstractSocket::AddressInUseError, AddressInuseErrorString);
            break;
        case WSAEACCES:
            setError(QAbstractSocket::SocketAccessError, AddressProtectedErrorString);
            break;
        case WSAEADDRNOTAVAIL:
            setError(QAbstractSocket::SocketAddressNotAvailableError, AddressNotAvailableErrorString);
            break;
        default:
            break;
        }

#if defined (QNATIVESOCKETENGINE_DEBUG)
        qDebug("QNativeSocketEnginePrivate::nativeBind(%s, %i) == false (%s)",
               address.toString().toLatin1().constData(), port, socketErrorString.toLatin1().constData());
#endif

        return false;
    }

#if defined (QNATIVESOCKETENGINE_DEBUG)
    qDebug("QNativeSocketEnginePrivate::nativeBind(%s, %i) == true",
           address.toString().toLatin1().constData(), port);
#endif
    socketState = QAbstractSocket::BoundState;
    return true;
}

[JulsPower]

Interesting
would you know a way to confirm this? and even more fix it?

[JulsPower]

I did update to qt creator 17 with all debug symbol, issue remain

[Hanson]

@JulsPower
You can try the following code before executing the bind() function

#include <winsock2.h>
#include <ws2tcpip.h>
#pragma comment(lib, "ws2_32.lib")

....
WSAData wsadata;
int err = WSAStartup(MAKEWORD(2,0), &wsadata);
if (err != 0) {
        qWarning("QTcpSocketAPI: WinSock v2.0 initialization failed.");
    } 
....

[JulsPower]

@Hanson said in QUdpSocket bind problem:

@JulsPower
You can try the following code before executing the bind() function

#include <winsock2.h>
#include <ws2tcpip.h>
#pragma comment(lib, "ws2_32.lib")

....
WSAData wsadata;
int err = WSAStartup(MAKEWORD(2,0), &wsadata);
if (err != 0) {
        qWarning("QTcpSocketAPI: WinSock v2.0 initialization failed.");
    } 
....

WSAStartup return 0 so no error there
but the bind function continue to return false

[Hanson]

@JulsPower
emmm... I can't figure it out anymore :)
Or you can download the qt source code and debug it.

[JulsPower]

WSAGetLastError return error 10106 (WSAEPROVIDERFAILEDINIT)
gives you an idea??

[Hanson]

@JulsPower
Can you show me where in your code calling WSAGetLastError()?

[JulsPower]

@Hanson said in QUdpSocket bind problem:

@JulsPower
Can you show me where in your code calling WSAGetLastError()?

b = m_UdpSocket->bind(QHostAddress::Any, 55555);
auto state = m_UdpSocket->state();
QMessageBox::information(this, "info", QString(b?"true ":"false ") + QString::number(state) + QString::number(WSAGetLastError()));

show while debugging it shows false 010106

[JulsPower]

I replicated the samething in a new project using qmake instead of cmake. lo and behold it works in debugging mode...
seem ill be using qmake

[Hanson]

@JulsPower
Maybe same as this question
https://stackoverflow.com/questions/48597996/qtcpserver-return-unknown-error-on-listen-function-only-under-debugger
https://developercommunity.visualstudio.com/t/native-cmake-support-application-debug-launch-is-b/562174

So the reason could be that when debugging the program with cmake project, the environment variables were cleared and the SystemRoot variable was missing, which caused WSASocket to fail to load the related components.

[Hanson]

This post is deleted!