socket()

Create an endpoint for communication

Synopsis:

#include <sys/types.h>
#include <sys/socket.h>

int socket( int domain, 
            int type, 
            int protocol );

Arguments:

domain

The communications domain that you want to use. This selects the protocol family that should be used. These families are defined in <sys/socket.h>.

type

The type of socket you want to create. This determines the semantics of communication. Here are the currently defined types:

• SOCK_STREAM — provides sequenced, reliable, two-way, connection-based byte streams. An out-of-band data transmission mechanism may be supported.
• SOCK_DGRAM — supports datagrams, which are connectionless, unreliable messages of a fixed (typically small) maximum length.
• SOCK_RAW — provides access to internal network protocols and interfaces. Available only to the superuser, this type isn't described here.

For more information, see below.

protocol

The particular protocol that you want to use with the socket. Normally, only a single protocol exists to support a particular socket type within a given protocol family. But if many protocols exist, you must specify one. The protocol number you give is particular to the communication domain where communication is to take place (see /etc/protocols in the Utilities Reference).

Library:

libsocket

Use the -l socket option to qcc to link against this library.

Description:

The socket() function creates an endpoint for communication and returns a descriptor.

SOCK_STREAM sockets

SOCK_STREAM sockets are full-duplex byte streams, similar to pipes. A stream socket must be in a connected state before any data may be sent or received on it. To create a connection to another socket, call connect() call.

Once the socket is connected, you can transfer data by using read() and write() or some variant of send() and recv(). When a session has been completed, a close() may be performed. Out-of-band data may also be transmitted (as described in send()) and received (as described in recv()).

The communications protocols used to implement a SOCK_STREAM socket ensure that data isn't lost or duplicated. If a piece of data that the peer protocol has buffer space for can't be successfully transmitted within a reasonable length of time, the connection is considered broken and calls will indicate an error by returning -1 and setting errno to ETIMEDOUT.

SOCK_DGRAM and SOCK_RAW sockets

With SOCK_DGRAM and SOCK_RAW sockets, datagrams can be sent to correspondents named in send() calls. Datagrams are generally received with recvfrom(), which returns the next datagram with its return address.

Using the ioctl() call

You can use the ioctl() call to specify a process group to receive a SIGURG signal when the out-of-band data arrives. The call may also enable nonblocking I/O and asynchronous notification of I/O events via SIGIO.

Socket-level options

The operation of sockets is controlled by socket-level options. These options are defined in the file <sys/socket.h>. Use setsockopt() and getsockopt() to set and get options.

Returns:

A descriptor referencing the socket, or -1 if an error occurs (errno is set).

Errors:

EACCES

Permission to create a socket of the specified type and/or protocol is denied.

EAFNOSUPPORT

The specified address family isn't supported.

EMFILE

The per-process descriptor table is full.

ENFILE

The system file table is full.

ENOBUFS

Insufficient buffer space available. The socket can't be created until sufficient resources are freed.

ENOMEM

Not enough memory.

EPROTONOSUPPORT

The protocol type or the specified protocol isn't supported within this domain.

Classification:

POSIX 1003.1

Caveats:

By default, socket() communicates with the TCP/IP stack managing the /dev/socket portion of the namespace. You can change this behavior by setting the SOCK environment variable. For an example, see “Running multiple instances of the TCP/IP stack” in the TCP/IP Networking chapter of the Neutrino User's Guide.

See also:

ICMP6, ICMP, INET6, IPv6, IP, IPsec, ROUTE, TCP, UDP, UNIX protocols

accept(), bind(), close(), connect(), getprotobyname(), getsockname(), getsockopt(), ioctl(), listen(), read(), recv(), select(), send(), shutdown(), socketpair(), write()