SOCKETPAIR(3P)

PROLOG
This manual page is part of the POSIX Programmer's Manual. The Linux implementation of this interface may differ (consult the corresponding Linux manual page for details of Linux behavior), or the interface may not be implemented on Linux.

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 .