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NAME
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       socket - create an endpoint for communication
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SYNOPSIS
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       #include <network.h>
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       int socket(int domain, int type, int protocol);
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DESCRIPTION
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       Socket creates an endpoint for communication and returns a
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       descriptor.
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       The domain parameter  specifies  a  communications  domain
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       within  which  communication will take place; this selects
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       the protocol family which should be used.  These  families
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       are  defined  in <sys/socket.h>.  The currently understood
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       formats include:
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       PF_INET
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              IPv4 Internet protocols; see ip(4)
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       The socket has the indicated  type,  which  specifies  the
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       semantics of communication.  Currently defined types are:
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       SOCK_STREAM
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              Provides  sequenced,  reliable, two-way connection-
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              based byte streams.  An out-of-band data  transmis-
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              sion mechanism may be supported.
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       SOCK_DGRAM
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              Supports datagrams (connectionless, unreliable mes-
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              sages of a fixed maximum length).
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       SOCK_SEQPACKET
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              Provides a sequenced, reliable, two-way connection-
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              based data transmission path for datagrams of fixed
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              maximum length; a consumer is required to  read  an
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              entire packet with each read system call.
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       SOCK_RAW
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              Provides raw network protocol access.
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       The  protocol  specifies  a particular protocol to be used
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       with the socket.  Normally only a single  protocol  exists
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       to  support a particular socket type within a given proto-
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       col family.  However, it is possible that  many  protocols
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       may  exist,  in  which  case a particular protocol must be
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       specified in this manner.  The protocol number to  use  is
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       particular to the "communication domain" in which communi-
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       cation is to take place; see  protocols(5).   See  getpro-
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       toent(3)  on  how to map protocol name strings to protocol
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       numbers.
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       Sockets of type SOCK_STREAM are full-duplex byte  streams,
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       similar  to pipes.  A stream socket must be in a connected
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       state before any data may be sent or received  on  it.   A
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       connection  to another socket is created with a connect(2)
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       call.  Once  connected,  data  may  be  transferred  using
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       read(2)  and write(2) calls or some variant of the send(2)
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       and recv(2) calls.  When a session has  been  completed  a
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       close(2)  may  be performed.  Out-of-band data may also be
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       transmitted  as  described  in  send(2)  and  received  as
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       described in recv(2).
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       The communications protocols which implement a SOCK_STREAM
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       ensure that data is not lost or duplicated.  If a piece of
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       data  for  which the peer protocol has buffer space cannot
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       be successfully transmitted within a reasonable length  of
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       time,  then the connection is considered When SO_KEEPALIVE
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       is enabled on the socket the protocol checks in  a  proto-
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       col-specific  manner  if  the other end is still alive.
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       SOCK_DGRAM and SOCK_RAW sockets allow sending of datagrams
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       to correspondents named in send(2) calls.   Datagrams  are
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       generally  received  with  recvfrom(2),  which returns the
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       next datagram with its return address.
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       When  the network signals an error condition to the proto-
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       col module (e.g.  using a ICMP message for IP) the pending
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       error  flag  is set for the socket.  The next operation on
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       this socket will return the  error  code  of  the  pending
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       error.  For some protocols it is possible to enable a per-
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       socket error queue to retrieve detailed information  about
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       the error; see IP_RECVERR in ip(4).
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       The  operation  of  sockets  is controlled by socket level
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       options.  These options  are  defined  in  <sys/socket.h>.
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       Setsockopt(2)  and  getsockopt(2)  are used to set and get
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       options, respectively.
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RETURN VALUES
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       -1 is returned if an error occurs;  otherwise  the  return
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       value is a descriptor referencing the socket.
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ERRORS
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       EPROTONOSUPPORT
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               The protocol type or the specified protocol is not
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               supported within this domain.
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       EMFILE  There are too many open files.
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       EACCES  Permission  to  create  a  socket of the specified
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               type and/or protocol is denied.
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       ENOBUFS or ENOMEM
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               Insufficient memory is available.  The socket can-
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               not  be  created  until  sufficient  resources are
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               freed.
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       EINVAL  Unknown protocol, or protocol  family  not  avail-
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               able.

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