Function sendfd

module/src/main/cpp/utils.cpp:197–247

}

static int sendfd(int sockfd, int fd) {
	int data;
	struct iovec iov{};
	struct msghdr msgh{};
	struct cmsghdr *cmsgp;

	/* Allocate a char array of suitable size to hold the ancillary data.
	   However, since this buffer is in reality a 'struct cmsghdr', use a
	   union to ensure that it is suitably aligned. */
	union {
		char buf[CMSG_SPACE(sizeof(int))];
		/* Space large enough to hold an 'int' */
		struct cmsghdr align;
	} controlMsg{};

	/* The 'msg_name' field can be used to specify the address of the
	   destination socket when sending a datagram. However, we do not
	   need to use this field because 'sockfd' is a connected socket. */

	msgh.msg_name = nullptr;
	msgh.msg_namelen = 0;

	/* On Linux, we must transmit at least one byte of real data in
	   order to send ancillary data. We transmit an arbitrary integer
	   whose value is ignored by recvfd(). */

	msgh.msg_iov = &iov;
	msgh.msg_iovlen = 1;
	iov.iov_base = &data;
	iov.iov_len = sizeof(int);
	data = 12345;

	/* Set 'msghdr' fields that describe ancillary data */

	msgh.msg_control = controlMsg.buf;
	msgh.msg_controllen = sizeof(controlMsg.buf);

	/* Set up ancillary data describing file descriptor to send */

	cmsgp = reinterpret_cast<cmsghdr *>(msgh.msg_control);
	cmsgp->cmsg_level = SOL_SOCKET;
	cmsgp->cmsg_type = SCM_RIGHTS;
	cmsgp->cmsg_len = CMSG_LEN(sizeof(int));
	memcpy(CMSG_DATA(cmsgp), &fd, sizeof(int));

	/* Send real plus ancillary data */

	if (sendmsg(sockfd, &msgh, 0) == -1) return -1;

	return 0;
}

static int recvfd(int sockfd) {
	int data, fd;