svmsg/svmsg_file_client.c

This is svmsg/svmsg_file_client.c (Listing 46-9, page 960), 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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Function list (Bold in this list means a function is not static)

#include "svmsg_file.h"

static int clientId;
static void
removeQueue(void)
{
    if (msgctl(clientId, IPC_RMID, NULL) == -1)
        errExit("msgctl");
}
int
main(int argc, char *argv[])
{
    struct requestMsg req;
    struct responseMsg resp;
    int serverId, numMsgs;
    ssize_t msgLen, totBytes;

    if (argc != 2 || strcmp(argv[1], "--help") == 0)
        usageErr("%s pathname\n", argv[0]);

    if (strlen(argv[1]) > sizeof(req.pathname) - 1)
        cmdLineErr("pathname too long (max: %ld bytes)\n",
                (long) sizeof(req.pathname) - 1);

    /* Get server's queue identifier; create queue for response */

    serverId = msgget(SERVER_KEY, S_IWUSR);
    if (serverId == -1)
        errExit("msgget - server message queue");

    clientId = msgget(IPC_PRIVATE, S_IRUSR | S_IWUSR | S_IWGRP);
    if (clientId == -1)
        errExit("msgget - client message queue");

    if (atexit(removeQueue) != 0)
        errExit("atexit");

    /* Send message asking for file named in argv[1] */

    req.mtype = 1;                      /* Any type will do */
    req.clientId = clientId;
    strncpy(req.pathname, argv[1], sizeof(req.pathname) - 1);
    req.pathname[sizeof(req.pathname) - 1] = '\0';
                                        /* Ensure string is terminated */

    if (msgsnd(serverId, &req, REQ_MSG_SIZE, 0) == -1)
        errExit("msgsnd");

    /* Get first response, which may be failure notification */

    msgLen = msgrcv(clientId, &resp, RESP_MSG_SIZE, 0, 0);
    if (msgLen == -1)
        errExit("msgrcv");

    if (resp.mtype == RESP_MT_FAILURE) {
        printf("%s\n", resp.data);      /* Display msg from server */
        exit(EXIT_FAILURE);
    }

    /* File was opened successfully by server; process messages
       (including the one already received) containing file data */

    totBytes = msgLen;                  /* Count first message */
    for (numMsgs = 1; resp.mtype == RESP_MT_DATA; numMsgs++) {
        msgLen = msgrcv(clientId, &resp, RESP_MSG_SIZE, 0, 0);
        if (msgLen == -1)
            errExit("msgrcv");

        totBytes += msgLen;
    }

    printf("Received %ld bytes (%d messages)\n", (long) totBytes, numMsgs);

    exit(EXIT_SUCCESS);
}

 

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