class QNetworkDatagram

The QNetworkDatagram class provides the data and metadata of a UDP datagram. More…

Synopsis

Methods

Note

This documentation may contain snippets that were automatically translated from C++ to Python. We always welcome contributions to the snippet translation. If you see an issue with the translation, you can also let us know by creating a ticket on https:/bugreports.qt.io/projects/PYSIDE

Detailed Description

QNetworkDatagram can be used with the QUdpSocket class to represent the full information contained in a UDP (User Datagram Protocol) datagram. QNetworkDatagram encapsulates the following information of a datagram:

  • the payload data;

  • the sender address and port number;

  • the destination address and port number;

  • the remaining hop count limit (on IPv4, this field is usually called “time to live” - TTL);

  • the network interface index the datagram was received on or to be sent on.

QUdpSocket will try to match a common behavior as much as possible on all operating systems, but not all of the metadata above can be obtained in some operating systems. Metadata that cannot be set on the datagram when sending with writeDatagram() will be silently discarded.

Upon reception, the senderAddress() and senderPort() properties contain the address and port of the peer that sent the datagram, while destinationAddress() and destinationPort() contain the target that was contained in the datagram. That is usually an address local to the current machine, but it can also be an IPv4 broadcast address (such as “255.255.255.255”) or an IPv4 or IPv6 multicast address. Applications may find it useful to determine if the datagram was sent specifically to this machine via unicast addressing or whether it was sent to multiple destinations.

When sending, the senderAddress() and senderPort() should contain the local address to be used when sending. The sender address must be an address that is assigned to this machine, which can be obtained using QNetworkInterface , and the port number must be the port number that the socket is bound to. Either field can be left unset and will be filled in by the operating system with default values. The destinationAddress() and destinationPort() fields may be set to a target address different from the one the UDP socket is currently associated with.

Usually, when sending a datagram in reply to a datagram previously received, one will set the destinationAddress() to be the senderAddress() of the incoming datagram and similarly for the port numbers. To facilitate this common process, QNetworkDatagram provides the function makeReply() .

The hopCount() function contains, for a received datagram, the remaining hop count limit for the packet. When sending, it contains the hop count limit to be set. Most protocols will leave this value set to the default and let the operating system decide on the best value to be used. Multicasting over IPv4 often uses this field to indicate the scope of the multicast group (link-local, local to an organization or global).

The interfaceIndex() function contains the index of the operating system’s interface that received the packet. This value is the same one that can be set on a scopeId() property and matches the index() property. When sending packets to global addresses, it is not necessary to set the interface index as the operating system will choose the correct one using the system routing table. This property is important when sending datagrams to link-local destinations, whether unicast or multicast.

Feature support

Some features of QNetworkDatagram are not supported in all operating systems. Only the address and ports of the remote host (sender in received packets and destination for outgoing packets) are supported in all systems. On most operating systems, the other features are supported only for IPv6. Software should check at runtime whether the rest could be determined for IPv4 addresses.

The current feature support is as follows:

Operating system

Local address

Hop count

Interface index

FreeBSD

Supported

Supported

Only for IPv6

Linux

Supported

Supported

Supported

OS X

Supported

Supported

Only for IPv6

Other Unix supporting RFC 3542

Only for IPv6

Only for IPv6

Only for IPv6

Windows (desktop)

Supported

Supported

Supported

Windows RT

Not supported

Not supported

Not supported

See also

QUdpSocket QNetworkInterface

__init__()

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, writeDatagram() will attempt to send the datagram to the address last associated with, by using connectToHost() .

__init__(other)
Parameters:

other – QNetworkDatagram

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

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

__init__(data[, destinationAddress=QHostAddress()[, port=0]])
Parameters:

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

clear()

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

data()
Return type:

QByteArray

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()

destinationAddress()
Return type:

QHostAddress

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 isNull() .

destinationPort()
Return type:

int

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.

hopLimit()
Return type:

int

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()

interfaceIndex()
Return type:

int

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 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.

isNull()
Return type:

bool

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

isValid()
Return type:

bool

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.

makeReply(payload)
Parameters:

payload – QByteArray

Return type:

QNetworkDatagram

senderAddress()
Return type:

QHostAddress

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 isNull() .

senderPort()
Return type:

int

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.

setData(data)
Parameters:

data – QByteArray

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()

setDestination(address, port)
Parameters:

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.

setHopLimit(count)
Parameters:

count – int

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()

setInterfaceIndex(index)
Parameters:

index – int

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 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 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.

setSender(address[, port=0])
Parameters:

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.

swap(other)
Parameters:

other – QNetworkDatagram

Swaps this instance with other.