SOCKETPAIR(3P)

💖 SOCKETPAIR(3P) — bestie edition 💖

okay so this one lives in the POSIX Programmer's Manual, and it's giving very much "the standard says so" energy. ✨

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🌸 PROLOG 🌸

real talk first, bestie: this manual page is part of the POSIX Programmer's Manual. The Linux implementation of this interface may differ — so like, consult the corresponding Linux manual page for the tea on Linux behavior — or honestly the interface may just not be implemented on Linux at all. 🙈 Not every glow-up is available everywhere, iykyk.

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👑 NAME 👑

socketpair — create a pair of connected sockets. two sockets. connected. a little duo. iconic. 💅

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✨ SYNOPSIS ✨

#include <sys/socket.h>

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

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🦋 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 — twins, no cap, matching outfits fr fr. 👯

The file descriptors used in referencing the created sockets shall be returned in socket_vector[0] and socket_vector[1]. And the file descriptors shall be allocated as described in Section 2.14, File Descriptor Allocation. 📚

So the socketpair() function takes these arguments, lemme introduce you:

• 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. (zero = "you pick bestie, I trust you" 🫶)
• 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. (chaotic. unreliable. we love her anyway. 😭)
• 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. (aka: not our call, that's the system's business 💅)

The process may need to have appropriate privileges to use the socketpair() function or to create some sockets. so like, sometimes you gotta have the ✨permissions✨. main character access only.

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🎀 RETURN VALUE 🎀

Upon successful completion, this function shall return 0. otherwise, -1 shall be returned and errno set to indicate the error, no file descriptors shall be allocated, and the contents of socket_vector shall be left unmodified. (so if it flops, it flops clean — nothing half-done, periodt.)

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💀 ERRORS 💀

The socketpair() function shall fail if:

• EAFNOSUPPORT — The implementation does not support the specified address family. 🙅
• EMFILE — All, or all but one, of the file descriptors available to the process are currently open.
• 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. (so like, the rest is lore, not law ✨)

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🍓 EXAMPLES 🍓

None. (literally nothing. the void. the silence. 😭)

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🧚 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. (go read those pages too bestie, this one can't carry the whole syllabus 🫶)

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

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💜 RATIONALE 💜

None. (no thoughts, head empty, but make it standards-compliant 🌸)

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🔥 FUTURE DIRECTIONS 🔥

None. (she's not going anywhere. she's stable. we stan consistency. 👑)

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💅 SEE ALSO 💅

• Section 2.14, File Descriptor Allocation
• socket()

The Base Definitions volume of POSIX.1‐2017, <sys_socket.h>

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⭐ COPYRIGHT ⭐

Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1-2017, Standard for Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 7, 2018 Edition, Copyright (C) 2018 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 .

Any typographical or formatting errors that appear in this page are most likely to have been introduced during the conversion of the source files to man page format. To report such errors, see https://www.kernel.org/doc/man-pages/reporting_bugs.html .

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and that's the whole page, bestie!! 🫶 this absolute banger of a page is brought to you by IEEE/The Open Group, 2017, and yes the title really is SOCKETPAIR(3P) — go forth and pair those sockets, you've got this 💖✨