Hi Ned,
On 01/16/2017 09:11 PM, Ned Freed wrote:
Does :index still behave in the same way with the :count match-type that
it does with :value, :is, :regex, etc?
That depends on the context. :index is associated with multiple
extensions;
its meaning depends on which one you're talking about.
For example, the index extension only specifies how :index works with the
header, address, and date tests. Note that these are tests, not
actions, and
the interpretation of the combination of :index and :count is pretty
clear
given the "number of specified entities" language in RFC 5231 section
4.2:
:index restricts the test to Nth field, adding :count to that
basically then
gives you a 1 or 0 depending on whether or not there is an Nth field,
which is
what is tested. (And in the case of the date test, it's further
restricted to
fields containing valid dates.)
In other words, these two tests are basically equivalent:
header :index 4 :count "gt" :comparator "i;ascii-numeric" "foo" "0"
header :index 4 :matches "foo" "*"
Personally, I think the second test is much clearer, but YMMV.
The :index that's part of deleteheader action isn't part of the index
extension, but works pretty much the same way: It restricts the entire
operation to the Nth field. And in this case the specification is very
clear
(secion 5, fourth paragraph) that the <value-patterns> check, which would
necessarily include :count, happens *after* the :index restriction is
applied.
And this means that
deleteheader :index 2 :count "ge" :comparator "i;ascii-numeric"
"X-foo" [ "3" ]
is a no-op, because the :index restriction is applied first, and means
that the
number of fields under consideration is either 0 or 1, and can be >=3.
And that
makes the addition of :count to :index useless in this context.
But more generally, the :count match type really only makes sense in the
context of tests or actions on at most one thing. It sort of falls
apart in the
context of action that's acting on multiple things, because it makes
sense to
apply the test part of an action on a case by case basis to the set of
things the action is being applied to, and use that result to control
whether
or not to apply the action.
But the semantics of :count are "count the number of things and then test
that". And while that plays fairly nicely with tests, it's really at odds
with action semantics.
More generally still, since :count is wierd, the accepted convention
is for new
actions and tests to specify how :count works for them. RFC 5260 does
this for
both currentdate and date. RFC 5703 explains how :count and :mime
interact. And
so on.
But editheader didn't do that for deleteheader, and that IMO means the
behavior
of :count in the context of deleteheader is undefined unless :index is
also
present, in which case it's useless.
I also don't think that saying that :count tests perform a preliminary
count
like :index :last is especially useful - can you think of a case where
you'd
want to delete all headers of a given type based on how many of them are
present? I can't.
No I can't, which is why I started thinking about the semantics of
:count with deleteheader. I'm fine making it a no-op or a syntax error.
--
Kenneth Murchison
Principal Systems Software Engineer
Carnegie Mellon University
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