New feature in v3: cast!

Alan DeKok aland at
Sun May 12 14:49:07 CEST 2013

Brian Candler wrote:
> Hmm, I think this syntax is obscure.  Here the == operator is being changed
> to mean "is this IP address contained within that prefix"?  They're not
> equal to each other.  Perhaps something like =~ would be clearer?

  =~ already has a meaning as a regex operator.  So I'd like to avoid
using that.

> I'm also not sure that casting the LHS to <cidr> is a clear way of achieving
> this.  The LHS is, and remains, a single IP address.  The RHS is a CIDR
> prefix.

  The issue is that the code does type-specific comparisons.  It's hard
to know what's right for inter-type comparisons.

	if ( < 2)


> So I'd rather see:
> if (Framed-IP-Address =~ <cidr> { ... }

  That could work (maybe) with some changes.

> since the unquoted RHS literal can be unambiguously parsed as a CIDR prefix
> anyway,

  Well... maybe.  What about:

	if (Framed-IP-Address =~ "%{sql: ...") {

  Is the RHS a regex?  A CIDR comparison?  An IP address comparison?

  I'm trying to say that the code needs *unambiguous* rules.  Ad-hoc
rules work in some cases, and don't work in others.  So they can't be used.

  The casting, however, is always unambiguous.  Cast both sides to a
type, and do type-specific comparions.

> and a comparison of IP value with CIDR value have the obvious
> semantics.

  "obvious"?  What happens when an IP address is smaller than the CIDR
range?  Or greater than it?

  For CIDRs, we need at least a "contains" operator.  As in "does CIDR 1
contain CIDR 2".

> Maybe the reason for casting the LHS to <cidr> so that you can go a general
> comparison of (CIDR) to (CIDR) rather than (IP) within (CIDR).  In that
> case, the rules for comparing two (CIDR) values need to be clear.

  See Wikipedia for "range comparison" (IIRC).  There are 20+ types of
possible relationships for two ranges.  In contrast, integers just have
3 (and their negations).  ==, <, >  (and !=, >=, <=)

  It's much easier to just say define a "contains" operator for CIDRs.
That way you can't even *express* the other types of relationships.
Because they're not needed 99.999% of the time.  And if they are needed,
use Perl.

> Finally, there is a problem of what to do with modules like rlm_sql and
> rlm_files.  These are already restricted to returning LHS=attribute name,
> RHS=string literal.  Unfortunately we can't use the =~ operator here because
> people may already be doing things like
>     ("Framed-IP-Address", "=~", "^192\.168\.")
> So maybe it makes sense for these to return
>     ("<cidr>Framed-IP-Address", "=~", "")
> but this still doesn't feel quite right to me.

  That will probably *not* happen.

> Aside: if this is going to be done, I have a much more pressing need for
> being able to qualify the attribute with the list name:
>     ("reply:Framed-IP-Address", "=*", "present")
> At the moment I have to copy a bunch of attributes from the reply list to
> the request list, just so that rlm_sql can match them.

  Adding a list qualifier is probably easy.  It's on the "to do" items
for v3.

  Alan DeKok.

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