Re: DNSJava failing to lookup records?

[Brian W. <bwe...@xb...>]

On Mon, 20 Oct 2003, Andrew Houghton wrote:

> Here at VolunteerMatch we use dnsjava (1.3.3) to do some basic semantic 
> verification of user email addresses before they're added to our 
> system.  Users enter an email address for most important site actions, 
> and we do logical RFC 2822 checks followed by a simple test along the 
> lines of 'does this domain have an MX record? if not, does it have an A 
> record?'.
> 
> On Sunday, after restarting our servlet engine (Jetty 4.2.12 running on 
> RH Linux 7.3, Sun JDK 1.4.0), every record lookup was returning null.  
> This has happened once before on a brand new machine, and we chalked it 
> up to setup problems (we had some problems in our resolv.conf that 
> needed fixing).  This time around, though, there weren't any changes in 
> the system to cause the problem.  For the record, using dig to lookup 
> records from a shell worked fine for the same domains that dnsjava was 
> failing on.

What does Lookup.getErrorString() return for the failed queries?

> My first guess was that dnsjava simply had some problems reading or 
> parsing resolv.conf, and thus the initialization step was booched, but 
> that doesn't make much sense to me given that on any normal day it 
> doesn't have this problem.  I'm about to dive into the code to try and 
> figure out what's going on, but can anyone offhand give any ideas?  Has 
> anyone seen this problem?

I've never heard of any problems with the resolv.conf parser, but it's 
possible.

> And, most importantly, is there a way to force dnsjava to initialize and 
> return some sort if a status code?  I'm not certain what a status code 
> would mean in this case, but ideally I'm looking for some way of finding 
> what dnsjava is using as name servers, how it decided on them, and 
> whether the initialization process had any problems.

Setting the verbose option (-Ddnsjava.options=verbose) will cause the 
resolv.conf parser, called from the initialization code, to print a 
message for each server it parses (in the FindServer.addServer() method).  
There's also the FindServer.servers() static method, which returns the 
servers being used (or the FindServer.searchPath() method returning the 
domain search list).  Setting the verbose option will also cause each 
lookup to log a message, so while useful for debugging, it's probably not 
something you'd want on all the time.

I'm not sure how much this helps, but it should tell you if there's a 
problem with initialization or something later.

Brian