[OpenSIPS-Devel] ENUM lookups, q-value, and serialize_branches()

[Phil Vandry]

Hello,

I noticed that when the enum_query() function received more than one
result from DNS, it appends branches and sets the q-value for each
branch based on the order and preference values from the DNS result.
But I do not think that the way it does this is correct.

EXISTING BEHAVIOUR:

Basically, it does the equivalent of sorting the records first by order
and then by preference, and assigning q-values in decreasing order with
DNS records having identical order&preference receiving identical q.

If you combine enum_query() with serialize_branches(), the effect is
that the DNS results are tried in order of order&preference and results
with identical order&preference use parallel forking.

CORRECT BEHAVIOUR (RFC 2915):

The DNS results must be considered in order of NAPTR "order". Once a
result is found whose rule "matches" the target, the client MUST NOT
consider any NAPTRs with a higher value for order. In order words,
once we find a record of the correct form with the service we want and
the flags we expect, all lesser-order records are discarded, *not*
added as later branches.

Next, for records with identical preference, the records must be chosen
in round-robin fashion (load balancing between them). ENUM does not
provide any mechanism for parallel forking.

I have a patch that changes the behaviour of the enum module to be
compliant to the standard but obviously it will break any script that
relies on the current behaviour. What solution would you suggest? Does
anybody depend on the current behaviour?

-Phil