4.3BSD/usr/doc/ps1/07.ipctut/socketpair.c

.\" Copyright (c) 1986 Regents of the University of California.
.\" All rights reserved.  The Berkeley software License Agreement
.\" specifies the terms and conditions for redistribution.
.\"
.\"	@(#)socketpair.c	6.2 (Berkeley) 5/8/86
.\"
#include <sys/types.h>
#include <sys/socket.h>
#include <stdio.h>

#define DATA1 "In Xanadu, did Kublai Khan . . ."
#define DATA2 "A stately pleasure dome decree . . ."

/*
 * This program creates a pair of connected sockets then forks and
 * communicates over them.  This is very similar to communication with pipes,
 * however, socketpairs are two-way communications objects. Therefore I can
 * send messages in both directions. 
 */

main()
{
	int sockets[2], child;
	char buf[1024];

	if (socketpair(AF_UNIX, SOCK_STREAM, 0, sockets) < 0) {
		perror("opening stream socket pair");
		exit(1);
	}

	if ((child = fork()) == -1)
		perror("fork");
	else if (child) {	/* This is the parent. */
		close(sockets[0]);
		if (read(sockets[1], buf, 1024, 0) < 0)
			perror("reading stream message");
		printf("-->%s\en", buf);
		if (write(sockets[1], DATA2, sizeof(DATA2)) < 0)
			perror("writing stream message");
		close(sockets[1]);
	} else {		/* This is the child. */
		close(sockets[1]);
		if (write(sockets[0], DATA1, sizeof(DATA1)) < 0)
			perror("writing stream message");
		if (read(sockets[0], buf, 1024, 0) < 0)
			perror("reading stream message");
		printf("-->%s\en", buf);
		close(sockets[0]);
	}
}