Add 'slave_repl_offset' to the INFO replication command output

[Kilowhisky]

This adds support for slave_repl_offset to the INFO REPLICATION command.

I just grabbed the int(s.faofsz) from here (output of the ROLE command). Can you confirm this would be the right stat to grab? I don't really see where this gets updated. I guess i could have just used the s.aofsz which does get updated...

For my purposes, i guess as long as its not 0 it should fix my problem.

tile38/internal/server/stats.go

Lines 633 to 639 in a953466

	} else {
	role = "slave"
	host = s.config.followHost()
	port = s.config.followPort()
	offset = int(s.faofsz)
	state = "connected"
	}

This fixes #750

[shakefu]

@tidwall Any chance we can get this reviewed for upstream acceptance?

[iwpnd]

@tidwall Any chance we can get this reviewed for upstream acceptance?

🥴

[Kilowhisky]

I just tested this PR against an active master as a new follower and it behaved as expected. So it looks like i got the right property.

info replication
# Replication
role:slave
master_host:10.134.72.107
master_port:9851
slave_repl_offset:1352875844
connected_slaves:0

info replication
# Replication
role:slave
master_host:10.134.72.107
master_port:9851
slave_repl_offset:1374752031
connected_slaves:0

output JSON
{"ok":true,"elapsed":"1.31  s"}

info replication
{"ok":true,"info":{"connected_slaves":0,"master_host":"10.134.72.107","master_port":9851,"role":"slave","slave_repl_offset":1297572539},"elapsed":"44.621  s"}

As seen above, the offset is increasing as expected.

[tidwall]

LGTM.