Socketpair sample code (UNIX only)

The following example illustrates the use of socketpairs, which are a slight generalization of pipes used for two-way stream communication. Because socketpairs are an extension of pipes, their use resembles that of pipes rather than that of standard UNIX domain sockets. For more information, see ``Socketpairs (UNIX domain only)''.

Note that the header files <sys/socket.h> and <sys/types.h> are required in this program. The constants AF_UNIX and SOCK_STREAM are defined in <sys/socket.h>, which in turn requires the file <sys/types.h> for some of its definitions.

Using Socketpairs

#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,
 * this program 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]);
    }
}