QNetworkSession Class

Member Function Documentation

QNetworkSession::QNetworkSession(const QNetworkConfiguration &connectionConfig, QObject *parent = nullptr)

Constructs a session based on connectionConfig with the given parent.

See also QNetworkConfiguration.

[virtual] QNetworkSession::~QNetworkSession()

Frees the resources associated with the QNetworkSession object.

[slot] void QNetworkSession::accept()

Instructs the session to permanently accept the new access point. Once this function has been called the session may not return to the old access point.

The old access point may be closed in the process if there are no other network sessions for it. Therefore any open socket that still uses the old access point may become unusable and should be closed before completing the migration.

quint64 QNetworkSession::activeTime() const

Returns the number of seconds that the session has been active.

quint64 QNetworkSession::bytesReceived() const

Returns the amount of data received in bytes; otherwise 0.

This field value includes the usage across all open network sessions which use the same network interface.

If the session is based on a service network configuration the number of sent bytes across all active member configurations are returned.

This function may not always be supported on all platforms and returns 0. The platform capability can be detected via QNetworkConfigurationManager::DataStatistics.

Note: On some platforms this function may run the main event loop.

quint64 QNetworkSession::bytesWritten() const

Returns the amount of data sent in bytes; otherwise 0.

This field value includes the usage across all open network sessions which use the same network interface.

If the session is based on a service network configuration the number of sent bytes across all active member configurations are returned.

This function may not always be supported on all platforms and returns 0. The platform capability can be detected via QNetworkConfigurationManager::DataStatistics.

Note: On some platforms this function may run the main event loop.

[slot] void QNetworkSession::close()

Decreases the session counter on the associated network configuration. If the session counter reaches zero the active network interface is shut down. This also means that state() will only change from Connected to Disconnected if the current session was the last open session.

If the platform does not support out-of-process sessions calling this function does not stop the interface. In this case stop() has to be used to force a shut down. The platform capabilities can be detected via QNetworkConfigurationManager::capabilities().

Note that this call is asynchronous. Depending on the outcome of this call the results can be enquired by connecting to the stateChanged(), opened() or error() signals.

See also open(), stop(), and isOpen().

[signal] void QNetworkSession::closed()

This signal is emitted when the network session has been closed.

QNetworkConfiguration QNetworkSession::configuration() const

Returns the QNetworkConfiguration that this network session object is based on.

See also QNetworkConfiguration.

QNetworkSession::SessionError QNetworkSession::error() const

Returns the type of error that last occurred.

See also state() and errorString().

[signal] void QNetworkSession::error(QNetworkSession::SessionError error)

This signal is emitted after an error occurred. The error parameter describes the error that occurred.

Note: Signal error is overloaded in this class. To connect to this signal by using the function pointer syntax, Qt provides a convenient helper for obtaining the function pointer as shown in this example:

connect(networkSession, QOverload<QNetworkSession::SessionError>::of(&QNetworkSession::error),
    [=](QNetworkSession::SessionError error){ /* ... */ });

See also error() and errorString().

QString QNetworkSession::errorString() const

Returns a human-readable description of the last device error that occurred.

See also error().

[slot] void QNetworkSession::ignore()

This function indicates that the application does not wish to roam the session.

See also migrate().

QNetworkInterface QNetworkSession::interface() const

Returns the network interface that is used by this session.

This function only returns a valid QNetworkInterface when this session is Connected.

The returned interface may change as a result of a roaming process.

See also state().

bool QNetworkSession::isOpen() const

Returns true if this session is open. If the number of all open sessions is greater than zero the underlying network interface will remain connected/up.

The session can be controlled via open() and close().

[slot] void QNetworkSession::migrate()

Instructs the session to roam to the new access point. The old access point remains active until the application calls accept().

The newConfigurationActivated() signal is emitted once roaming has been completed.

See also accept().

[signal] void QNetworkSession::newConfigurationActivated()

This signal is emitted once the session has roamed to the new access point. The application may reopen its socket and test the suitability of the new network link. Subsequently it must either accept() or reject() the new access point.

See also accept() and reject().

[slot] void QNetworkSession::open()

Creates an open session which increases the session counter on the underlying network interface. The system will not terminate a network interface until the session reference counter reaches zero. Therefore an open session allows an application to register its use of the interface.

As a result of calling open() the interface will be started if it is not connected/up yet. Some platforms may not provide support for out-of-process sessions. On such platforms the session counter ignores any sessions held by another process. The platform capabilities can be detected via QNetworkConfigurationManager::capabilities().

Note that this call is asynchronous. Depending on the outcome of this call the results can be enquired by connecting to the stateChanged(), opened() or error() signals.

