Function RecvFile

internal/cmsg/cmsg.go:44–115

RecvFile waits for a file descriptor to be sent over the given AF_UNIX socket. The file name of the remote file descriptor will be recreated locally (it is sent as non-auxiliary data in the same payload).

(socket *os.File)

// socket. The file name of the remote file descriptor will be recreated
// locally (it is sent as non-auxiliary data in the same payload).
func RecvFile(socket *os.File) (_ *os.File, Err error) {
	name := make([]byte, MaxNameLen)
	oob := make([]byte, oobSpace)

	sockfd := socket.Fd()
	var (
		n, oobn int
		err     error
	)

	for {
		n, oobn, _, _, err = unix.Recvmsg(int(sockfd), name, oob, unix.MSG_CMSG_CLOEXEC)
		if err != unix.EINTR {
			break
		}
	}

	if err != nil {
		return nil, os.NewSyscallError("recvmsg", err)
	}
	if n >= MaxNameLen || oobn != oobSpace {
		return nil, fmt.Errorf("recvfile: incorrect number of bytes read (n=%d oobn=%d)", n, oobn)
	}
	// Truncate.
	name = name[:n]
	oob = oob[:oobn]

	scms, err := unix.ParseSocketControlMessage(oob)
	if err != nil {
		return nil, err
	}

	// We cannot control how many SCM_RIGHTS we receive, and upon receiving
	// them all of the descriptors are installed in our fd table, so we need to
	// parse all of the SCM_RIGHTS we received in order to close all of the
	// descriptors on error.
	var fds []int
	defer func() {
		for i, fd := range fds {
			if i == 0 && Err == nil {
				// Only close the first one on error.
				continue
			}
			// Always close extra ones.
			_ = unix.Close(fd)
		}
	}()
	var lastErr error
	for _, scm := range scms {
		if scm.Header.Type == unix.SCM_RIGHTS {
			scmFds, err := unix.ParseUnixRights(&scm)
			if err != nil {
				lastErr = err
			} else {
				fds = append(fds, scmFds...)
			}
		}
	}