TCP sockets remain open in CLOSE_WAIT state

Hi guys,

thanks for developing the awesome qpid_proton ruby gem, we're using it on daily basis!
However, recently we noticed following error in our server log:

Too many open files - socket(2) for "172.16.117.189" port 5672

After some research it turns out that qpid_proton process is having increasingly
more and more following file descriptors open:

$ lsof -ap 108533
ruby 108533 miha 116u IPv4 562438 0t0 TCP 172.16.117.189:53626->147.75.102.132:amqp (CLOSE_WAIT)
ruby 108533 miha 197u IPv4 561644 0t0 TCP 172.16.117.189:53630->147.75.102.132:amqp (CLOSE_WAIT)
ruby 108533 miha 311u IPv4 560657 0t0 TCP 172.16.117.189:53634->147.75.102.132:amqp (CLOSE_WAIT)
ruby 108533 miha 549u IPv4 565342 0t0 TCP 172.16.117.189:53642->147.75.102.132:amqp (CLOSE_WAIT)
ruby 108533 miha 576u IPv4 565122 0t0 TCP 172.16.117.189:53650->147.75.102.132:amqp (CLOSE_WAIT)
ruby 108533 miha 603u IPv4 565738 0t0 TCP 172.16.117.189:53654->147.75.102.132:amqp (CLOSE_WAIT)
ruby 108533 miha 630u IPv4 563021 0t0 TCP 172.16.117.189:53658->147.75.102.132:amqp (CLOSE_WAIT)
ruby 108533 miha 657u IPv4 568361 0t0 TCP 172.16.117.189:53662->147.75.102.132:amqp (CLOSE_WAIT)
ruby 108533 miha 666u IPv4 563027 0t0 TCP 172.16.117.189:53666->147.75.102.132:amqp (CLOSE_WAIT)
ruby 108533 miha 675u IPv4 567538 0t0 TCP 172.16.117.189:53670->147.75.102.132:amqp (CLOSE_WAIT)
ruby 108533 miha 684u IPv4 567998 0t0 TCP 172.16.117.189:53678->147.75.102.132:amqp (CLOSE_WAIT)
ruby 108533 miha 690u IPv4 574709 0t0 TCP 172.16.117.189:53686->147.75.102.132:amqp (CLOSE_WAIT)
ruby 108533 miha 693u IPv4 578725 0t0 TCP 172.16.117.189:53694->147.75.102.132:amqp (CLOSE_WAIT)
ruby 108533 miha 696u IPv4 576840 0t0 TCP 172.16.117.189:53698->147.75.102.132:amqp (CLOSE_WAIT)
ruby 108533 miha 699u IPv4 577819 0t0 TCP 172.16.117.189:53702->147.75.102.132:amqp (CLOSE_WAIT)
ruby 108533 miha 702u IPv4 582192 0t0 TCP 172.16.117.189:53710->147.75.102.132:amqp (CLOSE_WAIT)
ruby 108533 miha 705u IPv4 582861 0t0 TCP 172.16.117.189:53714->147.75.102.132:amqp (CLOSE_WAIT)
ruby 108533 miha 708u IPv4 577363 0t0 TCP 172.16.117.189:53718->147.75.102.132:amqp (CLOSE_WAIT)
ruby 108533 miha 711u IPv4 578175 0t0 TCP 172.16.117.189:53722->147.75.102.132:amqp (CLOSE_WAIT)
ruby 108533 miha 714u IPv4 587172 0t0 TCP 172.16.117.189:53730->147.75.102.132:amqp (CLOSE_WAIT)
ruby 108533 miha 717u IPv4 584387 0t0 TCP 172.16.117.189:53734->147.75.102.132:amqp (CLOSE_WAIT)
...

I think the CLOSE_WAIT status of file descriptor indicates that the TCP
connection has already been closed, but the file descriptor wasn't closed.
After 9 hours or so there are enough of such file descriptors for OS to
complain about it.

We did all we could to close connections gracefully:

connection.container.stop
connection.close
connection = nil

but nothing seems to help. A simple but expensive workaround is to manually invoke Ruby's garbage collection,
but ideally `connection.close` would close the file descriptor.

May I kindly ask you to look at this?

Thank you and Best Regards,
Miha

PS: The error occurs both on Ubuntu 16.04 and RHEL 7.4
PS2: The error occurs both on qpid_proton 0.19.0 and 0.21.0