192798 - DNS: Offline->Online does not clear the DNS cache

Status: RESOLVED WORKSFORME

(Core :: Networking, defect, P2)

Description

[benc]

CONFIRMED: Mozilla 1.3a, Mac OS X

This behavior was added at some point, but I could not find a bug, so I'm
creating it now.

STEPS:
Using some DNS server logging (I used snoop), if you go to the same hostname
several times, you only see a DNS request for the first time.

If you click offline, then online, and go to the same hostname again, you find
that DNS is requested again, just once, for the hostname.

If anyone could put some comments about where and when this change was made,
that would be helpful.

Comment 1

[Darin Fisher]

benc:

this has been a feature of necko for as long as i have been working on it.  it
may have been broken at one point when the DNS service wasn't being shutdown as
a result of going offline.

no reason to keep this bug open.  marking WORKSFORME.

Comment 2

[benc]

VERIFIED:
just needed to document this somewhere, because I don't think I ever stumbled
across the bug that explained this was a feature.

Comment 3

[gordon]

This is currently broken.

Comment 4

[gordon]

I'll take it.

Comment 5

[benc]

*** Bug 196362 has been marked as a duplicate of this bug. ***

Comment 6

[Nicholas Allen]

*** Bug 200772 has been marked as a duplicate of this bug. ***

Comment 7

[timeless]

.

Comment 8

[timeless]

Attachment: draft

Comment 9

[gordon]

Timeless, this patch doesn't clear the DNS cache, and it would cause a
regression by potentially locking up the UI when we go offline.  This bug is
actually a regression from that one.

This would be fixed by the move to multiple lookup threads we've been
contemplating, but I think I know a simpler way to fix this in the meantime. 
I'll try to post a patch later today or tomorrow.

Comment 10

[timeless]

Attachment: clear cache

Comment 11

[Brendan Eich [:brendan]]

Comment on attachment 119942 [details] [diff] [review]
clear cache

>-    if (!nsCRT::strcmp(NS_XPCOM_SHUTDOWN_OBSERVER_ID, topic))
>+    if (!strcmp(NS_XPCOM_SHUTDOWN_OBSERVER_ID, topic))
>     {

Someone previously didn't follow prevailing brace style, here -- fix?

>         // we need to shutdown!
>         ShutdownInternal(); 
>         return NS_OK;
>     }
> 
>-    if (nsCRT::strcmp(NS_PREFBRANCH_PREFCHANGE_TOPIC_ID, topic))  
>+    NS_ConvertUCS2toUTF8 observerData(data);
>+    if (!strcmp("network:offline-status-changed", topic) &&
>+        !strcmp("online", observerData.get())) {
>+        // Force a reset

Don't construct observerData until you know you need it (after the first clause
of the && is known to be true) -- split that if condition across two ifs, with
the observerData declaration in the outer then block.

/be

Comment 12

[gordon]

Attachment: patch to clear dns cache after toggling offline/online

The DNS service already gets called when going offline, so we don't need any
observer code.	We simply set a flag in the Shutdown() to clear the dns cache
and reset the resolver the next time we get called to Lookup() or Resolve() a
hostname.

Comment 13

[gordon]

Comment on attachment 120267 [details] [diff] [review]
patch to clear dns cache after toggling offline/online

Darin, your thoughts and comments will be appreciated.	Any recommendations for
a reviewer?  Thanks.

Comment 14

[gordon]

Comment on attachment 120267 [details] [diff] [review]
patch to clear dns cache after toggling offline/online

Doug, can you review this as well?  Thanks.

Comment 15

[Darin Fisher]

Comment on attachment 120267 [details] [diff] [review]
patch to clear dns cache after toggling offline/online

>+        if (mCacheNeedsClearing) {
>+            EvictLookupsIfNecessary(0);     // clear cache
>+            Reset();                        // reset resolver
>+            mCacheNeedsClearing = PR_FALSE;
>+        }
>+
>         PLDHashEntryHdr * hashEntry = PL_DHashTableOperate(&mHashTable, i_hostname, PL_DHASH_LOOKUP);

no need to lookup in hash table if you just cleared the cache.	an
else clause is probably all that's needed.

sr=darin with that change.

Comment 16

[Doug Turner (:dougt)]

Comment on attachment 120267 [details] [diff] [review]
patch to clear dns cache after toggling offline/online

what darin said.

Comment 17

[Felix Miata]

*** Bug 202565 has been marked as a duplicate of this bug. ***

Comment 18

[gordon]

Patch checked in.  Marking FIXED.

Comment 19

[Felix Miata]

I guess now, if there isn't one already, we need a way to reload DNS/hosts
without going offline, which disconnects Chatzilla (remote closed the
connection) at offline without reconnecting at online.

Comment 20

[benc]

Felix: I've created bug 209729, based on your comment.

Comment 21

[benc]

REOPEN:
Mach-O, Mozilla 1.4b
WinXP, Mozilla 1.4 daily (20030612)

Maybe there is some OS-level caching that interfers w/ my test. 

I'm basically running a packet trace on the UDP port of the DNS server, and then
initiating browser activity that is not cached to the same hostname.

The cache is working: a single request for each host visited. However, after
clicking on the toggle button, only Linux begins to send out a new set of
queries for previously cached hostnames.

I've also noticed that for Linux, it does work, but not completely consistently
(90%) of the time. I also suspect that you have to double-click the toggle (go
offline and then go right back online).

Comment 22

[Samir Gehani]

adt: nsbeta1-

Comment 23

[Matthew Elvey]

WinXP:WorksForMe, Mozilla 1.5b.
benc: please reconfirm within a week, or I'll close it; otherwise I can reassign
it to the component owner.  I was able to flush an expired entry by selecting
"File..Work Offline" twice, for a website whose IP had changed.

Comment 24

[Scott Brawner]

Any idea as to how this will be handled in Firebird, as there is no
"online/Offline" button in the status bar and no "File > Work Offline" in the menu?

Comment 25

[benc]

Scott,

You should create a firebird bug that depends on this. I don't know what they
plan to do in this regard.

Comment 26

[Darin Fisher]

WORKSFORME