#include <sys/types.h> #include <sys/socket.h> intsocket(int domain, int type, int 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.
These families are defined in the include file
‹sys/socket.h ›.
The currently understood formats are:
AF_UNIX
UNIX internal protocols
AF_INET
ARPA Internet protocols
AF_INET6
IPv6 (Internet Protocol version 6) protocols
AF_IMPLINK
IMP host at IMP link layer
AF_BLUETOOTH
Bluetooth protocols
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,
and are available only to the superuser.
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 \*(lqcommunication domain\*(rq
in which communication is to take place; see
protocols(5).
A value of 0 for
protocol
will let the system select an appropriate protocol for the requested
socket type.
Sockets of type
SOCK_STREAM
are full-duplex byte streams.
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
ensure 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 an 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
‹sys/socket.h ›.
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.
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.
[EACCES]
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.