It is not a requirement to open a session in order to monitor the underlying network interface.

See also close(), stop(), and isOpen().

[signal] void QNetworkSession::opened()

This signal is emitted when the network session has been opened.

The underlying network interface will not be shut down as long as the session remains open. Note that this feature is dependent on system wide session support.

[signal] void QNetworkSession::preferredConfigurationChanged(const QNetworkConfiguration &config, bool isSeamless)

This signal is emitted when the preferred configuration/access point for the session changes. Only sessions which are based on service network configurations may emit this signal. config can be used to determine access point specific details such as proxy settings and isSeamless indicates whether roaming will break the sessions IP address.

As a consequence to this signal the application must either start the roaming process by calling migrate() or choose to ignore() the new access point.

If the roaming process is non-seamless the IP address will change which means that a socket becomes invalid. However seamless mobility can ensure that the local IP address does not change. This is achieved by using a virtual IP address which is bound to the actual link address. During the roaming process the virtual address is attached to the new link address.

Some platforms may support the concept of Forced Roaming and Application Level Roaming (ALR). Forced roaming implies that the platform may simply roam to a new configuration without consulting applications. It is up to the application to detect the link layer loss and reestablish its sockets. In contrast ALR provides the opportunity to prevent the system from roaming. If this session is based on a configuration that supports roaming the application can choose whether it wants to be consulted (ALR use case) by connecting to this signal. For as long as this signal connection remains the session remains registered as a roaming stakeholder; otherwise roaming will be enforced by the platform.

See also migrate(), ignore(), and QNetworkConfiguration::isRoamingAvailable().

[slot] void QNetworkSession::reject()

The new access point is not suitable for the application. By calling this function the session returns to the previous access point/configuration. This action may invalidate any socket that has been created via the not desired access point.

See also accept().

QVariant QNetworkSession::sessionProperty(const QString &key) const

Returns the value for property key.

A network session can have properties attached which may describe the session in more details. This function can be used to gain access to those properties.

The following property keys are guaranteed to be specified on all platforms:

QNetworkConfigurationManager mgr;
QNetworkConfiguration ap = mgr.defaultConfiguration();
QNetworkSession *session = new QNetworkSession(ap);
... //code activates session

QString ident = session->sessionProperty("ActiveConfiguration").toString();
if ( ap.type() == QNetworkConfiguration::ServiceNetwork ) {
    Q_ASSERT( ap.identifier() != ident );
    Q_ASSERT( ap.children().contains( mgr.configurationFromIdentifier(ident) ) );
} else if ( ap.type() == QNetworkConfiguration::InternetAccessPoint ) {
    Q_ASSERT( ap.identifier() == ident );
}

See also setSessionProperty().

void QNetworkSession::setSessionProperty(const QString &key, const QVariant &value)

Sets the property value on the session. The property is identified using key. Removing an already set property can be achieved by passing an invalid QVariant.

Note that the UserChoiceConfiguration and ActiveConfiguration properties are read only and cannot be changed using this method.

See also sessionProperty().

QNetworkSession::State QNetworkSession::state() const

Returns the state of the session.

If the session is based on a single access point configuration the state of the session is the same as the state of the associated network interface. Therefore a network session object can be used to monitor network interfaces.

A QNetworkConfiguration::ServiceNetwork based session summarizes the state of all its children and therefore returns the Connected state if at least one of the service network's children() configurations is active.

Note that it is not required to hold an open session in order to obtain the network interface state. A connected but closed session may be used to monitor network interfaces whereas an open and connected session object may prevent the network interface from being shut down.

See also error() and stateChanged().

[signal] void QNetworkSession::stateChanged(QNetworkSession::State state)

This signal is emitted whenever the state of the network session changes. The state parameter is the new state.

See also state().

[slot] void QNetworkSession::stop()

Invalidates all open sessions against the network interface and therefore stops the underlying network interface. This function always changes the session's state() flag to Disconnected.

See also open() and close().

QNetworkSession::UsagePolicies QNetworkSession::usagePolicies() const

Returns the network usage policies currently in force by the system.

[signal] void QNetworkSession::usagePoliciesChanged(QNetworkSession::UsagePolicies usagePolicies)

This signal is emitted when the usagePolicies in force are changed by the system.

This function was introduced in Qt 5.0.

bool QNetworkSession::waitForOpened(int msecs = 30000)

Waits until the session has been opened, up to msecs milliseconds. If the session has been opened, this function returns true; otherwise it returns false. In the case where it returns false, you can call error() to determine the cause of the error.

The following example waits up to one second for the session to be opened:

session->open();
if (session->waitForOpened(1000))
    qDebug("Open!");

If msecs is -1, this function will not time out.

See also open() and error().