From: Sam Roberts <sroberts@...>
Date: 2005-02-05T00:08:13+09:00
Subject: Re: 'example.com' == 'example.com.' => false... is this intended?

Quoteing akr@m17n.org, on Fri, Feb 04, 2005 at 05:02:45PM +0900:
> In article <20050204052951.GA2531@ensemble.local>,
>   Sam Roberts <sroberts@uniserve.com> writes:
> 
> > Why? When are they not the same?
> 
> For example, if you have a machine named "museum", it is confusing with
> "museum." domain.
> 
> > They are equivalent in the DNS, Resolv::DNS#getaddress() would return
> > the same A record for both.
> 
> There are several top-domains which have A record: ac, museum, etc.
> If your local domain have a machine named "ac", it is important to
> distinguish a relative "ac" domain and the absolute "ac" domain.

You only sometimes distinguish between the two, sometimes you convert
them to each other:

   >> Name = Resolv::DNS::Name
   => Resolv::DNS::Name
   >> Name.create('museum') == Name.create('museum')
   => true
   # But, wouldn't this depend on the location? On my net, museum would
   # be museum.local.
   >> Name.create('museum') == Name.create('museum.')
   => false
   >> Name.create('museum').to_s == Name.create('museum.').to_s
   => true
   # Isn't it important to distinguish?

   n0=Resolv::DNS.new.getname("193.108.154.9")

   n1=Resolv.getname("193.108.154.9")
     => "a193-108-154-9.deploy.akamaitechnologies.com"
   # note it isn't absolute, though the DNS response was

   n0 == n1
    => in `==': undefined method `absolute?' for "com":String (NoMethodError)
   # I have to change my String to a Name to compare it? Irritating.

   n1 = Resolv::DNS::Name.create(n0)
   n0 == n1
    => false
   # DNS returns absolute names
   n2 = Resolv::DNS::Name.create(n0.to_s)
   n0 == n2
    => false
   n0.to_s == n2.to_s
    => true

Maybe you haven't seen how unuseful the behaviour of == is because you
use it inside resolv.rb, and all names you see are absolute?

Outside of resolv.rb (including input/output values of the common Resolv
class methods) names are non-absolute strings, and the DNS Name objects
can't be compared to them.

> > Name doesn't have any comparison operators, so they occupy empty space.
> >
> > Do you have another idea on what Name < Name could mean?
> 
> For example, lexical order.
> 
> > I found it necessary to find whether a Name was a sub-domain of another.
> > How would you recommend to do this, if there is no method?
> >
> >   lhs.length > rhs.length && lhs.to_a[-rhs.length, rhs.length] == rhs.to_a
> >
> > is the best I came up with, and its not the kind of thing I would want
> > to type regularly.
> 
> Adding some method (not operator) is acceptable if it has a good name.

The code I posted included the method #lt?, you could include it as is,
or change its name. For consistency with #eql?, you may want to make it
NOT convert its argument from String to Name, or you may want to change
both to allow comparison to String.

def lt?(name)
  n = Name.create(name) # maybe remove?
  length > n.length && to_a[-n.length, n.length] == n.to_a
end

def ==(other)
  other = Name.create(other) # maybe add?
  return @labels == other.to_a && @absolute == other.absolute?
end
alias eql? ==


Cheers,
Sam