net: SocketHandler logs peer id for close and disconnect

[Sjors]

When combined with -logips this makes it easier to diagnose disconnects.

To test on macOS, find a connection you want to disrupt:

lsof -nP -iTCP:8333 -sTCP:ESTABLISHED

To shut it down gracefully you can use tcpkill or this Python script: https://github.com/google/tcp_killer

The log should say:

2019-10-25T13:26:55Z socket closed for peer=1
2019-10-25T13:26:55Z disconnecting peer=1
2019-10-25T13:26:55Z Cleared nodestate for peer=1

To shut it down ungracefully I made a patch to the above script, adding a -force argument. Careful, this may result in data corruption. Then the log should say:

2019-10-25T13:39:57Z socket select error Bad file descriptor (9)
2019-10-25T13:39:57Z socket recv error for peer=0: Bad file descriptor (9)
2019-10-25T13:39:57Z disconnecting peer=0
2019-10-25T13:39:57Z Socket close failed: 35. Error: Bad file descriptor (9)
2019-10-25T13:39:57Z Cleared nodestate for peer=0

[laanwj]

ACK b62013c

[maflcko]

This is already printed in the very next line

[Sjors]

@MarcoFalke true. It's not very grep-friendly though, and many other log messages do include peer=N. And I also mistook the error code for the node id.

[emilengler]

Don't know if it's a thing but why isn't the IP being displayed as well?

[Sjors]

@emilengler putting IP addresses in the log was disabled by default in #3764 for privacy reasons

[Sjors]

@TheBlueMatt suggested making the error message debug=net only

[maflcko]

unsigned ACK 04dbdd6

[TheBlueMatt]

unsigned ACK 04dbdd6 LGTM!

[theuni]

I've definitely hacked this in locally before.

unsigned ACK 04dbdd6.