4.4BSD/usr/share/man/cat2/socket.0
SOCKET(2) BSD Programmer's Manual SOCKET(2)
NNAAMMEE
ssoocckkeett - create an endpoint for communication
SSYYNNOOPPSSIISS
##iinncclluuddee <<ssyyss//ttyyppeess..hh>>
##iinncclluuddee <<ssyyss//ssoocckkeett..hh>>
_i_n_t
ssoocckkeett(_i_n_t _d_o_m_a_i_n, _i_n_t _t_y_p_e, _i_n_t _p_r_o_t_o_c_o_l);
DDEESSCCRRIIPPTTIIOONN
SSoocckkeett() creates an endpoint for communication and returns a descriptor.
The _d_o_m_a_i_n 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 <_s_y_s_/_s_o_c_k_e_t_._h>.
The currently understood formats are
AF_UNIX (UNIX internal protocols),
AF_INET (ARPA Internet protocols),
AF_ISO (ISO protocols),
AF_NS (Xerox Network Systems protocols), and
AF_IMPLINK (IMP host at IMP link layer).
The socket has the indicated _t_y_p_e, which specifies the semantics of com-
munication. Currently defined types are:
SOCK_STREAM
SOCK_DGRAM
SOCK_RAW
SOCK_SEQPACKET
SOCK_RDM
A SOCK_STREAM type provides sequenced, reliable, two-way connection based
byte streams. An out-of-band data transmission mechanism may be support-
ed. A SOCK_DGRAM socket supports datagrams (connectionless, unreliable
messages of a fixed (typically small) maximum length). A SOCK_SEQPACKET
socket may provide a sequenced, reliable, two-way connection-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 PF_NS.
SOCK_RAW sockets provide access to internal network protocols and inter-
faces. The types SOCK_RAW, which is available only to the super-user,
and SOCK_RDM, which is planned, but not yet implemented, are not de-
scribed here.
The _p_r_o_t_o_c_o_l 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 SOCK_STREAM are full-duplex byte streams, similar to
pipes. A stream socket must be in a _c_o_n_n_e_c_t_e_d 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 re-
ceived 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 will indicate an error with -1 returns and with ETIMEDOUT as the
specific code in the global variable _e_r_r_n_o. The protocols optionally keep
sockets ``warm'' by forcing transmissions roughly every minute in the ab-
sence 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_SEQPACKET sockets employ the same system calls as SOCK_STREAM 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.
SOCK_DGRAM and SOCK_RAW 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 _o_p_t_i_o_n_s. These op-
tions are defined in the file <_s_y_s_/_s_o_c_k_e_t_._h>. Setsockopt(2) and getsock-
opt(2) are used to set and get options, respectively.
RREETTUURRNN VVAALLUUEESS
A -1 is returned if an error occurs, otherwise the return value is a de-
scriptor referencing the socket.
EERRRROORRSS
The ssoocckkeett() 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.
SSEEEE AALLSSOO
accept(2), bind(2), connect(2), getprotoent(3), getsockname(2),
getsockopt(2), ioctl(2), listen(2), read(2), recv(2), select(2),
send(2), shutdown(2), socketpair(2), write(2)
_A_n _I_n_t_r_o_d_u_c_t_o_r_y _4_._3 _B_S_D _I_n_t_e_r_p_r_o_c_e_s_s _C_o_m_m_u_n_i_c_a_t_i_o_n _T_u_t_o_r_i_a_l, reprinted in
UNIX Programmer's Supplementary Documents Volume 1.
_B_S_D _I_n_t_e_r_p_r_o_c_e_s_s _C_o_m_m_u_n_i_c_a_t_i_o_n _T_u_t_o_r_i_a_l, reprinted in UNIX Programmer's
Supplementary Documents Volume 1.
HHIISSTTOORRYY
The ssoocckkeett function call appeared in 4.2BSD.
4.2 Berkeley Distribution June 4, 1993 2