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2019-12-14T22:19:25Z

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=== Passing file descriptors ===

<source lang="C">
#include <sys/socket.h>
#include <sys/types.h>
#include <sys/un.h>

#include <errno.h>
#include <error.h>
#include <stdlib.h>

static void sendfd(int socket, int fd)
{
char buf[CMSG_SPACE(sizeof(fd))];
memset(buf, 0, sizeof(buf));

struct msghdr msg = {};
msg.msg_iov = 0;
msg.msg_iovlen = 0;
msg.msg_control = buf;
msg.msg_controllen = sizeof(buf);

struct cmsghdr *cmsg = CMSG_FIRSTHDR(&msg);
cmsg->cmsg_level = SOL_SOCKET;
cmsg->cmsg_type = SCM_RIGHTS;
cmsg->cmsg_len = CMSG_LEN(sizeof(fd));

*((int *) CMSG_DATA(cmsg)) = fd;

msg.msg_controllen = cmsg->cmsg_len;

if (sendmsg(socket, &msg, 0) == -1)
error(EXIT_FAILURE, errno, "sendmsg()");
}

static int recvfd(int socket)
{
struct msghdr msg = {};
msg.msg_iov = 0;
msg.msg_iovlen = 0;

char buf[256];
msg.msg_control = buf;
msg.msg_controllen = sizeof(buf);

if (recvmsg(socket, &msg, 0) == -1)
error(EXIT_FAILURE, errno, "recvmsg()");

struct cmsghdr *cmsg = CMSG_FIRSTHDR(&msg);
unsigned char *data = CMSG_DATA(cmsg);
int fd = *((int *) data);
return fd;
}

int main(int argc, char *argv[])
{
int unix_fd[2] = {};
if (socketpair(AF_UNIX, SOCK_SEQPACKET, 0, unix_fd) == -1)
error(EXIT_FAILURE, errno, "socketpair(AF_UNIX)");

sendfd(unix_fd[0], 0);
int fd = recvfd(unix_fd[1]);

return 0;
}
</source>

[[Category:Programming]]
[[Category:C]]

UNIX sockets - Revision history

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