socket

Purpose

     Creates  an  endpoint  for communication  and  returns  a
     descriptor.

Library

     Sockets Library (libsock.a)

Syntax

     #include <sys/types.h>
     #include <sys/socket.h>

     int socket  (af, type, protocol)
     int af, type, protocol;

Description

     The socket  subroutine creates  an endpoint  for communi-
     cation and returns a socket descriptor.

     The af  parameter specifies an address  format with which
     addresses specified in later  socket operations should be
     interpreted.    These   formats   are  defined   in   the
     sys/socket.h header file.  The formats are:

     AF_UNIX   AIX path names
     AF_INET   ARPA Internet addresses.

     The value  of the type parameter  specifies the semantics
     of communication.  AIX supports these types:

     SOCK_STREAM   Provides  sequenced,  two-way byte  streams
                   with a  transmission mechanism  for out-of-
                   band data.
     SOCK_DGRAM    Provides      datagrams,     which      are
                   connectionless messages of  a fixed maximum
                   length (usually small).

     The protocol parameter specifies a particular protocol to
     be used  with the socket.   In most cases, a  single pro-
     tocol exists to support a  particular socket type using a
     given  address format.   When many  protocols exist,  you
     must specify  a particular protocol.  Use  the number for
     the communication domain in which the communication takes
     place.

     The  different types  of sockets  available are  used for
     different  purposes.   SOCK_DGRAM sockets  allow  sending
     datagrams to  correspondents named in send  socket calls.

     Programs can also receive  datagrams via sockets by using
     the recv subroutines.

     SOCK_STREAM  sockets  are  full-duplex byte  streams.   A
     stream socket  must be connected  before any data  may be
     sent or received  on it.  Create a  connection to another
     socket with the connect routine.  Once connected, use the
     read and write system calls, or the send and recv subrou-
     tines to transfer data.  Issue the close system call when
     a session is finished.  Use the send and recv subroutines
     for out-of-band data.

     SOCK_STREAM  communications  protocols  are  designed  to
     prevent the loss  or duplication of data.  If  a piece of
     data for which the peer  protocol has buffer space cannot
     be successfully transmitted within a reasonable period of
     time, the  connection is  broken.  When this  occurs, the
     socket routines indicate an error  with a return value of
     -1 and with ETIMEDOUT as the specific code written to the
     global variable  errno.  If a  process sends on  a broken
     stream,  a  SIGPIPE  signal is  raised.   Processes  that
     cannot handle the signal terminate.

     When  out-of-band  data arrives  on  a  socket, a  SIGURG
     signal is sent  to the process group.   The process group
     associated  with a  socket  may  be read  or  set by  the
     SIOCGPGRP ioctl  operation or the SIOCSPGRP  ioctl opera-
     tion.  If you  want to receive a signal on  any data, use
     both the SIOCSPGRP and  FIOASYNC ioctl operations.  These
     ioctl operations are defined in the bsd/sys/ioctl.h file.

     Sockets can be set to either blocking or non-blocking I/O
     mode.  The  FIONBIO ioctl operation is  used to determine
     this mode.   When FIONBIO  is set,  the socket  is marked
     non-blocking.  If a read is tried and the desired data is
     not available, the  socket does not wait for  the data to
     become available, but returns  immediately with the error
     code EWOULDBLOCK.  When FIONBIO is not set, the socket is
     in blocking mode.   In this mode, if a read  is tried and
     the desired  data is  not available, the  calling process
     waits for the data.

     Similarly, when writing, if FIONBIO is set and the output
     queue is full, an attempt  to write causes the process to
     return immediately with an error code of EWOULDBLOCK.

     The operation  of sockets  is controlled by  socket level
     options.  The  getsockopt and setsockopt  subroutines are
     used to get  and set these options, which  are defined in
     the sys/socket.h file.   See "getsockopt, setsockopt" for
     information on how to use these options.

Return Value

     Upon successful completion, a descriptor referring to the
     socket is returned.  If the socket routine fails, a value
     of  -1 is  returned, and  errno  is set  to indicate  the
     error.

Diagnostics

     The subroutine fails if one  or more of the following are
     true:

     EAFNOSUPPORT      The addresses in  the specified address
                       family cannot be used with this socket.

     ESOCKNOSUPPORT    The  socket  in the  specified  address
                       family is not supported.

     EMFILE            The  per-process  descriptor  table  is
                       full.

     ENOBUFS           Insufficient  resources were  available
                       in the system to complete the call.

Related Information

     In  this  book:   "ioctl,"  "select,"  "accept,"  "bind,"
     "connect,"   "getsockname,"   "getsockopt,   setsockopt,"
     "listen,"  "recv,  recvfrom,   recvmsg,"  "send,  sendto,
     sendmsg," "shutdown," and "socketpair."