network: change the disconnect procedure

[roman-khimov]

We can still lock the (*Server).run with dead peers:

Feb 13 16:14:50 neo-go-node-2 neo-go[9448]: goroutine 40 [select, 871 minutes]:
Feb 13 16:14:50 neo-go-node-2 neo-go[9448]: github.com/CityOfZion/neo-go/pkg/network.(*TCPPeer).putPacketIntoQueue(0xc030ab5320, 0xc02f251f20, 0xc00af0dcc0, 0x18, 0x40, 0x100000000000000, 0xffffffffffffffff)
Feb 13 16:14:50 neo-go-node-2 neo-go[9448]: #11/go/src/github.com/CityOfZion/neo-go/pkg/network/tcp_peer.go:82 +0xf4
Feb 13 16:14:50 neo-go-node-2 neo-go[9448]: github.com/CityOfZion/neo-go/pkg/network.(*TCPPeer).EnqueueHPPacket(0xc030ab5320, 0xc00af0dcc0, 0x18, 0x40, 0x1367240, 0xc03090ef98)
Feb 13 16:14:50 neo-go-node-2 neo-go[9448]: #11/go/src/github.com/CityOfZion/neo-go/pkg/network/tcp_peer.go:124 +0x52
Feb 13 16:14:50 neo-go-node-2 neo-go[9448]: github.com/CityOfZion/neo-go/pkg/network.(*Server).iteratePeersWithSendMsg(0xc0000ca000, 0xc00af35800, 0xcb2a58, 0x0)
Feb 13 16:14:50 neo-go-node-2 neo-go[9448]: #11/go/src/github.com/CityOfZion/neo-go/pkg/network/server.go:720 +0x12a
Feb 13 16:14:50 neo-go-node-2 neo-go[9448]: github.com/CityOfZion/neo-go/pkg/network.(*Server).broadcastHPMessage(...)
Feb 13 16:14:50 neo-go-node-2 neo-go[9448]: #11/go/src/github.com/CityOfZion/neo-go/pkg/network/server.go:731
Feb 13 16:14:50 neo-go-node-2 neo-go[9448]: github.com/CityOfZion/neo-go/pkg/network.(*Server).run(0xc0000ca000)
Feb 13 16:14:50 neo-go-node-2 neo-go[9448]: #11/go/src/github.com/CityOfZion/neo-go/pkg/network/server.go:203 +0xee4
Feb 13 16:14:50 neo-go-node-2 neo-go[9448]: github.com/CityOfZion/neo-go/pkg/network.(*Server).Start(0xc0000ca000, 0xc000072ba0)
Feb 13 16:14:50 neo-go-node-2 neo-go[9448]: #11/go/src/github.com/CityOfZion/neo-go/pkg/network/server.go:173 +0x2ec
Feb 13 16:14:50 neo-go-node-2 neo-go[9448]: created by github.com/CityOfZion/neo-go/cli/server.startServer
Feb 13 16:14:50 neo-go-node-2 neo-go[9448]: #11/go/src/github.com/CityOfZion/neo-go/cli/server/server.go:331 +0x476
...
Feb 13 16:14:50 neo-go-node-2 neo-go[9448]: goroutine 2199 [chan send, 870 minutes]:
Feb 13 16:14:50 neo-go-node-2 neo-go[9448]: github.com/CityOfZion/neo-go/pkg/network.(*TCPPeer).Disconnect.func1()
Feb 13 16:14:50 neo-go-node-2 neo-go[9448]: #11/go/src/github.com/CityOfZion/neo-go/pkg/network/tcp_peer.go:366 +0x85
Feb 13 16:14:50 neo-go-node-2 neo-go[9448]: sync.(*Once).Do(0xc030ab403c, 0xc02f262788)
Feb 13 16:14:50 neo-go-node-2 neo-go[9448]: #11/usr/local/go/src/sync/once.go:44 +0xb3
Feb 13 16:14:50 neo-go-node-2 neo-go[9448]: github.com/CityOfZion/neo-go/pkg/network.(*TCPPeer).Disconnect(0xc030ab4000, 0xd92440, 0xc000065a00)
Feb 13 16:14:50 neo-go-node-2 neo-go[9448]: #11/go/src/github.com/CityOfZion/neo-go/pkg/network/tcp_peer.go:365 +0x6d
Feb 13 16:14:50 neo-go-node-2 neo-go[9448]: github.com/CityOfZion/neo-go/pkg/network.(*TCPPeer).SendPing.func1()
Feb 13 16:14:50 neo-go-node-2 neo-go[9448]: #11/go/src/github.com/CityOfZion/neo-go/pkg/network/tcp_peer.go:394 +0x42
Feb 13 16:14:50 neo-go-node-2 neo-go[9448]: created by time.goFunc
Feb 13 16:14:50 neo-go-node-2 neo-go[9448]: #11/usr/local/go/src/time/sleep.go:169 +0x44
...
Feb 13 16:14:50 neo-go-node-2 neo-go[9448]: goroutine 3448 [chan send, 854 minutes]:
Feb 13 16:14:50 neo-go-node-2 neo-go[9448]: github.com/CityOfZion/neo-go/pkg/network.(*TCPPeer).handleConn(0xc01ed203f0)
Feb 13 16:14:50 neo-go-node-2 neo-go[9448]: #11/go/src/github.com/CityOfZion/neo-go/pkg/network/tcp_peer.go:143 +0x6c
Feb 13 16:14:50 neo-go-node-2 neo-go[9448]: created by github.com/CityOfZion/neo-go/pkg/network.(*TCPTransport).Accept
Feb 13 16:14:50 neo-go-node-2 neo-go[9448]: #11/go/src/github.com/CityOfZion/neo-go/pkg/network/tcp_transport.go:62 +0x44c
...

The problem is that the select in putPacketIntoQueue() only works the way it
was intended to after the close(p.done), but that happens only after
successful unregistration request send. Thus, do disconnects the other way
around, first unblock queueing and exit goroutines, then destroy the
connection (if it wasn't previously destroyed) and only after that signal to
the Server.

Problem

...

Solution

...

[codecov]

Codecov Report

Merging #663 into master will not change coverage by %.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #663   +/-   ##
=======================================
  Coverage   64.84%   64.84%           
=======================================
  Files         125      125           
  Lines       10607    10607           
=======================================
  Hits         6878     6878           
  Misses       3450     3450           
  Partials      279      279           

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[roman-khimov]

This lock subsequently leads to socket leakage, which in turn leads to the node yelling at the log:

Feb 13 15:29:21 neo-go-node-2 neo-go[9448]: 2020-02-13T15:29:21.265+0300        WARN        TCP accept error        {"error": "accept tcp [::]:10333: accept4: too many open files"}
Feb 13 15:29:21 neo-go-node-2 neo-go[9448]: 2020-02-13T15:29:21.266+0300        WARN        TCP accept error        {"error": "accept tcp [::]:10333: accept4: too many open files"}
Feb 13 15:29:21 neo-go-node-2 neo-go[9448]: 2020-02-13T15:29:21.267+0300        WARN        TCP accept error        {"error": "accept tcp [::]:10333: accept4: too many open files"}
Feb 13 15:29:21 neo-go-node-2 neo-go[9448]: 2020-02-13T15:29:21.268+0300        WARN        TCP accept error        {"error": "accept tcp [::]:10333: accept4: too many open files"}

which then quickly drains free disk space locking the system even further.