pipes/fifo_seqnum_server.c

This is pipes/fifo_seqnum_server.c (Listing 44-7, page 912), an example from the book, The Linux Programming Interface.

The source code file is copyright 2024, Michael Kerrisk, and is licensed under the GNU General Public License, version 3.

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#include <signal.h>
#include "fifo_seqnum.h"
int
main(int argc, char *argv[])
{
    int serverFd, dummyFd, clientFd;
    char clientFifo[CLIENT_FIFO_NAME_LEN];
    struct request req;
    struct response resp;
    int seqNum = 0;                     /* This is our "service" */

    /* Create well-known FIFO, and open it for reading */

    umask(0);                           /* So we get the permissions we want */
    if (mkfifo(SERVER_FIFO, S_IRUSR | S_IWUSR | S_IWGRP) == -1
            && errno != EEXIST)
        errExit("mkfifo %s", SERVER_FIFO);
    serverFd = open(SERVER_FIFO, O_RDONLY);
    if (serverFd == -1)
        errExit("open %s", SERVER_FIFO);

    /* Open an extra write descriptor, so that we never see EOF */

    dummyFd = open(SERVER_FIFO, O_WRONLY);
    if (dummyFd == -1)
        errExit("open %s", SERVER_FIFO);

    if (signal(SIGPIPE, SIG_IGN) == SIG_ERR)    errExit("signal");

    for (;;) {                          /* Read requests and send responses */
        if (read(serverFd, &req, sizeof(struct request))
                != sizeof(struct request)) {
            fprintf(stderr, "Error reading request; discarding\n");
            continue;                   /* Either partial read or error */
        }

        /* Open client FIFO (previously created by client) */

        snprintf(clientFifo, CLIENT_FIFO_NAME_LEN, CLIENT_FIFO_TEMPLATE,
                (long) req.pid);
        clientFd = open(clientFifo, O_WRONLY);
        if (clientFd == -1) {           /* Open failed, give up on client */
            errMsg("open %s", clientFifo);
            continue;
        }

        /* Send response and close FIFO */

        resp.seqNum = seqNum;
        if (write(clientFd, &resp, sizeof(struct response))
                != sizeof(struct response))
            fprintf(stderr, "Error writing to FIFO %s\n", clientFifo);
        if (close(clientFd) == -1)
            errMsg("close");

        seqNum += req.seqLen;           /* Update our sequence number */
    }
}

 

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