sockpair02.cpp

//
// Created by jxq on 19-8-10.
//

//
// Created by jxq on 19-8-10.
//

// socket编程 17

#include <iostream>
#include <sys/types.h>
#include <sys/socket.h>
#include <stdio.h>
#include <sys/un.h>
#include <unistd.h>
#include <stdlib.h>
#include <sys/stat.h>
#include <fcntl.h>

using namespace std;
// https://blog.csdn.net/y396397735/article/details/50684558

#define ERR_EXIT(m) \
        do \
        { \
            perror(m); \
            exit(EXIT_FAILURE); \
        } while(0);


// https://www.cnblogs.com/mickole/articles/3204406.html
void send_fd(int sock_fd, int send_fd)
{
    int ret;
    struct msghdr msg;
    struct cmsghdr *p_cmsg;
    struct iovec vec;
    char cmsgbuf[CMSG_SPACE(sizeof(send_fd))];  // 整个结构体的大小
    int *p_fds;
    char sendchar = 0;

    msg.msg_control = cmsgbuf;
    msg.msg_controllen = sizeof(cmsgbuf);

    p_cmsg = CMSG_FIRSTHDR(&msg);   // CMSG_FIRSTHDR宏可以得到首个 cmsghdr 结构体的指针
    p_cmsg->cmsg_level = SOL_SOCKET;
    p_cmsg->cmsg_type = SCM_RIGHTS;
    p_cmsg->cmsg_len = CMSG_LEN(sizeof(send_fd));

    // 传入结构体指针 p_cmsg ，宏CMSG_DATA 可以得到准备存放send_fd 的位置指针，将send_fd 放进去
    p_fds = (int *)CMSG_DATA(p_cmsg);
    *p_fds = send_fd; // 通过传递辅助数据的方式传递文件描述符

    msg.msg_name = NULL;
    msg.msg_namelen = 0;
    msg.msg_iov = &vec;
    msg.msg_iovlen = 1; // 主要目的不是传递数据，故只传1个字符
    msg.msg_flags = 0;

    vec.iov_base = &sendchar;
    vec.iov_len = sizeof(sendchar);

    ret = sendmsg(sock_fd, &msg, 0);

    if (ret != 1)
        ERR_EXIT("sendmsg");
}

int recv_fd(const int sock_fd)
{
    int ret;
    struct msghdr msg;
    char recvchar;
    struct iovec vec;
    int recv_fd;

    char cmsgbuf[CMSG_SPACE(sizeof(recv_fd))];
    struct cmsghdr *p_cmsg;
    int *p_fd;

    vec.iov_base = &recvchar;
    vec.iov_len = sizeof(recvchar);

    msg.msg_name = NULL;
    msg.msg_namelen = 0;
    msg.msg_iov = &vec;
    msg.msg_iovlen = 1;
    msg.msg_control = cmsgbuf;
    msg.msg_controllen = sizeof(cmsgbuf);
    msg.msg_flags = 0;

    p_fd = (int *)CMSG_DATA(CMSG_FIRSTHDR(&msg));
    *p_fd = -1;

    ret = recvmsg(sock_fd, &msg, 0);
    if (ret != 1)
        ERR_EXIT("recvmsg");

    p_cmsg = CMSG_FIRSTHDR(&msg);   // 首个cmsghdr地址
    if (p_cmsg == NULL)
        ERR_EXIT("no passed fd");


    p_fd = (int *)CMSG_DATA(p_cmsg);    // 文件描述符
    recv_fd = *p_fd;
    if (recv_fd == -1)
        ERR_EXIT("no passed fd");

    return recv_fd;
}

int main(int argc, char** argv)
{
    int socketfd[2];
    int r = socketpair(AF_UNIX, SOCK_STREAM, 0, socketfd);

    if (r < 0)
    {
        ERR_EXIT("socketpair");
    }

    pid_t pid = fork();
    if (pid == -1)
    {
        ERR_EXIT("fork");
    }
    if (pid == 0)
    {
        int val = 0;
        close(socketfd[0]);
        int fd = recv_fd(socketfd[1]);
        char buf[1024] = {0};
        read(fd, buf, sizeof buf);
        printf("buf =  %s\n", buf);
    }
    else
    {
        close(socketfd[1]);
        int fd;
        fd = open("/home/jxq/CLionProjects/NetworkProgramming/text.txt", O_RDONLY);
        if (fd == -1)
        {
            ERR_EXIT("open");
        }
        send_fd(socketfd[0], fd);
    }
    return 0;
}