ZeroMQ: REQ/REP with large messages

Question

I am trying to send large messages ( 300 MB ) over a REP-socket.
There are multiple clients, each connecting to the server via a REQ-socket. The server creates a dedicated socket for every client, waits for the request ( containing an identifier ) and sends the message in two parts using ZMQ_SENDMORE:

1. metadata (~ 1 KB)
2. data (~ 300 MB)

After that the REP-socket is immediately closed. The Context()-instance is then closed in a parent thread. ZMQ_LINGER time of the socket is left at default ( infinite ). Sometimes the metadata is sent, but not the image data.
I traced the calls within ZeroMQ and found that the internal (windows) socket is closed before the message data has been sent to the network. I thought that zmq_term() would block as long as there are unsent messages in the queue.
As a workaround I changed the clients to send another request message after receiving the data as an acknowledgement. This works quite well, but I'm not quite sure if I have addressed the fundamental problem.

The ZeroMQ version is 4.0.4. I am using the C++ bindings. Server and clients all run on Windows ( 7 and 10 ).

Answer 1

I know that this is NOT the answer you want, but I experienced something similar with ZeroMQ on Linux. The underlying Linux socket closed and some messages never made it through.

In my use case, I hold the server open until the user gives me some keyboard input. It's a hack, but for my use case, it gives me what I want.

You can also sleep for a second or two before you close the socket. Once again, not pretty, but it might be a quick fix until this gets patched.

Edited to add: I am also sending multi-part messages and one of my message parts is fairly large (~200MB).