通过FIFO实现客户端服务器程序

在 TLPI 中看到这样的一个通过 FIFO 实现CS 架构的程序，手敲一遍。

文件 fifo_seqnum.h

#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>

#define SERVER_FIFO "/tmp/seqnum_sv"
#define CLIENT_FIFO_TEMPLATE "/tmp/seqnum_cl.%ld"
#define CLIENT_FIFO_NAME_LEN (sizeof(CLIENT_FIFO_TEMPLATE) + 20)

struct request
{
    pid_t pid;
    int seqLen;
};

struct response
{
    int seqNum;
};

文件 fifo_seqnum_server.c

#include <signal.h>
#include "fifo_seqnum.h"
#include <errno.h>
#include <stdlib.h>
#include <stdio.h>
#include <unistd.h>

int main()
{

    int serverFd, dummyFd, clientFd;
    char clientFifo[CLIENT_FIFO_NAME_LEN];
    struct request req;
    struct response resp;
    int seqNum = 0;

    umask(0);
    if (mkfifo(SERVER_FIFO, S_IRUSR | S_IWUSR | S_IWGRP) == -1 && errno != EEXIST)
    {
        exit(-1);
    }

    serverFd = open(SERVER_FIFO, O_RDONLY);
    if (serverFd == -1)
    {
        exit(-2);
    }

    dummyFd = open(SERVER_FIFO, O_WRONLY);
    if (dummyFd == -1)
    {
        exit(-3);
    }

    if (signal(SIGPIPE, SIG_IGN) == SIG_ERR)
    {
        exit(-4);
    }

    for(;;)
    {
        if (read(serverFd, &req, sizeof(struct request)) != sizeof(struct request))
        {
            fprintf(stderr, "Error reading\n");
            continue;
        }
        snprintf(clientFifo, CLIENT_FIFO_NAME_LEN, CLIENT_FIFO_TEMPLATE, (long)req.pid);
        clientFd = open(clientFifo, O_WRONLY);
        if (clientFd == -1)
        {
            fprintf(stderr, "Error openFifo\n");
            continue;
        }

        resp.seqNum = seqNum;

        if (write(clientFd, &resp, sizeof(struct response)) != sizeof(struct response))
        {
            fprintf(stderr, "Error write\n");
        }

        if (close(clientFd) == -1)
        {
            fprintf(stderr, "Error close\n");
        }

        seqNum += req.seqLen;
    }
    return 0;
}

文件 fifo_seqnum_client.c

#include <signal.h>
#include "fifo_seqnum.h"
#include <errno.h>
#include <stdlib.h>
#include <stdio.h>
#include <unistd.h>
#include <string.h>

static char clientFifo[CLIENT_FIFO_NAME_LEN];
static void removeFifo(void)
{
    unlink(clientFifo);
}

int main(int argc, char *argv[])
{

    int serverFd, clientFd;
    struct request req;
    struct response resp;

    if (argc > 1 && (strcmp(argv[1], "--help") == 0))
    {
        printf("%s [seq-len...]\n", argv[0]);
        exit(0);
    }

    umask(0);
    snprintf(clientFifo, CLIENT_FIFO_NAME_LEN, CLIENT_FIFO_TEMPLATE, (long)getpid());

    if (mkfifo(clientFifo, S_IRUSR | S_IWUSR | S_IWGRP) == -1 && errno != EEXIST)
    {
        exit(-1);
    }

    if (atexit(removeFifo) != 0)
    {
        exit(-2);
    }

    req.pid = getpid();
    req.seqLen = (argc > 1) ? atoi(argv[1]) : 1;

    serverFd = open(SERVER_FIFO, O_WRONLY);
    if (serverFd == -1)
    {
        exit(-2);
    }

    if (write(serverFd, &req, sizeof(struct request)) != sizeof(struct request))
    {
        fprintf(stderr, "Error write\n");
        exit(-3);
    }

    clientFd = open(clientFifo, O_RDONLY);
    if (clientFd == -1)
    {
        fprintf(stderr, "Error openFifo\n");
        exit(-4);
    }

    if (read(clientFd, &resp, sizeof(struct response)) != sizeof(struct response))
    {
        fprintf(stderr, "Error reading\n");
        exit(-5);
    }

    printf("%d\n", resp.seqNum);

    return 0;
}

实现的颇为巧妙，通过两个 FIFO 就读写数据。