socketpair - create a pair of connected sockets
<sys/types.h> /* See NOTES */
int socketpair(int domain, int type, int protocol, int sv);
The socketpair() call creates an unnamed pair of connected sockets in the specified domain, of the specified type, and using the optionally specified protocol. For further details of these arguments, see socket(2).
The file descriptors used in referencing the new sockets are returned in sv and sv. The two sockets are indistinguishable.
On success, zero is returned. On error, -1 is returned, errno is set appropriately, and sv is left unchanged
On Linux (and other systems), socketpair() does not modify sv on failure. A requirement standardizing this behavior was added in POSIX.1-2008 TC2.
The specified address family is not supported on this machine.
The address sv does not specify a valid part of the process address space.
The per-process limit on the number of open file descriptors has been reached.
The system-wide limit on the total number of open files has been reached.
The specified protocol does not support creation of socket pairs.
The specified protocol is not supported on this machine.
POSIX.1-2001, POSIX.1-2008, 4.4BSD. socketpair() first appeared in 4.2BSD. It is generally portable to/from non-BSD systems supporting clones of the BSD socket layer (including System V variants).
On Linux, the only supported domains for this call are AF_UNIX (or synonymously, AF_LOCAL) and AF_TIPC (since Linux 4.12).
Since Linux 2.6.27, socketpair() supports the SOCK_NONBLOCK and SOCK_CLOEXEC flags in the type argument, as described in socket(2).
POSIX.1 does not require the inclusion of <sys/types.h>, and this header file is not required on Linux. However, some historical (BSD) implementations required this header file, and portable applications are probably wise to include it.
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