HP Rp3440-4 - 9000 - 0 MB RAM Manual

BSD Sockets Interface Programmer’s
Guide
Edition 6
B2355-90136
HP 9000 Networking
E0497
Printed in: United States
© Copyright 1997 Hewlett-Packard Company.

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4

Contents
5
1. BSD Sockets Concepts
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .17
Key Terms and Concepts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .17
How You Can Use BSD Sockets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .20
The Client-Server Model. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .21
Creating a Connection: the Client-Server Model . . . . . . . . . . . . . . . . .21
BSD Sockets Library Routines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .25
2. Using Internet Stream Sockets
Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .29
Preparing Address Variables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .31
Declaring Socket Address Variables . . . . . . . . . . . . . . . . . . . . . . . . . . .31
Getting the Remote Host's Internet Address . . . . . . . . . . . . . . . . . . . .32
Getting the Port Address for the Desired Service . . . . . . . . . . . . . . . .33
Using a Wildcard Local Address . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .34
Writing the Server Process . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .35
Creating a Socket . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .35
Binding a Socket Address to the Server Process's Socket . . . . . . . . . .36
Setting Up the Server to Wait for Connection Requests . . . . . . . . . . .37
Accepting a Connection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .38
Writing the Client Process . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .40
Creating a Socket . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .40
Requesting a Connection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .41
Sending and Receiving Data. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .43
Sending Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .43
Receiving Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .44
Flag Options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .45
Closing a Socket. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .47

6
Contents
Example Using Internet Stream Sockets . . . . . . . . . . . . . . . . . . . . . . . . 48
3. Advanced Topics for Stream Sockets
Socket Options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61
Getting and Setting Socket Options. . . . . . . . . . . . . . . . . . . . . . . . . . . 62
SO_REUSEADDR. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65
SO_KEEPALIVE. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66
SO_DONTROUTE. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67
SO_SNDBUF. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67
SO_RCVBUF. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67
SO_LINGER . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 68
SO_USELOOPBACK . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69
SO_OOBINLINE. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69
SO_SNDLOWAT. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69
SO_RCVLOWAT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70
SO_SNDTIMEO . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70
SO_RCVTIMEO . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70
SO_TYPE. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70
SO_ERROR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70
SO_BROADCAST . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70
SO_REUSEPORT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70
Synchronous I/O Multiplexing with Select. . . . . . . . . . . . . . . . . . . . . . . 72
Sending and Receiving Data Asynchronously . . . . . . . . . . . . . . . . . . . . 75
Nonblocking I/O . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77
Using Shutdown. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 78
When to Shut Down a Socket. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79
Using Read and Write to Make Stream Sockets Transparent . . . . . . . 80
Sending and Receiving Out-of-band Data. . . . . . . . . . . . . . . . . . . . . . . . 81

Contents
7
4. Using Internet Datagram Sockets
Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .86
Preparing Address Variables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .88
Declaring Socket Address Variables . . . . . . . . . . . . . . . . . . . . . . . . . . .88
Getting the Remote Host's Network Address. . . . . . . . . . . . . . . . . . . .89
Getting the Port Address for the Desired Service . . . . . . . . . . . . . . . .90
Using a Wildcard Local Address . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .91
Writing the Server and Client Processes . . . . . . . . . . . . . . . . . . . . . . . . .92
Creating Sockets. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .92
Binding Socket Addresses to Datagram Sockets . . . . . . . . . . . . . . . . .93
Sending and Receiving Messages . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .95
Sending Messages . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .95
Receiving Messages . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .96
Flag Options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .98
Closing a Socket. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .100
Example Using Datagram Sockets. . . . . . . . . . . . . . . . . . . . . . . . . . . . .101
5. Advanced Topics for Internet Datagram Sockets
SO_BROADCAST Socket Option . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .111
Specifying a Default Socket Address . . . . . . . . . . . . . . . . . . . . . . . . . . .112
When to Specify a Default Socket Address. . . . . . . . . . . . . . . . . . . . .113
Synchronous I/O Multiplexing with Select. . . . . . . . . . . . . . . . . . . . . . .114
Sending and Receiving Data Asynchronously . . . . . . . . . . . . . . . . . . . .115
Sending and Receiving IP Multicast Datagrams. . . . . . . . . . . . . . . . . .116
Sending IP Multicast Datagrams . . . . . . . . . . . . . . . . . . . . . . . . . . . .116
Receiving IP Multicast Datagrams . . . . . . . . . . . . . . . . . . . . . . . . . . .118
Nonblocking I/O. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .121

