dns.setServers() crash

[BLeQuerrec]

Hi,

In a Vagrant Ubuntu environment, io.js crashes with this code:

$ cat dns.js
var dns = require('dns');

dns.resolveSoa('example.org', function(err, soa){
    console.log(soa.nsname);
    dns.resolve4(soa.nsname, function (err, nameServers) {
        console.log(dns.getServers());
        dns.setServers(nameServers);
        console.log(dns.getServers());
    });
});

Expected result:

$ iojs dns.js
sns.dns.icann.org
[ '10.0.2.3' ]
[ '199.4.28.26' ]

Actual result:

$ iojs dns.js
sns.dns.icann.org
[ '10.0.2.3' ]
iojs: ../deps/cares/src/ares_destroy.c:102: ares__destroy_servers_state: Assertion `ares__is_list_empty(&server->queries_to_server)' failed.
Aborted (core dumped)

Other informations:

$ cat /etc/os-release
NAME="Ubuntu"
VERSION="14.04.1 LTS, Trusty Tahr"
ID=ubuntu
ID_LIKE=debian
PRETTY_NAME="Ubuntu 14.04.1 LTS"
VERSION_ID="14.04"
HOME_URL="http://www.ubuntu.com/"
SUPPORT_URL="http://help.ubuntu.com/"
BUG_REPORT_URL="http://bugs.launchpad.net/ubuntu/"
$ iojs -v
v1.2.0

DNS test (in test/simple/test-dns.js) ends successfully. This bug can be fixed by removing line 102 in deps/cares/src/ares_destroy.c.
Node.js bug: nodejs/node-v0.x-archive#9243

[tellnes]

I'm seeing similar results on os x 10.9.5

$ iojs dns.js
sns.dns.icann.org
[ '10.0.0.1' ]
Assertion failed: (ares__is_list_empty(&server->queries_to_server)), function ares__destroy_servers_state, file ../deps/cares/src/ares_destroy.c, line 102.
Abort trap: 6

[rvagg]

@iojs/tc can someone qualified jump on this? otherwise it'll have to go in to "known issues" in 1.3.0.

[indutny]

Will do.

[indutny]

I have two solutions to the problem:

• cares: fix set_servers during active queries #899
• throw in JS if there is any active queries
• wait until query completion before changing the servers

What do you think will be most preferable? cc @bnoordhuis

[silverwind]

wait until query completion before changing the servers

Would that block new queries from using the updated servers until all outstanding requests finish? If so, any way to have setServers apply for all following queries?

[tellnes]

The best solution would be that queries created before calling setServers is using the old servers while queries created after calling setServers is using the new servers.

If I understand your solutions correctly, that would mean wait until query completion and queue up new queries.

[silverwind]

Meant what @tellnes said. If that's possible, there's no need to throw.

[indutny]

Good suggestion. I'll see what I can do.

[silverwind]

I'm unsure how far you got here @indutny, but if it proves easier to add support for a server option on resolve like I proposed in #1071, we could possibly deprecate setServers and getServers in 2.0 or 3.0.

[silverwind]

Once this is fixed to work like #894 (comment) describes, I can work on adding the resolve option for a truly async API. Probably not worth to deprecate after all.

[silverwind]

@emotional-engineering c-ares is now on GitHub. Would you mind posting your patch as a pull request there? @indutny mentioned they should be more responsive now.

[silverwind]

Filed c-ares/c-ares#41

[jasnell]

Closing this as it's a duplicate of #1071 (or, 1071 is a duplicate of this... either way, we don't need two issues tracking the same problem). It's still an open issue, however.

[silverwind]

I have to object. This is the original issue tracking the crash. The other one is more of an API topic.

@indutny you're still assigned here?

[jasnell]

@silverwind .. ok, no problem :-) just trying to do a bit of housecleaning.

[raimondi1337]

Ran into this issue today on node v6.9.1

I'm running this loop thousands of times one after another and it works:

    dns.setServers([server['ip']]);
    dns.lookup('something.com', fn()(...));

but this breaks after two executions resulting in the error in the original post:

    dns.setServers([server['ip']]);
    dns.resolve('something.com', fn()(...));

has this been fixed for lookup but not resolve or something like that?

[silverwind]

@raimondi1337 lookup uses the system resolver, so does not go through c-ares. setServers has no effect on lookup.

[dzek69]

If noone noticed - this is fixed with 9.3.0 version and fix seems to be backported to 8.10.0 too.

But I monkey patched dns module to fix that - if anyone needs to keep unpatched Node version and doesn't want the crashes - please use my fix.
More information here: https://github.com/dzek69/node-dns-bugfix