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#include <stdio.h>
#include <unistd.h>
#include <string.h>
#include <stdlib.h>
#include <fcntl.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <sys/wait.h>
int child_process(char *filename, int sock);
int parent_process(int sock);
void copy_data(int form, int to);
int main(int argc, char **argv) {
int socket[2];
int status;
if (argc != 2) {
printf("Usage: %s filename\n", argv[0]);
return 1;
}
// 创建一对匿名的已经连接的socket
// socket[0] 用于父进程
// socket[1] 用于子进程
if (socketpair(PF_UNIX, SOCK_STREAM, 0, socket)) {
perror("sockerpair error");
exit(1);
}
// 创建子进程
if (!fork()) {
// Child Process
close(socket[0]);
return child_process(argv[1], socket[1]);
}
// Parent Process
close(socket[1]);
parent_process(socket[0]);
// 回收子进程
wait(&status);
if (WEXITSTATUS(status))
fprintf(stderr, "child failed\n");
return 0;
}
// 子进程：发送文件描述符
int child_process(char *filename, int sock) {
int fd;
struct iovec iov[1] = {0};
struct msghdr msg = {0};
struct cmsghdr *cmsg;
int *fdptr;
union {
char buf[CMSG_SPACE(sizeof(int))];
struct cmsghdr align;
} u;
// 打开文件
if ((fd = open(filename, O_RDONLY)) < 0) {
perror("open");
return 1;
}
// 在使用SOCK_STREAM传递文件描述符时，必须发送或者接收至少一个字节的nonancillary数据。
iov[0].iov_base = filename;
iov[0].iov_len = strlen(filename) + 1;
// 通过SOCK_STREAM发送信息时，msg_name必须为NULL，msg_namelen必须为
msg.msg_name = NULL;
msg.msg_namelen = 0;
msg.msg_iov = iov;
msg.msg_iovlen = 1;
msg.msg_control = u.buf;
msg.msg_controllen = sizeof(u.buf);
cmsg = CMSG_FIRSTHDR(&msg);
cmsg->cmsg_level = SOL_SOCKET;
cmsg->cmsg_type = SCM_RIGHTS;
cmsg->cmsg_len = CMSG_LEN(sizeof(int));
// 初始化要发送的数据域,即将文件描述符拷贝到控制信息的末尾
fdptr = (int *) CMSG_DATA(cmsg);
memcpy(fdptr, &fd, sizeof(int));
if (sendmsg(sock, &msg, 0) != iov[0].iov_len) {
perror("sendmsg");
exit(1);
}
return 0;
}
// 父进程：接收文件描述符
int parent_process(int sock) {
struct msghdr msg = {0};
struct iovec iov[1] = {0};
struct cmsghdr *cmsg;
int *fdptr;
int fd;
char buf[80];
union {
char buf[CMSG_SPACE(sizeof(int))];
struct cmsghdr align;
} u;
// 为了接收文件名做准备
iov[0].iov_base = buf;
iov[0].iov_len = 80;
// 通过SOCK_STREAM接收信息时，msg_name必须为NULL，msg_namelen必须为
msg.msg_name = NULL;
msg.msg_namelen = 0;
msg.msg_iov = iov;
msg.msg_iovlen = 1;
msg.msg_control = u.buf;
msg.msg_controllen = sizeof(u.buf);
if (!recvmsg(sock, &msg, 0)) {
perror("recvmsg");
return 1;
}
cmsg = CMSG_FIRSTHDR(&msg);
if (!cmsg) {
perror("got NULL from CMSG_FIRSTHDR");
return 1;
}
if (cmsg->cmsg_level != SOL_SOCKET) {
fprintf(stderr, "expected SOL_SOCKET in cmsg: %d", cmsg->cmsg_level);
return 1;
}
if (cmsg->cmsg_type != SCM_RIGHTS) {
fprintf(stderr, "expected SCM_RIGHTS in cmsg: %d", cmsg->cmsg_type);
return 1;
}
if (cmsg->cmsg_len != CMSG_LEN(sizeof(int))) {
fprintf(stderr, "expected correct CMSG_LENin cmsg: %lu", cmsg->cmsg_len);
return 1;
}
fdptr = (int *)CMSG_DATA(cmsg);
if (!fdptr || *fdptr < 0) {
fprintf(stderr, "recieved invalid pointer or file descriptor");
return 1;
}
fd = *fdptr;
printf("Got file descriptor for '%s'\n", (char *)iov[0].iov_base);
printf("The file descriptor is %d\n", fd);
copy_data(fd, 1);
return 0;
}
// 将数据从文件描述符`from`中拷贝到`to`中，如果发送错误，则退出
void copy_data(int from, int to) {
char buf[1024];
int amount;
while ((amount = read(from, buf, sizeof(buf))) > 0) {
if (write(to, buf, amount) != amount) {
perror("write");
exit(1);
}
}
if (amount < 0) {
perror("read");
exit(1);
}
}
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