Manual Pages for UNIX Darwin command on man socket

SOCKET(2) BSD System Calls Manual SOCKET(2)

NAME

ssoocckkeett - create an endpoint for communication

SYNOPSIS

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

DESCRIPTION

SSoocckkeett() creates an endpoint for communication and returns a descriptor.

The domain parameter specifies a communications domain within which com-

munication will take place; this selects the protocol family which should

be used. These families are defined in the include file .

The currently understood formats are AFUNIX (UNIX internal protocols), AFINET (ARPA Internet protocols), AFISO (ISO protocols), AFNS (Xerox Network Systems protocols), and AFIMPLINK (IMP host at IMP link layer).

The socket has the indicated type, which specifies the semantics of com-

munication. Currently defined types are: SOCKSTREAM SOCKDGRAM SOCKRAW SOCKSEQPACKET SOCKRDM

A SOCKSTREAM type provides sequenced, reliable, two-way connection based

byte streams. An out-of-band data transmission mechanism may be sup-

ported. A SOCKDGRAM socket supports datagrams (connectionless, unreli-

able messages of a fixed (typically small) maximum length). A

SOCKSEQPACKET socket may provide a sequenced, reliable, two-way connec-

tion-based data transmission path for datagrams of fixed maximum length;

a consumer may be required to read an entire packet with each read system call. This facility is protocol specific, and presently implemented only

for PFNS. SOCKRAW sockets provide access to internal network protocols

and interfaces. The types SOCKRAW, which is available only to the

super-user, and SOCKRDM, which is planned, but not yet implemented, are

not described here.

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 speci-

fied in this manner. The protocol number to use is particular to the communication domain in which communication is to take place; see protocols(5).

Sockets of type SOCKSTREAM 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 SOCKSTREAM 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 will 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 sig-

nal, to exit.

SOCKSEQPACKET sockets employ the same system calls as SOCKSTREAM sock-

ets. The only difference is that read(2) calls will return only the amount of data requested, and any remaining in the arriving packet will be discarded.

SOCKDGRAM and SOCKRAW sockets allow sending of datagrams to correspon-

dents 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. It may also enable non-

blocking I/O and asynchronous notification of I/O events via SIGIO.

The operation of sockets is controlled by socket level options. These

options are defined in the file . Setsockopt(2) and

getsockopt(2) are used to set and get options, respectively.

RETURN VALUES

A -1 is returned if an error occurs, otherwise the return value is a

descriptor referencing the socket.

EERRRROORRSS The ssoocckkeett() system call fails if:

[EACCES] Permission to create a socket of the specified type

and/or protocol is denied. [EAFNOSUPPORT] The specified address family is not supported.

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

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

[ENFILE] The system file table is full.

[ENOBUFS] Insufficient buffer space is available. The socket

cannot be created until sufficient resources are freed. [ENOMEM] Insufficient memory was available to fulfill the request. [EPROTONOSUPPORT] The protocol type or the specified protocol is not supported within this domain.

[EPROTOTYPE] The socket type is not supported by the protocol.

If a new protocol family is defined, the socreate process is free to return any desired error code. The ssoocckkeett() system call will pass this error code along (even if it is undefined).

LEGACY SYNOPSIS

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The include file is necessary.

socketpair(2), write(2), getprotoent(3), inet(4), inet6(4), unix(4),

compat(5) An Introductory 4.3 BSD Interprocess Communication Tutorial, reprinted in UNIX Programmer's Supplementary Documents Volume 1. BSD Interprocess Communication Tutorial, reprinted in UNIX Programmer's Supplementary Documents Volume 1. HISTORY The ssoocckkeett() function call appeared in 4.2BSD. 4.2 Berkeley Distribution June 4, 1993 4.2 Berkeley Distribution