facter -p returns NUL character on stdout when called from nested ruby on windows

As result of the investigation into MODULES-10602 and FM-8887, it was found that facter misbehaves on windows when being called from another ruby process while at the same time also executing other processes:

When deploying the following fact to C:\ProgramData\PuppetLabs\puppet\cache\lib\facter\debugg.rb

Facter.add(:debugg) do

  setcode do

    puts `cmd /c echo bar`.inspect

  end

end

weird things start to happen:

PS C:\> & 'C:\Program Files\Puppet Labs\Puppet\puppet\bin\irb.bat'

irb(main):001:0>  `facter -p debugg`

=> "\x00\"bar\\n\"\n"

irb(main):002:0>

Note the \x00 at the start of the output. Replacing the backtick-call to cmd in the fact with a regular string makes the behaviour go away:

Facter.add(:debugg) do

  setcode do

    puts "bar\n".inspect

  end

end

irb(main):002:0> `facter -p debugg`

=> "\n\"bar\\n\"\n"

irb(main):003:0>

Curiously, using Puppet::Util::Execution.execute for calling facter also does not show the issue:

irb(main):004:0> Puppet::Util::Execution.execute("facter -p debugg")

=> "\n\"bar\\n\"\n"

irb(main):005:0>

I could verify that this is the cause for the behaviour seen in MODULES-10602 and FM-8887, and I could reproduce it with only the latest puppet-agent (6.16.0) installed on a windows server 2019 virtual box (gusztavvargadr/windows-server). Customers and SEs have reported seeing the same symptoms as far back as 2019.2.1.

For a full-featured repro environment, the hydra demo environments work out of the box, as (amongst others) the chocolateyversion fact triggers the bug.

I could not reproduce it on a litmusimage/centos:8 docker image with the same agent version:

david@zion:~/git/puppetlabs-motd (master)$ docker exec -ti litmusimage_centos_8-2225 /bin/bash

[root@40541a36d2a8 /]# cat /opt/puppetlabs/puppet/cache/lib/facter/debugg.rb

Facter.add(:debugg) do

  setcode do

    #puts `cmd /c echo bar`.inspect

    puts `echo bar`.inspect

  end

end

[root@40541a36d2a8 /]# /opt/puppetlabs/puppet/bin/irb 

irb(main):001:0> `facter -p debugg`

=> "\n\"bar\\n\"\n"

irb(main):002:0> exit

[root@40541a36d2a8 /]# puppet --version

6.16.0

[root@40541a36d2a8 /]# 

https://github.com/puppetlabs/puppetlabs-facter_task/pull/125 has a workaround for the facter_task task. Since it is neither a straight up functional equivalent, nor keeps other tasks from breaking, I'm hesitant to commit that PR as a "fix" for this issue.

See https://puppet.slack.com/archives/CF418R4BE/p1592905228073600 for extensive just-in-time debugging log.