UDP fragmentation and reassembly

[Guni]

Hi, I'm using SFML 2.0 release candidate, but I am learning how to use the Network package with the SFML 1.6 tutorial for now.

In this tutorial: http://www.sfml-dev.org/tutorials/1.6/network-packets.php

The third problem is more network related. Data transfers through TCP and UDP protocols must follow some rules defined by the lower levels of implementation. In particular, a chunk of data can be split and received in several parts ; the receiver must then find a way to recompose the chunk and return data as if it was received in once.

This seems to imply that SFML will handle fragmentation and reassembly of packets if you send too large packets. If you send a large packet with UDP, and it is split up into a number of smaller packets, if even one of those packets fails to send, will the entire message be lost?

[Laurent]

This is no longer true in SFML 2.0. UDP datagrams are not split.

[Guni]

Well, I believe UDP fragments packets at the IP level, and that if even one of those packets is lost, the whole packet is lost. So I'm guessing if you send a large UDP packet using sf::UdpSocket::send(), it will be fragmented at the IP level. But SFML will not know about this fragmentation, and so it cannot do anything about this fragmentation. sf::UdpSocket is just a somewhat thin layer over using UDP sockets directly. Is this correct or not?

[Laurent]

Totally correct

sf::UdpSocket doesn't add any robustness on top of the UDP protocol.