socket(3N) LIBRARY FUNCTIONS socket(3N)
NAME
socket - create an endpoint for communication
SYNOPSIS
#include <sys/types.h>
#include <sys/socket.h>
int socket(domain, type, protocol)
int 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 pro-
tocol 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
/usr/include/sys/socket.h. There must be an entry in the
netconfig(4) file for at least each protocol family and type
required. If protocol has been specified, but no exact match
for the tuplet family, type, protocol is found, then the
first entry containing the specified family and type with
zero for protocol will be used. The currently understood
formats are:
PFUNIX UNIX system internal protocols
PFINET ARPA Internet protocols The socket has
the indicated type, which specifies the
communication semantics. 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 transmis-
sion mechanism may be supported. A
SOCKDGRAM socket supports datagrams
(connectionless, unreliable messages of
a fixed (typically small) maximum
length). A SOCKSEQPACKET 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 not implemented
for any protocol family. SOCKRAW
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socket(3N) LIBRARY FUNCTIONS socket(3N)
sockets provide access to internal net-
work interfaces. The types SOCKRAW,
which is available only to the super-
user, and SOCKRDM, for which no imple-
mentation currently exists, are not
described here. 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, multiple protocols may exist,
in which case a particular protocol must
be specified in this manner. The proto-
col number to use is particular to the
"communication domain" in which communi-
cation is to take place. If a protocol
is specified by the caller, then it will
be packaged into a socket level option
request and sent to the underlying pro-
tocol layers. 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(3N) call.
Once connected, data may be transferred
using read(2) and write(2) calls or some
variant of the send(3N) and recv(3N)
calls. When a session has been com-
pleted, a close(2) may be performed.
Out-of-band data may also be transmitted
as described on the send(3N) manual page
and received as described on the
recv(3N) manual page. The communica-
tions 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 indi-
cated if no response can be elicited on
an otherwise idle connection for a
extended period (for instance 5
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socket(3N) LIBRARY FUNCTIONS socket(3N)
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.
SOCKSEQPACKET sockets employ the same
system calls as SOCKSTREAM sockets.
The only difference is that read calls
will return only the amount of data
requested, and any remaining in the
arriving packet will be discarded.
SOCKDGRAM and SOCKRAW sockets allow
datagrams to be sent to correspondents
named in sendto calls. Datagrams are
generally received with recvfrom, 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 with SIGIO
signals. The operation of sockets is
controlled by socket level options.
These options are defined in the file
/usr/include/sys/socket.h.
setsockopt(3N) and getsockopt(3N) are
used to set and get options, respec-
tively.
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 pro-
tocol is not supported within this
domain.
EMFILE The per-process descriptor table is
full.
EACCESS Permission to create a socket of the
specified type and/or protocol is
denied.
ENOMEM Insufficient user memory is available.
ENOSR There were insufficient STREAMS
resources available to complete the
operation.
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socket(3N) LIBRARY FUNCTIONS socket(3N)
SEE ALSO
close(2), fcntl(2), ioctl(2), read(2), write(2), accept(3N),
bind(3N), connect(3N), getsockname(3N), getsockopt(3N),
listen(3N), recv(3N), send(3N), shutdown(3N),
socketpair(3N).
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