QNetworkDatagram Class

Member Function Documentation

Creates a new QNetworkDatagram representing a reply to this incoming datagram and sets the payload data to payload. This function is a very convenient way of responding to a datagram back to the original sender.

Example:

void Server::readPendingDatagrams()
{
    while (udpSocket->hasPendingDatagrams()) {
        QNetworkDatagram datagram = udpSocket->receiveDatagram();
        QByteArray replyData = processThePayload(datagram.data());
        udpSocket->writeDatagram(datagram.makeReply(replyData));
    }
}

This function is especially convenient since it will automatically copy parameters from this datagram to the new datagram as appropriate:

• this datagram's sender address and port are copied to the new datagram's destination address and port;
• this datagram's interface index, if any, is copied to the new datagram's interface index;
• this datagram's destination address and port are copied to the new datagram's sender address and port only if the address is IPv6 global (non-multicast) address;
• the hop count limit on the new datagram is reset to the default (-1);

If QNetworkDatagram is modified in a future version of Qt to carry further metadata, this function will copy that metadata as appropriate.

This datagram's destination address is not copied if it is an IPv4 address because it is not possible to tell an IPv4 broadcast address apart from a regular IPv4 address without an exhaustive search of all addresses assigned to this machine. Attempting to send a datagram with the sender address equal to the broadcast address is likely to fail. However, this should not affect the communication as network interfaces with multiple IPv4 addresses are uncommon, so the address the operating system will select will likely be one the peer will understand.

Note: This function comes with both rvalue- and lvalue-reference qualifier overloads, so it is a good idea to make sure this object is rvalue, if possible, before calling makeReply, so as to make better use of move semantics. To achieve that, the example above would use:

udpSocket->writeDatagram(std::move(datagram).makeReply(replyData));

QNetworkDatagram::QNetworkDatagram()

Creates a QNetworkDatagram object with no payload data and undefined destination address.

The payload can be modified by using setData() and the destination address can be set with setDestination().

If the destination address is left undefined, QUdpSocket::writeDatagram() will attempt to send the datagram to the address last associated with, by using QUdpSocket::connectToHost().

QNetworkDatagram::QNetworkDatagram(const QByteArray &data, const QHostAddress &destinationAddress = QHostAddress(), quint16 port = 0)

Creates a QNetworkDatagram object and sets data as the payload data, along with destinationAddress and port as the destination address of the datagram.

QNetworkDatagram::QNetworkDatagram(const QNetworkDatagram &other)

Creates a copy of the other datagram, including the payload and metadata.

To create a datagram suitable for sending in a reply, use QNetworkDatagram::makeReply();

QNetworkDatagram::QNetworkDatagram(QNetworkDatagram &&other)

Move-copy constructor.

QNetworkDatagram::~QNetworkDatagram()

Destroys the instance of QNetworkDatagram.

void QNetworkDatagram::clear()

Clears the payload data and metadata in this QNetworkDatagram object, resetting them to their default values.

QByteArray QNetworkDatagram::data() const

Returns the data payload of this datagram. For a datagram received from the network, it contains the payload of the datagram. For an outgoing datagram, it is the datagram to be sent.

Note that datagrams can be transmitted with no data, so the returned QByteArray may be empty.

See also setData().

QHostAddress QNetworkDatagram::destinationAddress() const

Returns the destination address associated with this datagram. For a datagram received from the network, it is the address the peer node sent the datagram to, which can either be a local address of this machine or a multicast or broadcast address. For an outgoing datagrams, it is the address the datagram should be sent to.

If no destination address was set on this datagram, the returned object will report true to QHostAddress::isNull().

See also senderAddress(), destinationPort(), and setDestination().

int QNetworkDatagram::destinationPort() const

Returns the port number of the destination associated with this datagram. For a datagram received from the network, it is the local port number that the peer node sent the datagram to. For an outgoing datagram, it is the peer port the datagram should be sent to.

If no destination address was associated with this datagram, this function returns -1.

See also destinationAddress(), senderPort(), and setDestination().

int QNetworkDatagram::hopLimit() const

Returns the hop count limit associated with this datagram. The hop count limit is the number of nodes that are allowed to forward the IP packet before it expires and an error is sent back to the sender of the datagram. In IPv4, this value is usually known as "time to live" (TTL).

If this datagram was received from the network, this is the remaining hop count of the datagram after reception and was decremented by 1 by each node that forwarded the packet. A value of -1 indicates that the hop limit count not be obtained.

If this is an outgoing datagram, this is the value to be set in the IP header upon sending. A value of -1 indicates the operating system should choose the value.

