SOCKET(2) — Kubota Pacfic Computer Inc. (System Calls−BSD)

NAME

socket − create an endpoint for communication

SYNOPSIS

#include <sys/types.h>
#include <sys/socket.h>
s = socket(domain, type, protocol)
int s, domain, type, protocol;

DESCRIPTION

socket creates an endpoint for communication and returns a descriptor.

The domain parameter specifies a communications domain within which communication will take place; this selects the protocol family which should be used. The protocol family generally is the same as the address family for the addresses supplied in later operations on the socket. These families are defined in the include file <sys/socket.h>. The currently understood formats are

PF_UNIX(UNIX internal protocols),
PF_INET(ARPA Internet protocols),

The socket has the indicated type, which specifies the semantics of communication. Currently defined types are:

SOCK_STREAM
SOCK_DGRAM
SOCK_RAW

A SOCK_STREAM type provides sequenced, reliable, two-way connection based byte streams. An out-of-band data transmission mechanism may be supported. A SOCK_DGRAM socket supports datagrams (connectionless, unreliable messages of a fixed (typically small) maximum length). SOCK_RAW sockets provide access to internal network protocols and interfaces. The type SOCK_RAW is available only to the super-user.

The protocol specifies a particular protocol to be used with the socket. Normally only a single protocol exists to support a particular socket type within a given protocol family. However, it is possible that many protocols may exist, in which case a particular protocol must be specified in this manner. The protocol number to use is particular to the “communication domain” in which communication is to take place; see protocols(3N).

Sockets of type SOCK_STREAM 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. A connection to another socket is created with a connect(2) call. Once connected, data may be transferred using read(2) and write(2) calls or some variant of the send(2) and recv(2) calls. When a session has been completed a close(2) may be performed. Out-of-band data may also be transmitted as described in send(2) and received as described in recv(2).

The communications protocols used to implement a SOCK_STREAM insure that data is not lost or duplicated. If a piece of data for which the peer protocol has buffer space cannot be successfully transmitted within a reasonable length of time, then the connection is considered broken and calls indicate an error with −1 returns and with ETIMEDOUT as the specific code in the global variable errno. The protocols optionally keep sockets “warm” by forcing transmissions roughly every minute in the absence of other activity. An error is then indicated if no response can be elicited on an otherwise idle connection for a extended period (e.g. 5 minutes). A SIGPIPE signal is raised if a process sends on a broken stream; this causes naive processes, which do not handle the signal, to exit.

SOCK_DGRAM and SOCK_RAW sockets allow sending of datagrams to correspondents named in send(2) calls. Datagrams are generally received with recvfrom(2), which returns the next datagram with its return address.

An fcntl(2) call can be used to specify a process group to receive a SIGURG signal when the out-of-band data arrives.

RETURN VALUE

A −1 is returned if an error occurs, otherwise the return value is a descriptor referencing the socket.

ERRORS

The socket call fails if:

[EPROTONOSUPPORT]
The protocol type or the specified protocol is not supported within this domain.

[EMFILE] The per-process descriptor table is full.

[ENFILE] The system file table is full.

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

[ENOBUFS] Insufficient buffer space is available. The socket cannot be created until sufficient resources are freed.

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