How do you know what variables are frozen?

[Trevor Vaughan]

I *think* I've just run into a case where I was trying to run strip! on a frozen Facter variable.

1) How do we know what variables are frozen coming from Facter?

2) What is the best way to ensure that our tests check for this case?

Thanks,

Trevor

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[Peter Huene]

On Wed, Jul 15, 2015 at 8:59 AM, Trevor Vaughan <tvau...@onyxpoint.com> wrote:

I *think* I've just run into a case where I was trying to run strip! on a frozen Facter variable.

1) How do we know what variables are frozen coming from Facter?

Facter shouldn't be freezing resolved fact values, so is this something that a custom fact is explicitly doing to the returned value?

http://ruby-doc.org/core-2.2.2/Object.html#method-i-frozen-3F should work for checking in an object is frozen, though.

 

2) What is the best way to ensure that our tests check for this case?

Thanks,

Trevor

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[R.I.Pienaar]

----- Original Message -----
> From: "Peter Huene" <peter...@puppetlabs.com>
> To: "puppet-dev" <puppe...@googlegroups.com>
> Sent: Wednesday, July 15, 2015 5:18:29 PM
> Subject: Re: [Puppet-dev] How do you know what variables are frozen?

> On Wed, Jul 15, 2015 at 8:59 AM, Trevor Vaughan <tvau...@onyxpoint.com>
> wrote:
>
>> I *think* I've just run into a case where I was trying to run strip! on a
>> frozen Facter variable.
>>
>> 1) How do we know what variables are frozen coming from Facter?
>>
>
> Facter shouldn't be freezing resolved fact values, so is this something
> that a custom fact is explicitly doing to the returned value?
>
> http://ruby-doc.org/core-2.2.2/Object.html#method-i-frozen-3F should work
> for checking in an object is frozen, though.
>

but surely you should just assume you cant change variables especially facts?
since that's their intended use, no modifying of variables?

Be interesting to hear why a fact is being tripped in a destructive way :)

[Trevor Vaughan]

In this case, it was a custom function that was tripping things up.

Looking through the code, I *think* this was the scenario:

1) Fact => trusted['certname']

2) Function call to parse_host($trusted['certname'])

3) Parse host:

host = args.first

host.strip! # Here's the offender

I also tried seeing if dup'ing the args would work, but it copies the frozen attribute with the String object (which makes sense).

So, I don't know if I was trying to modify something from a Fact or if the object just happened to be carrying the 'frozen' status as it went along.

Thanks,

Trevor

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[R.I.Pienaar]

----- Original Message -----
> From: "Trevor Vaughan" <tvau...@onyxpoint.com>
> To: "puppet-dev" <puppe...@googlegroups.com>
> Sent: Wednesday, July 15, 2015 7:50:36 PM
> Subject: Re: [Puppet-dev] How do you know what variables are frozen?

> In this case, it was a custom function that was tripping things up.
>
> Looking through the code, I *think* this was the scenario:
>
> 1) Fact => trusted['certname']
> 2) Function call to parse_host($trusted['certname'])
> 3) Parse host:
>
> host = args.first
> host.strip! # Here's the offender
>
> I also tried seeing if dup'ing the args would work, but it copies the
> frozen attribute with the String object (which makes sense).
>
> So, I don't know if I was trying to modify something from a Fact or if the
> object just happened to be carrying the 'frozen' status as it went along.

so do not use strip! use x = something.strip? this way you dont try to
modify anything in scope.

[Trevor Vaughan]

Indeed, I did change it to that but it would still be nice to know what's going on so that I can stuff it into rspec and check for it.

Thanks,

Trevor

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[Peter Huene]

On Wed, Jul 15, 2015 at 12:18 PM, Trevor Vaughan <tvau...@onyxpoint.com> wrote:

Indeed, I did change it to that but it would still be nice to know what's going on so that I can stuff it into rspec and check for it.

Puppet's compiler intentionally freezes $trusted and its values.  If you intend to support operating on arguments like this, you should be creating a copy and not modifying the argument (probably a good rule to follow anyway, especially for a function named "parse").

 

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[Trevor Vaughan]

Fair enough, and we usually do that. I just wanted to know what was frozen so that we could properly duplicate it in our spec tests.

Out of curiosity, why not freeze all strings from Facter?

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[Adrien Thebo]

It looks like we do: https://github.com/puppetlabs/puppet/blob/master/lib/puppet/parser/scope.rb#L652-L654

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[Adrien Thebo]

And it looks like _I_ was too hasty; this is done when immutable_node_data is set. (https://github.com/puppetlabs/puppet/commit/8ccb3923b7ddd22e53d53dd193edc618b218a2a6)

[Trevor Vaughan]

Ah, we use trusted_node_data so that's probably why I'm hitting this (and glad that I am so we caught that bug prior to release).

Why wouldn't this be the default?

Thanks,

Trevor

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[Adrien Thebo]

This not only became the default, but was removed as a tunable in Puppet 4: (https://github.com/puppetlabs/puppet/commit/19f223f2e2b20b19701472babfa66b0ceea59bae)

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[Trevor Vaughan]

Move along, nothing to see here.....

Thanks Adrien.

Trevor

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[Henrik Lindberg]

On 2015-15-07 12:22, Peter Huene wrote:
> On Wed, Jul 15, 2015 at 12:18 PM, Trevor Vaughan <tvau...@onyxpoint.com
> <mailto:tvau...@onyxpoint.com>> wrote:
>
> Indeed, I did change it to that but it would still be nice to know
> what's going on so that I can stuff it into rspec and check for it.
>
>
> Puppet's compiler intentionally freezes $trusted and its values. If you
> intend to support operating on arguments like this, you should be
> creating a copy and not modifying the argument (probably a good rule to
> follow anyway, especially for a function named "parse").
>

Peter is right. Rule of thumb, never ever mutate arguments that are
given to you or that you lookup. Unfortunately deep freezing all values
has a high cost or we would do that extensively when the puppet runtime
returns values, or calls into user supplied logic.

Regards
- henrik

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>
>
>
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> Trevor Vaughan
> Vice President, Onyx Point, Inc

> (410) 541-6699 <tel:%28410%29%20541-6699>

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