coap_io.c: Add in support for getting state of internal file descriptors

[mrdeep1]

Add in a new function coap_io_get_fds() to get the lists of (internal to libcoap) file descriptors that are in a read or write pending state.

[mkicherer]

It looks like this only works if coap_io_process_with_fds_lkd is called before as this will set ctx->num_sockets. In my case (libcoapy under Windows), ctx->num_sockets is always zero and coap_io_get_fds will not return any fds.

This seems to work for me:

  coap_endpoint_t *ep;
  LL_FOREACH(ctx->endpoint, ep) {
    if (ep->sock.flags & (COAP_SOCKET_WANT_READ|COAP_SOCKET_WANT_ACCEPT)) {
      if (!coap_add_fd(ep->sock.fd, read_fds, have_read_fds, max_read_fds))
        return 0;
    }
    if (ep->sock.flags & (COAP_SOCKET_WANT_WRITE|COAP_SOCKET_WANT_CONNECT)) {
      if (!coap_add_fd(ep->sock.fd, write_fds, have_write_fds, max_write_fds))
        return 0;
    }
  }

I am currently stuck with an other issue, so I cannot test it completely but it looks good so far.

[mkicherer]

Ah, I see you also made this change. I will pull the new commit.

[mkicherer]

I got my bug fixed and it works flawlessly with this commit. Thank you!