0004175: sv_updatemaster uses synchronous gethostbyname

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Date Submitted

Last Update

0004175

Zandronum

[All Projects] Bug

public

2023-12-15 15:45

Reporter

tautvis

Assigned To

Priority

normal

Severity

minor

Reproducibility

always

Status

new

Resolution

open

Platform

Linux

OS Version

6.5

Product Version

3.1

Target Version

Fixed in Version

Summary

0004175: sv_updatemaster uses synchronous gethostbyname

Description

The the name `masterhostname` is resolved by directly calling gethostbyname function (in networkshared.cpp), which stall engine until dns resolution is done as it usually is up to few milliseconds time. But there are multiple cases when then time can be higher:
1) Using dns server which is not local, for example 8.8.8.8, 1.1.1.1 etc.., in my case for 8.8.8.8 request time is ~28ms, on 1.1.1.1 when cache is cold (all ttls expired) ~75ms!, but on hot case time <1ms
2) When DNS cache is cold and record ttl reached end of life (in master.zandronum.com is 300 seconds) - my local dns resolves ~28ms
3) dns packet is lost - stall ~2s (depends on system settings) + time for repeat request

On first glance does not look something worry as having multiple servers using same dns it would cause some very rare occasionally stutters. But if it is personal server with single zandronum instance it starts to be noticeable as persistent random stutters here and there when playing on local (i mean <10ms ping) network and if isp internet is down game starts to become unplayable (due to 2s timeout every 30seconds)

The quick remedy is to turn off master server update (set sv_updatemaster false).
Other remedies is set master server ip in /etc/hosts (or equivalent file) or use ip address in cvar instead hostname - but the price is to have periodically recheck if master server ip is changed as it defeats dns purpose...

for example dig report for 'unlucky' dns query for master.zandronum.com (it took 75msecs):

```
pc@pc ~ $ dig master.zandronum.com @1.1.1.1

; <<>> DiG 9.18.12 <<>> master.zandronum.com @1.1.1.1
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 53111
;; flags: qr rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 1

;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 1232
;; QUESTION SECTION:
;master.zandronum.com. IN A

;; ANSWER SECTION:
master.zandronum.com. 300 IN A 45.56.67.39

;; Query time: 75 msec
;; SERVER: 1.1.1.1#53(1.1.1.1) (UDP)
;; WHEN: Fri Dec xx xx:xx:xx EET 2023
;; MSG SIZE rcvd: 65

```

Steps To Reproduce

Start game with master server update on.

a) Set dns server to something 8.8.8.8 or 1.1.1.1 - anything with longer ping, it is very noticeable on cacos (they start teleporting here and there);
b) Set non-existing dns server - that worst case and permanent 2secs lags every 30seconds;
c) start game normally and use firewall (probably on router) to block dns ip address;

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Issue History
Date Modified	Username	Field	Change
2023-12-15 15:45	tautvis	New Issue

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