NAME

       socketpair - create a pair of connected sockets

SYNOPSIS

       #include <sys/socket.h>

       int socketpair(int domain, int type, int protocol,
              int socket_vector[2]);

DESCRIPTION

       The  socketpair()  function shall create an unbound pair of connected sockets in a specified domain, of a
       specified type, under the protocol optionally specified by the protocol argument. The two  sockets  shall
       be  identical.  The  file  descriptors  used  in  referencing  the  created  sockets shall be returned in
       socket_vector[0] and socket_vector[1].

       The socketpair() function takes the following arguments:

       domain Specifies the communications domain in which the sockets are to be created.

       type   Specifies the type of sockets to be created.

       protocol
              Specifies a particular protocol to be used with the sockets. Specifying a  protocol  of  0  causes
              socketpair() to use an unspecified default protocol appropriate for the requested socket type.

       socket_vector
              Specifies a 2-integer array to hold the file descriptors of the created socket pair.

       The  type  argument  specifies the socket type, which determines the semantics of communications over the
       socket. The following socket types are defined; implementations may specify additional socket types:

       SOCK_STREAM
              Provides sequenced, reliable, bidirectional, connection-mode  byte  streams,  and  may  provide  a
              transmission mechanism for out-of-band data.

       SOCK_DGRAM
              Provides datagrams, which are connectionless-mode, unreliable messages of fixed maximum length.

       SOCK_SEQPACKET
              Provides  sequenced,  reliable,  bidirectional,  connection-mode transmission paths for records. A
              record can be sent using one or more output operations  and  received  using  one  or  more  input
              operations, but a single operation never transfers part of more than one record. Record boundaries
              are visible to the receiver via the MSG_EOR flag.

       If  the  protocol  argument  is  non-zero,  it  shall specify a protocol that is supported by the address
       family. If the protocol argument is zero, the default protocol for this address family and type shall  be
       used. The protocols supported by the system are implementation-defined.

       The  process  may  need to have appropriate privileges to use the socketpair() function or to create some
       sockets.

RETURN VALUE

       Upon successful completion, this function shall return 0; otherwise, -1 shall be returned and  errno  set
       to indicate the error.

ERRORS

       The socketpair() function shall fail if:

       EAFNOSUPPORT

              The implementation does not support the specified address family.

       EMFILE No more file descriptors are available for this process.

       ENFILE No more file descriptors are available for the system.

       EOPNOTSUPP
              The specified protocol does not permit creation of socket pairs.

       EPROTONOSUPPORT

              The  protocol  is  not  supported  by  the address family, or the protocol is not supported by the
              implementation.

       EPROTOTYPE
              The socket type is not supported by the protocol.

       The socketpair() function may fail if:

       EACCES The process does not have appropriate privileges.

       ENOBUFS
              Insufficient resources were available in the system to perform the operation.

       ENOMEM Insufficient memory was available to fulfill the request.

       The following sections are informative.

EXAMPLES

       None.

APPLICATION USAGE

       The documentation for specific address families specifies which protocols each address  family  supports.
       The documentation for specific protocols specifies which socket types each protocol supports.

       The  socketpair() function is used primarily with UNIX domain sockets and need not be supported for other
       domains.

RATIONALE

       None.

FUTURE DIRECTIONS

       None.

SEE ALSO

       socket() , the Base Definitions volume of IEEE Std 1003.1-2001, <sys/socket.h>

COPYRIGHT

       Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2003 Edition,
       Standard for Information Technology -- Portable Operating System Interface (POSIX), The Open  Group  Base
       Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of Electrical and Electronics Engineers,
       Inc  and  The  Open Group. In the event of any discrepancy between this version and the original IEEE and
       The Open Group Standard, the original IEEE and The Open Group  Standard  is  the  referee  document.  The
       original Standard can be obtained online at http://www.opengroup.org/unix/online.html .

IEEE/The Open Group                                   2003                                         SOCKETPAIR(P)