F.Zappa - excerpt from "The Torture Never Stops":
"Flies all green and buzzin'
In the dungeon of despair
Who are all those people
That he's locked away down there
Are they crazy
Are they sainted
Are they zeros someone painted
That had never been explained
Since at first it was created
But a dungeon like a sin
Requires not much lockin' in
Of everything thats ever been"
(http://www.metrolyrics.com/the-torture-never-stops-lyrics-frank-zappa.html
for full lyric)
Somehow fitting, Halloween and all... for what I want to bring up.
Yet again someone was bit by the automatic String to Numeric conversion
that is in Puppet (and also in --parser future).
The particular thing this time was
https://tickets.puppetlabs.com/browse/PUP-3602 that caused certain md5
fingerprints to look like floating point values of value 0 (they all
started with "0e" but had different digits after the e, and since 0 * 10
^something is always 0 the two different md5 fingerprints were reported
to being equal.
This is not the only place where String to number conversion is a very
bad idea. Someone recently had problems with conversions in a case
where string comparison was wanted for version strings.
https://tickets.puppetlabs.com/browse/PUP-3333 has the details.
With --parser future it is at least consistent. In 3x different
operators used different rules. Now <, >, <=, >=, ==, and != all share
the same behavior; they convert a string to numeric if both sides of the
expression are numeric or can be converted to numeric.
The in operator has some additional rules (see the spec, but it uses
the same comparisons as for the regular operators).
We fixed PUP-3602 by not converting strings that are floating point 0
with exponential part and we also do not convert values that are
floating point infinite in Ruby (e.g. 4e999 and such). This is a crutch
though, and it is only a matter of time until someone stumbles over the
next SURPRISE !
The best cure is naturally to never do String to numeric conversion. And
we wonder what people feel about that. Should we go for this in Puppet
4.0.0 (and have a 3.7.4 release as the last of the 3x series where this
behavior is implemented when using --parser future).
There has also been a number of other suggestions how to fix this, that
are less appealing, and for the sake of not having to waste anyone's
time, here they are, with the reasons why they are not so appealing.
* Only convert if LHS is a Number. This makes the order of the
comparison matter and then ($x == $y) != ($y == $x) which is really bad.
* Add === operator to compare both type and value. This is a slippery
slope since we probably want Integer and Float to compare equal - say
0.0 and 0. It adds yet another operator, and we have to decide what
case, selector and in should use since there is no way to specify if one
or the other should be used.
Instead, since we already have sprintf for value to string conversion,
and there is a scanf in Ruby which does the conversion the other way, we
can simply add that function to core puppet for value conversion.
We could also add to_number(s), or to_number(s, format_string).
When doing that though, we risk ending up with a plethora of to_xxx
functions, and we could instead offer one more universal
convert_to(Type, value, options) function e.g.
# best effort, or fail
convert_to(Number, value)
# only if it is an integer, or fail
convert_to(Integer, value, {base => 10})
# convert integer to hex string with some extra text (the sprintf way)
convert_to(String, value, {format => "Hex %x"})
# convert to array of string (give full control over all
# nested conversions.
#
convert_to(Array[String], value, {
Integer => { format => "0x%x" },
Float => { format => "%#.4G" }})
# etc.
So - "Boldly break all the (s)t(r)hings"?
- henrik
--
Visit my Blog "Puppet on the Edge"
http://puppet-on-the-edge.blogspot.se/
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