8
Contents
Using Broadcast Addresses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 122
6. Using UNIX Domain Stream Sockets
Overview. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 124
Preparing Address Variables. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 126
Declaring Socket Address Variables . . . . . . . . . . . . . . . . . . . . . . . . . 126
Writing the Server Process . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 128
Creating a Socket . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 128
Binding a Socket Address to the Server Process's Socket . . . . . . . . 129
Setting the Server Up to Wait for Connection Requests. . . . . . . . . . 130
Accepting a Connection. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 131
Writing the Client Process. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 133
Creating a Socket . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 133
Requesting a Connection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 134
Sending and Receiving Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 136
Sending Data. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 136
Receiving Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 137
Flag Options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 138
Closing a Socket . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 139
Example Using UNIX Domain Stream Sockets . . . . . . . . . . . . . . . . . . 140
7. Using UNIX Domain Datagram Sockets
Overview. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 148
Preparing Address Variables. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 150
Declaring Socket Address Variables . . . . . . . . . . . . . . . . . . . . . . . . . 150
Writing the Server and Client Processes . . . . . . . . . . . . . . . . . . . . . . . 152
Creating Sockets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 152
Binding Socket Addresses to UNIX Domain Datagram Sockets . . . 153

Contents
9
Sending and Receiving Messages . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .155
Sending Messages . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .155
Receiving Messages . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .156
Closing a Socket. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .159
Example Using UNIX Domain Datagram Sockets . . . . . . . . . . . . . . . .160
8. Programming Hints
Troubleshooting. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .167
Using Diagnostic Utilities as Troubleshooting Tools. . . . . . . . . . . . . . .168
Adding a Server Process to the Internet Daemon . . . . . . . . . . . . . . . . .169
Summary Tables for System and Library Calls. . . . . . . . . . . . . . . . . . .173
Portability Issues. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .177
Porting Issues for IPC Functions and Library Calls . . . . . . . . . . . . .177
Porting Issues for Other Functions and Library Calls Typically Used by
IPC178
A. BSD Sockets Quick Reference Table
Quick Reference Table. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .182
Glossary

10
Contents

11
Printing History
The manual printing date and part number indicate its current edition.
The printing date will change when a new edition is printed. Minor
changes may be made at reprint without changing the printing date. the
manual part number will change when extensive changes are made.
Manual updates may be issued between editions to correct errors or
document product changes. To ensure that you receive the updated or
new editions, you should subscribe to the appropriate product support
service. See your HP sales representative for details.
First Edition: February 1991
Second Edition: July 1992 (HP-UX Release 9.0)
Third Edition: January 1995 (HP-UX Release 10.0)
Fourth Edition: December 1995 (HP-UX Release 10.10)
Fifth Edition: June 1996
Sixth Edition: April 1997 (HP-UX Release 10.30)

12

13
Preface
This guide describes HP's BSD Sockets. BSD Sockets is a set of
programming development tools for interprocess communication. HP's
implementation of BSD Sockets is a full set of sockets from the
networking services originally developed by the University of California
at Berkeley (UCB).
The BSD Sockets Interface Programmer's Guide is the primary reference
for programmers who write or maintain BSD Sockets applications on HP
9000 computers. This guide also provides information about BSD Sockets
features for node managers who design HP 9000 networks.
This guide is written for intermediate to advanced programmers and
assumes that:
• Your HP 9000 networking is installed and running on your local host.
• You have all the login names you may be associated with (these may
be obtained from your node manager).
• You have a list of other hosts or nodes your HP 9000 product can
communicate with (this list may also be obtained from your node
manager).
This guide is organized as follows:
Chapter 1 BSD Sockets Concepts provides an overview of the
Client-Server Model.
Chapter 2 Using Internet Stream Sockets describes the steps
involved in creating an internet stream socket using
the AF_INET address family.
Chapter 3 Advanced Topics for Stream Sockets explains
socket options, synchronous I/O multiplexing with
select, sending and receiving data asynchronously,
nonblocking I/O, using shutdown, using read and
write to make stream sockets transparent, and
sending and receiving out-of- band data.
Chapter 4 Using Internet Datagram Sockets describes the
steps involved in creating an internet datagram socket
connection.

14
Chapter 5 Advanced Topics for Internet Datagram Sockets
includes information about default socket address,
synchronous I/O multiplexing with select, sending
and receiving IP multicast datagrams, and broadcast
addresses.
Chapter 6 Using UNIX Domain Stream Sockets describes the
steps involved in creating a UNIX Domain stream
socket connection between two processes executing on
the same node.
Chapter 7 Using UNIX Domain Datagram Sockets describes
the steps required to exchange data between AF_UNIX
datagram sockets on the same node without
establishing a connection.
Chapter 8 Programming Hints contains information about
troubleshooting, port addresses, diagnostic utilities,
internet daemon, inetd, portability issues, and system
and library calls.
Appendix A BSD Sockets Quick Reference Table summarizes
the differences in calls for the two sets of sockets
behavior: HP-UX BSD Sockets and X/Open Sockets.

