This is more efficient since broadcasting about other peers is
strictly redundant. Any change to the peers will be broadcast by
those peers anyway. And SendAllGossipDown takes care of informing new
peers about others on first connect, and periodic gossip take care of
missed broadcasts.
The only reason we did broadcast about the remote peer is to reduce
the liklihood of UnknownPeerError and the associated throwing away of
gossip. This was always a bit of kludge, and is no longer necessary
since UnknownPeerError is gone.
Now peers only ever broadcast information about themselves. Which,
unlike information about other peers, is always authorative and most
up-to-date. Which is nice.
when encountering an unknown peer in received gossip, rather than
ignoring the entire gossip we create a placeholder Peer. This has
version 0 and uid 0, which means it will be replaced by any complete
peer information subsequently received via gossip.
This was missing.
There are two parts to this change:
1. updating the Peers.byName mapping when HasShortID changed (in
addition to the existing update on ShortID change). We need to be
careful about the sequencing here - both ShortID and HasShortID must
be set between the calls to deleteByShortID and addByShortID, since
the former is meant to delete the existing entry (hence use the old
values) and the latter add the new entry (hence use the new values).
2. update a peer when the received info has the same version and UID
but the current record has HasShortID=false, and the received info has
HasShortID=true. This caters for the case where we receive an update
about a weave 1.2+ peer first via a pre-1.2 peer (which does not
transmit ShortIDs, and always sets HasShortID=false) and subsequently
via a 1.2+ peer. The former update will force us to communicate with
that peer over the 'sleeve' overlay. We want to accept the latter
update, even though the version is the same, in order to update the
ShortID and HasShortID, so we can switch to fastdp.
Fixes#1731.
We need Connection.Shutdown to be non-blocked, and the way we achieved
this is by spawning a goroutine. However, there can be a potentially
unbounded number of Connection.Shutdown invocations. For example, if
the TCP connection has gone bad then any Connection.SendProtocolMsg
invocation will end up invoking Connection.Shutdown. There can be many
such invocations until the Connection has been removed from the
various data structures (e.g. LocalPeer.connections and
GossipSender.senders). Hence we can end up with with an unbounded
number of spawned goroutines.
To fix this, we introduce a one-element error channel on the
connection. Connection.Shutdown does a non-blocking send on that, and
the Connection.actorLoop reads from it and terminates.
This will throw away all but the first error encountered, but that is
fine and not much different from what was happening before (where we'd
throw away all but one of the errors encountered).
The same piece of GossipData can be shared and subject to different
Merge operations. We either need to copy the data when we share it, or
create copies on modification, i.e. copy-on-write.
We choose the latter, since it is more efficient and there is just one
mutating operation.
Fixes#1697.
The deadlock described for SendProtocolMsg (if it was going via the
actor) cannot occur since all sending of broadcasts and gossip by
LocalPeer is mediated by GossipSenders, the interaction with which is
non-blocking.
This is mostly a matter of moving some files, changing package names,
changing some imports, and changing some type references.
We duplicate the odd constant & global var, and the intmac/macint
functions, since neither 'router' or 'mesh' nor, really,' common' are
a natural home for them.
Matthias Radestock