SOCKET(2) SOCKET(2)
NAME
socket - create an endpoint for communication - TCP
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),
PF_NS (Xerox Network Systems protocols), and
PF_IMPLINK (IMP "host at IMP" link layer).
The socket has the indicated type, which specifies the
semantics of communication. 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 supported. 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 interfaces. The types
SOCK_RAW, which is available only to the super-user, and
SOCK_RDM, which is planned, but not yet implemented, are not
described here.
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SOCKET(2) SOCKET(2)
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 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 signal, to exit.
SOCK_SEQPACKET sockets employ the same system calls as
SOCK_STREAM sockets. 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 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.
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
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SOCKET(2) SOCKET(2)
<sys/socket.h>. setsockopt(2) and getsockopt(2) are used to
set and get options, respectively.
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.
SEE ALSO
accept(2), bind(2), connect(2), getsockname(2),
getsockopt(2), ioctl(2), listen(2), read(2), recv(2),
select(2), send(2), socketpair(2), write(2)
ORIGIN
4.3 BSD
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