Method sendfile

src/posix/libevent/libevent_ssl_socket.cpp:817–920

Future<size_t> LibeventSSLSocketImpl::sendfile(
    int_fd fd,
    off_t offset,
    size_t size)
{
  // Optimistically construct a 'SendRequest' and future.
  Owned<SendRequest> request(new SendRequest(size));
  Future<size_t> future = request->promise.future();

  // Assign 'send_request' under lock, fail on error.
  synchronized (lock) {
    if (send_request.get() != nullptr) {
      return Failure("Socket is already sending");
    }
    std::swap(request, send_request);
  }

  // Duplicate the file descriptor because Libevent will take ownership
  // and control the lifecycle separately.
  //
  // TODO(josephw): We can avoid duplicating the file descriptor in
  // future versions of Libevent. In Libevent versions 2.1.2 and later,
  // we may use `evbuffer_file_segment_new` and `evbuffer_add_file_segment`
  // instead of `evbuffer_add_file`.
  Try<int_fd> dup = os::dup(fd);
  if (dup.isError()) {
    return Failure(dup.error());
  }

  // NOTE: This is *not* an `int_fd` because `libevent` requires a CRT
  // integer file descriptor, which we allocate and then use
  // exclusively here.
#ifdef __WINDOWS__
  int owned_fd = dup->crt();
  // The `os::cloexec` and `os::nonblock` functions do nothing on
  // Windows, and cannot be called because they take `int_fd`.
#else
  int owned_fd = dup.get();

  // Set the close-on-exec flag.
  Try<Nothing> cloexec = os::cloexec(owned_fd);
  if (cloexec.isError()) {
    os::close(owned_fd);
    return Failure(
        "Failed to set close-on-exec on duplicated file descriptor: " +
        cloexec.error());
  }

  // Make the file descriptor non-blocking.
  Try<Nothing> nonblock = os::nonblock(owned_fd);
  if (nonblock.isError()) {
    os::close(owned_fd);
    return Failure(
        "Failed to make duplicated file descriptor non-blocking: " +
        nonblock.error());
  }
#endif // __WINDOWS__