Blockchain's notificationDispatcher sends events to channels and these
channels must be read from. Unfortunately, regular service shutdown procedure
does unsubscription first (outside of the read loop) and only then drains the
channel. While it waits for unsubscription request to be accepted
notificationDispatcher can try pushing more data into the same channel which
will lead to a deadlock. Reading in the same method solves this, any number of
events can be pushed until unsub channel accepts the data.
See neo-project/neo#2390. Can't see it there? No wonder, that's why we have
this bug for a year and a half. Not critical, we don't care about versions,
but _very_ annoying.
It's not an ideal solution, but at least it solves the problem for
now. Caveats:
* consensus only needs one method, so it's mirrored to Blockchain
* rpcsrv uses core.* definition of the StateRoot (so technically it might as
well not have an internal Ledger), but it uses core already unfortunately
consensus.OnTransaction is a callback, so it can be called at any time.
We need to check whether service (and dBFT) is started before the
subsequent transaction handling like it is done inside the OnPayload
callback.
Notice that it makes the node accept Extensible payloads with any category
which is the same way C# node works. We're trusting Extensible senders,
improper payloads are harmless until they DoS the network, but we have some
protections against that too (and spamming with proper category doesn't differ
a lot).
It was broken somewhere between 2f490a3403 and
85ce207f40 leading to panic on watch only node:
2021-07-21T16:21:39.201+0200 INFO received Commit {"validator": 3}
panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x1 addr=0x28 pc=0xbcc59e]
goroutine 486 [running]:
github.com/nspcc-dev/neo-go/pkg/consensus.(*service).newBlockFromContext(0xc0001629a0, 0xc000308000, 0xc0010fa000, 0x2cb417800)
github.com/nspcc-dev/neo-go/pkg/consensus/consensus.go:664 +0xbe
github.com/nspcc-dev/dbft.(*Context).MakeHeader(...)
github.com/nspcc-dev/dbft@v0.0.0-20210302103605-cc75991b7cfb/context.go:270
github.com/nspcc-dev/dbft.(*DBFT).onCommit(0xc000308000, 0x138c998, 0xc000115110)
github.com/nspcc-dev/dbft@v0.0.0-20210302103605-cc75991b7cfb/dbft.go:487 +0x575
github.com/nspcc-dev/dbft.(*DBFT).OnReceive(0xc000308000, 0x138c998, 0xc000115110)
github.com/nspcc-dev/dbft@v0.0.0-20210302103605-cc75991b7cfb/dbft.go:251 +0xef5
github.com/nspcc-dev/neo-go/pkg/consensus.(*service).eventLoop(0xc0001629a0)
github.com/nspcc-dev/neo-go/pkg/consensus/consensus.go:312 +0x7d6
created by github.com/nspcc-dev/neo-go/pkg/consensus.(*service).Start
github.com/nspcc-dev/neo-go/pkg/consensus/consensus.go:262 +0xdc
In fact, nonce is correctly provided by dbft library (since Legacy), we just
need to use it here.
It's only used to sign/verify it and is not a part of the structure. It's
still neded in consensus.Payload though because that's the way dbft library
is.
It's not network-tied any more, network is only needed to
sign/verify. Unfortunately we still have to keep network in consensus data
structures because of dbft library interface.
