Caused by a race between adding the connection to our map and
receiving a topology gossip on it.
We remove the race by making AddConnection synchronous and invoking it
prior to entering the tcp receive loop.
Fixes#367.
Prior to the introduction of gossip, a tcp connection would not see
regular communication until it had been marked as 'established',
because the topology communication scheme would periodically send
'FetchAll' only after that. So in the absence of udp connectivity we'd
time out. The timeout could of course occur for other reasons, namely
disrupted tcp connectivity, but the combination of a timeout and 'not
established' pointed to a lack of udp connectivity as a likely
cause. So that's what we checked for.
In the new gossip-based topology communication, however, gossip (of
anything, not just topology) occurs as soon as we have tcp
connectivity. Therefore we will no longer encounter a timeout when
just udp connectivity is disrupted. Which makes our check invalid.
So instead we introduce a one-shot timer, created on handshake
completion and cancelled when we mark the connection as
'established'. When the timer fires, and the connection still hasn't
been established, we shut down the connection with an error indicating
lack of udp connectivity.
Instead of separately calculating routes to every individual peer,
carry out one calculation for routes to all peers. Same as unicast
routes except taking into account asymmetric connections.
Gossip layer to communicate topology between peers
Note that I have squashed over 100 commits from @bboreham and @rade into the three for this PR; you can see the original history at https://github.com/bboreham/weave/compare/add_gossip_full
When an update contains an older version of a peer we know about,
there is no point in including our better version in the "improved"
update, since we will have told our neighbours about that already and
any race conditions are taken care off by the periodic sending of the
complete topology.
- show complete call stack of failures (this does include some of the
testing machinery, but a) is simple, and b) is guaranteed to not
miss important stack frames)
- add helper to run test with a timeout
- add AssertEqualuint64
David Wragg