Problem: Heartbeating not supported by RADIO/DISH

[jean-airoldie]

Related to #3550

Issue description

Setting a ZMQ_HEARTBEAT_IVL to either (or both) DISH or RADIO eventually causes the DISH socket to no longuer receive messages over TCP.

Environment

• libzmq version (commit hash if unreleased): fcf828d
• OS: Fedora 29

Minimal test code / Steps to reproduce the issue

• Create and bind a RADIO socket to a TCP endpoint. Set ZMQ_HEARTBEAT_IVL on the RADIO socket to any reasonable value.
• Create and connect a DISH socket to the bound endpoint. Set ZMQ_RCVTIMEO to something reasonable.
• Wait a bit for the connection to be established.
• Now send message from the RADIO socket and receive them from the DISH in a loop.

What's the actual result? (include assertion message & call stack if applicable)

The DISH socket will receive messages for a while, but eventually all recv calls
will return EAGAIN.

What's the expected result?

The DISH socket should always receive the messages coming from the RADIO socket.

[bluca]

Heartbeat is not implemented by the udp engine

[jean-airoldie]

I'll add some clarification, I was using TCP in my case. So I'm pretty sure this is a bug as opposed to a feature request.

Nevermind the RADIO and DISH sockets both use the udp_engine implementation, which does not yet support heatbeating, like bluca said.