ZeroMQ's IPv6 support isn't enabled by default, resulting in
"No such device" errors when attempting to listen on an IPv6
address. This change adds a ipv6 option to the ZeroMQ module
and enables it by default. Further, adds a test configuring
everything to listen on IPv6 ::1 as well, and one test to provoke
the original error. This also regularizes some error messages.
The addr_to_uri() calls weren't actually needed, but they apparently do
not hurt and the result is easier on the eyes, so use them :-)
The ZeroMQ heuristic for "ready to publish" is to create an unique and
ephemeral subscription using the XSUB socket and observe it arrive on the
XPUB socket. At this point, visibility into other node's subscriptions
is provided.
Due to prefix matching, worker-1's node_topic() also matched worker-10,
worker-11, etc. Suffix the node topic with a `.`. The original implementation
came from NATS, where subjects are separated by `.`.
Adapt nodeid_topic() for consistency.
It is not safe to use the same socket from different threads, but the
current code used the xsub socket directly from the main thread (to setup
subscriptions) and from the internal thread for polling and reading.
Leverage the PAIR socket already in use for forwarding publish operations
to the internal thread also for subscribe and unsubscribe.
The failure mode is/was a bit annoying. Essentially, closing of the
context would hang indefinitely in zmq_ctx_term().
This is a cluster backend implementation using a central XPUB/XSUB proxy
that by default runs on the manager node. Logging is implemented leveraging
PUSH/PULL sockets between logger and other nodes, rather than going
through XPUB/XSUB.
The test-all-policy-cluster baseline changed: Previously, Broker::peer()
would be called from setup-connections.zeek, causing the IO loop to be
alive. With the ZeroMQ backend, the IO loop is only alive when
Cluster::init() is called, but that doesn't happen anymore.
