[zeromq-dev] Feature requests/thoughts for TCP transport

[Sergey Hripchenko]

I recently use zmq in some projects and although I pretty much like it and think it is awesome I feel that it needs some new features to be implemented for TCP transport to be widely used everywhere(in un-trusted and unreliable environment).
I will try to summarize them in one place and kindly ask You(persons developing this product) to comment on each feature:
•       Whenever it fits in zmq framework/philosophy?
•       Is it hard to implement?
•       Is it could be implemented (or could be planned to be implemented)? And in what release? (or how many releases away from now?)
•       Will you approve and merge it if someone makes a patch? For what release?

1.        zmq->socket(*)->setsockopt(ZMQ_TCP_KEEPALIVE) on both (server and client) ends for fault tolerant connections:
(we also need KEEPALIVE_IDLE, KEEPALIVE_INTVL, KEEPALIVE_CNT to properly configure it).
Without it for example zmq->socket(SUB)->connect(tcp://) will not reconnect and will hung forever if the remote side silently falls off at some point after the successful connect and the PUB server socket connected to this endpoint will be closed while the server is still off-line.
2.        zmq->socket(*)->setsockopt(ZMQ_TCP_MAX_PEERS, int) before zmq->socket(*)->bind(tcp://) to preserve server resources in case of evil while(true){connect()}; attack or bug in the code
3.        zmq->socket(*)->setsockopt(ZMQ_TCP_MAX_PEERS_BY_IP, int) before zmq->socket(*)->bind(tcp://) to limit impact of DDoS like situations
4.        multiple zmq->socket(*)->setsockopt(ZMQ_TCP_ACCEPT_FROM, cidr) before/after zmq->socket(*)->bind(tcp://) to allow zmq->socket(*)->accept() connections from only trusted ips.
(no filtering by default)
5.        zmq->socket(*)->setsockopt(ZMQ_TCP_AUTH_TOKEN, string) on server and client sides for peer authentication…. This is though… it breaks protocol compatibility…
a.        weak but easy to add: client will send this token(or nothing by default) in connect packet. Server will match it if configured(or skip this check by default)
b.        sufficient: client asks for random SALT in connect phase, then sends his md5(SALT, ZMQ_TCP_AUTH_TOKEN) in 2nd connect packet. Server matches it with saved SALT and his ZMQ_TCP_AUTH_TOKEN.
6.        zmq->socket(*)->disconnect(tcp://connstring) as  the opposite to zmq->socket(*)->connect(tcp://connstring)

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