socketpair.c

#include <sys/types.h>
#include <sys/socket.h>
#include <stdio.h>

#define DATA1 "This is from An Introductory 4.3BSD Interprocess Communication Tutorial"
#define DATA2 "practice typing and learning C sockets"

/*
 * 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 communication 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\n", 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\n", buf);
        close(sockets[0]);

    }
}