Sockets: Internet Domains 1235the one specified in port. (This may not return the desired result in the few cases
mentioned above where the same port number maps to different service names in
UDP and TCP.)An example of the use of the getservbyname() function is provided in the file
files/t_getservbyname.c in the source code distribution for this book.59.14 UNIX Versus Internet Domain Sockets
When writing applications that communicate over a network, we must necessarily
use Internet domain sockets. However, when using sockets to communicate
between applications on the same system, we have the choice of using either Inter-
net or UNIX domain sockets. In the case, which domain should we use and why?
Writing an application using just Internet domain sockets is often the simplest
approach, since it will work on both a single host and across a network. However,
there are some reasons why we may choose to use UNIX domain sockets:z On some implementations, UNIX domain sockets are faster than Internet
domain sockets.
z We can use directory (and, on Linux, file) permissions to control access to
UNIX domain sockets, so that only applications with a specified user or group
ID can connect to a listening stream socket or send a datagram to a datagram
socket. This provides a simple method of authenticating clients. With Internet
domain sockets, we need to do rather more work if we wish to authenticate clients.
z Using UNIX domain sockets, we can pass open file descriptors and sender creden-
tials, as summarized in Section 61.13.3.59.15 Further Information
There is a wealth of printed and online resources on TCP/IP and the sockets API:z The key book on network programming with the sockets API is [Stevens at al.,
2004]. [Snader, 2000] adds some useful guidelines on sockets programming.
z [Stevens, 1994] and [Wright & Stevens, 1995] describe TCP/IP in detail.
[Comer, 2000], [Comer & Stevens, 1999], [Comer & Stevens, 2000], [Kozierok,
2005], and [Goralksi, 2009] also provide good coverage of the same material.
z [Tanenbaum, 2002] provides general background on computer networks.
z [Herbert, 2004] describes the details of the Linux 2.6 TCP/IP stack.
z The GNU C library manual (online at http://www.gnu.org/) has an extensive dis-
cussion of the sockets API.
z The IBM Redbook, TCP/IP Tutorial and Technical Overview, provides lengthy
coverage of networking concepts, TCP/IP internals, the sockets API, and a host
of related topics. It is freely downloadable from http://www.redbooks.ibm.com/.
z [Gont, 2008] and [Gont, 2009b] provide security assessments of IPv4 and TCP.
z The Usenet newsgroup comp.protocols.tcp-ip is dedicated to questions related to
the TCP/IP networking protocols.