I was re-reading the libravatar specification today, and noticed that I
had missed a section that described what to do if a DNS query results in
multiple records. The current implementation just used a "simple"
(dns-query ...) but that is explicit not sufficient. Instead one must
choose the highest priority servers and then randomly select one of
these, according to their weights. The patch I have attached to this
mail implements this, and can be tested by evaluating

	(gravatar--service-libravatar "test@pusling.com")

It's rather hard to find a domain with multiple libravatar entries, but
the selection algorithm can be tested using this slightly modified
excerpt from the patch:

    (defun test-selection ()
      (catch 'found
        ;; res is a hardcoded and simplified (dns-query "..." t) result.
        ;; "target" would usually point to a domain.
        (let* ((res '(((target alpha) (priority 10) (weight 10))
                      ((target beta) (priority 10) (weight 0))
                      ((target gamma) (priority 10) (weight 30))
                      ((target delta) (priority 5) (weight 10))))
               (prio (mapcar (lambda (r) (dns-get 'priority r)) res))
               (max (apply #'max prio))
               (sum 0) top)
          (dolist (rec res)
            (when (= max (dns-get 'priority rec))
              (setq sum (+ sum (dns-get 'weight rec)))
              (push rec top)))
          (dolist (rec top)
            (when (<= (if (= 0 sum) -1 (random sum))
                      (dns-get 'weight rec))
              (throw 'found (dns-get 'target rec)))
            (setq sum (- sum (dns-get 'weight rec)))))))

    (/ (cl-loop repeat 1000 count (eq (test-selection) 'gamma)) 1000.0)

where the last expression should approximately equal 0.75 (3/4), because
only the records alpha, beta and gamma have the highest priority (10),
and between them gamma has a 30/(10 + 30) = 3/4'th chance of being
chosen. In case all records are weighted 0, the first one is chosen.

I once again apologise for not thoroughly enough testing my last patch,
and hope this at least somewhat makes up for it.

-- 
	Philip K.