15
1 BSD Sockets Concepts
The BSD Sockets facility allows you to create distributed applications
that pass data between programs (on the same computer or on separate
computers on the network) without requiring an understanding of the

16 Chapter1
BSD Sockets Concepts
many layers of networking protocols. This is accomplished by using a set
of system calls. These system calls allow you to create communication
endpoints called sockets and transfer data between them.
NOTE BSD Sockets is a program development tool. Before you attempt to use
BSD Sockets, you may need to familiarize yourself with the C
programming language and the HP-UX operating system. You could
implement a BSD Sockets application using FORTRAN or Pascal, but all
library calls and include files are implemented in C.

Chapter 1 17
BSD Sockets Concepts
Introduction
Introduction
This guide describes the steps involved in establishing and using BSD
Sockets connections. It also describes the protocols you must use and
how the BSD Sockets system calls interact. The details of each system
call are described in the corresponding man pages.
Key Terms and Concepts
For a basic understanding of BSD Sockets and its general model, you
should review the following terms and definitions.
address family The address format used to interpret addresses
specified in socket operations. The internet address
family (AF_INET) and the Berkeley UNIX Domain
address family (AF_UNIX) are supported.
addressing A means of labeling a socket so that it is
distinguishable from other sockets on a host.
association A BSD Sockets connection is defined by an
association. An AF_INET association contains the
(protocol, local address, local port, remote address,
remote port)-tuple. An AF_UNIX association
contains the (protocol, local address, peer
address)-tuple. Associations must be unique;
duplicate associations on the same host cannot
exist. The tuple is created when the local and
remote socket addresses are bound and connected.
This means that the association is created in two
steps, and there is a chance that two potential
associations could be alike between steps. The host
prevents duplicate associations by checking for
uniqueness of the tuple at connection time, and
reporting an error if the tuple is not unique.

18 Chapter1
BSD Sockets Concepts
Introduction
binding Before a socket can be accessed across the network,
it must be bound to an address. Binding associates a
socket address with a socket and makes the socket
accessible to other sockets on the network. Once a
socket address is bound, other sockets can connect
to the socket and send data to or receive data from
it.
channel Communication path created by establishing a
connection between sockets.
communication
domain A set of properties that describes the characteristics of processes communicating through sockets. The
internet (AF_INET) address family domain is
supported. The UNIX Domain (AF_UNIX) address
family domain is also supported, for local
communication only.
internet
address A four-byte address that identifies a node on the network.
message The data sent in one UDP packet.
packet A message or data unit that is transmitted between
communicating processes.
peer The remote process with which a process
communicates.
port An address within a host that is used to
differentiate between multiple sockets with the
same internet address. You can use port address
values 1024 through 65535. (Port addresses 1
through 1023 are reserved for the super-user.)
protocols Two internet transport layer protocols can be used
with BSD Sockets. They are TCP, which implements
stream sockets, and UDP, which implements
datagram sockets.
socket Sockets are communication endpoints. A pair of
connected sockets provides an interface similar to
that of HP-UX pipes. A socket is identified by a
socket descriptor.

Chapter 1 19
BSD Sockets Concepts
Introduction
socket address For the internet address family (AF_INET), the
socket address consists of the internet address, port
address and address family of a socket. The internet
and port address combination allows the network to
locate a socket. For UNIX Domain (AF_UNIX), the
socket address is the directory pathname bound to
the socket.
socket
descriptor A socket descriptor is an HP-UX file descriptor that references a socket instead of an ordinary file.
Therefore, it can be used for reading, writing, or
most standard file system calls after a BSD Sockets
connection is established. System calls that use file
descriptors (e.g. read,write,select) can be used
with socket descriptors. All BSD Sockets functions
use socket descriptors as arguments.
TCP Provides the underlying communication support for
stream sockets. The Transmission Control Protocol
(TCP) is used to implement reliable, sequenced,
flow-controlled two-way communication based on
byte streams similar to pipes. Refer to the tcp(7p)
man page for more information on TCP.
UDP Provides the underlying communication support for
datagram sockets. The User Datagram Protocol
(UDP) is an unreliable protocol. A process receiving
messages on a datagram socket could find messages
are duplicated, out-of-sequence, or missing.
Messages retain their record boundaries and are
sent as individually addressed packets. There is no
concept of a connection between the communicating
sockets. Refer to the udp(7p) man page for more
information on UDP.
UNIX Domain
Protocol In addition, the UNIX Domain protocol may be used with AF_UNIX sockets for interprocess
communication on the same node. Refer to the
unix(7p) man page for more information on the
UNIX Domain protocol.

20 Chapter1
BSD Sockets Concepts
How You Can Use BSD Sockets
How You Can Use BSD Sockets
The best example of how BSD Sockets can be used is the Internet
Services. These services use BSD Sockets to communicate between
remote hosts. Using the BSD Sockets facility, you can write your own
distributed application programs to do a variety of tasks.
For example, you can write distributed application programs to:
• Access a remote database.
• Access multiple computers at one time.
• Spread tasks across several hosts.