See also setHopLimit().

uint QNetworkDatagram::interfaceIndex() const

Returns the interface index this datagram is associated with. The interface index is a positive number that uniquely identifies the network interface in the operating system. This number matches the value returned by QNetworkInterface::index() for the interface.

If this datagram was received from the network, this is the index of the interface that the packet was received from. If this is an outgoing datagram, this is the index of the interface that the datagram should be sent on.

A value of 0 indicates that the interface index is unknown.

See also setInterfaceIndex().

bool QNetworkDatagram::isNull() const

Returns true if this QNetworkDatagram object is null. This function is the opposite of isValid().

bool QNetworkDatagram::isValid() const

Returns true if this QNetworkDatagram object is valid. A valid QNetworkDatagram object contains at least one sender or receiver address. Valid datagrams can contain empty payloads.

QHostAddress QNetworkDatagram::senderAddress() const

Returns the sender address associated with this datagram. For a datagram received from the network, it is the address of the peer node that sent the datagram. For an outgoing datagrams, it is the local address to be used when sending.

If no sender address was set on this datagram, the returned object will report true to QHostAddress::isNull().

See also destinationAddress(), senderPort(), and setSender().

int QNetworkDatagram::senderPort() const

Returns the port number of the sender associated with this datagram. For a datagram received from the network, it is the port number that the peer node sent the datagram from. For an outgoing datagram, it is the local port the datagram should be sent from.

If no sender address was associated with this datagram, this function returns -1.

See also senderAddress(), destinationPort(), and setSender().

void QNetworkDatagram::setData(const QByteArray &data)

Sets the data payload of this datagram to data. It is usually not necessary to call this function on received datagrams. For outgoing datagrams, this function sets the data to be sent on the network.

Since datagrams can empty, an empty QByteArray is a valid value for data.

See also data().

void QNetworkDatagram::setDestination(const QHostAddress &address, quint16 port)

Sets the destination address associated with this datagram to be the address address and port number port. The destination address and port numbers are usually set by QUdpSocket upon reception, so there's no need to call this function on a received datagram.

For outgoing datagrams, this function can be used to set the address the datagram should be sent to. It can be the unicast address used to communicate with the peer or a broadcast or multicast address to send to a group of devices.

See also QUdpSocket::writeDatagram(), destinationAddress(), destinationPort(), and setSender().

void QNetworkDatagram::setHopLimit(int count)

Sets the hop count limit associated with this datagram to count. The hop count limit is the number of nodes that are allowed to forward the IP packet before it expires and an error is sent back to the sender of the datagram. In IPv4, this value is usually known as "time to live" (TTL).

It is usually not necessary to call this function on datagrams received from the network.

If this is an outgoing packet, this is the value to be set in the IP header upon sending. The valid range for the value is 1 to 255. This function also accepts a value of -1 to indicate that the operating system should choose the value.

See also hopLimit().

void QNetworkDatagram::setInterfaceIndex(uint index)

Sets the interface index this datagram is associated with to index. The interface index is a positive number that uniquely identifies the network interface in the operating system. This number matches the value returned by QNetworkInterface::index() for the interface.

It is usually not necessary to call this function on datagrams received from the network.

If this is an outgoing packet, this is the index of the interface the datagram should be sent on. A value of 0 indicates that the operating system should choose the interface based on other factors.

Note that the interface index can also be set with QHostAddress::setScopeId() for IPv6 destination addresses and then with setDestination(). If the scope ID set in the destination address and index are different and neither is zero, it is undefined which interface the operating system will send the datagram on.

See also interfaceIndex() and setInterfaceIndex().

void QNetworkDatagram::setSender(const QHostAddress &address, quint16 port = 0)

Sets the sender address associated with this datagram to be the address address and port number port. The sender address and port numbers are usually set by QUdpSocket upon reception, so there's no need to call this function on a received datagram.

For outgoing datagrams, this function can be used to set the address the datagram should carry. The address address must usually be one of the local addresses assigned to this machine, which can be obtained using QNetworkInterface. If left unset, the operating system will choose the most appropriate address to use given the destination in question.

The port number port must be the port number associated with the socket, if there is one. The value of 0 can be used to indicate that the operating system should choose the port number.

See also QUdpSocket::writeDatagram(), senderAddress(), senderPort(), and setDestination().

void QNetworkDatagram::swap(QNetworkDatagram &other)

Swaps this instance with other.

QNetworkDatagram &QNetworkDatagram::operator=(const QNetworkDatagram &other)

Copies the other datagram, including the payload and metadata.

To create a datagram suitable for sending in a reply, use QNetworkDatagram::makeReply();

QNetworkDatagram &QNetworkDatagram::operator=(QNetworkDatagram &&other)

Move-assignment operator.