+/* CC0 license (public domain) - see LICENSE file for details */
+#include <ccan/fdpass/fdpass.h>
+#include <sys/socket.h>
+#include <errno.h>
+#include <string.h>
+
+bool fdpass_send(int sockout, int fd)
+{
+ /* From the cmsg(3) manpage: */
+ struct msghdr msg = { 0 };
+ struct cmsghdr *cmsg;
+ struct iovec iov;
+ char c = 0;
+ union { /* Ancillary data buffer, wrapped in a union
+ in order to ensure it is suitably aligned */
+ char buf[CMSG_SPACE(sizeof(fd))];
+ struct cmsghdr align;
+ } u;
+
+ msg.msg_control = u.buf;
+ msg.msg_controllen = sizeof(u.buf);
+ memset(&u, 0, sizeof(u));
+ cmsg = CMSG_FIRSTHDR(&msg);
+ cmsg->cmsg_level = SOL_SOCKET;
+ cmsg->cmsg_type = SCM_RIGHTS;
+ cmsg->cmsg_len = CMSG_LEN(sizeof(fd));
+ memcpy(CMSG_DATA(cmsg), &fd, sizeof(fd));
+
+ msg.msg_name = NULL;
+ msg.msg_namelen = 0;
+ msg.msg_iov = &iov;
+ msg.msg_iovlen = 1;
+ msg.msg_flags = 0;
+
+ /* Keith Packard reports that 0-length sends don't work, so we
+ * always send 1 byte. */
+ iov.iov_base = &c;
+ iov.iov_len = 1;
+
+ return sendmsg(sockout, &msg, 0) == 1;
+}
+
+int fdpass_recv(int sockin)
+{
+ /* From the cmsg(3) manpage: */
+ struct msghdr msg = { 0 };
+ struct cmsghdr *cmsg;
+ struct iovec iov;
+ int fd;
+ char c;
+ union { /* Ancillary data buffer, wrapped in a union
+ in order to ensure it is suitably aligned */
+ char buf[CMSG_SPACE(sizeof(fd))];
+ struct cmsghdr align;
+ } u;
+
+ msg.msg_control = u.buf;
+ msg.msg_controllen = sizeof(u.buf);
+
+ msg.msg_name = NULL;
+ msg.msg_namelen = 0;
+ msg.msg_iov = &iov;
+ msg.msg_iovlen = 1;
+ msg.msg_flags = 0;
+
+ iov.iov_base = &c;
+ iov.iov_len = 1;
+
+ if (recvmsg(sockin, &msg, 0) < 0)
+ return -1;
+
+ cmsg = CMSG_FIRSTHDR(&msg);
+ if (!cmsg
+ || cmsg->cmsg_len != CMSG_LEN(sizeof(fd))
+ || cmsg->cmsg_level != SOL_SOCKET
+ || cmsg->cmsg_type != SCM_RIGHTS) {
+ errno = -EINVAL;
+ return -1;
+ }
+
+ memcpy(&fd, CMSG_DATA(cmsg), sizeof(fd));
+ return fd;
+}