Fix read_tar_magic to properly return an array when a file has less than 264 characters

[bdwyertech]

Description

In the case that a file is smaller than 264 characters, nil is returned rather than an array, alas the pack method is not available.

This is what is causing the AppVeyor build failure on ChefDK.

undefined method `pack' for nil:NilClass

Issues Resolved

Hopefully this allows us to bump mixlib-archive to address chef-boneyard/chef-dk#1663 via chef-boneyard/chef-dk#1664

Check List

• New functionality includes tests
• All tests pass
• All commits have been signed-off for the Developer Certificate of Origin. See https://github.com/chef/chef/blob/master/CONTRIBUTING.md#developer-certification-of-origin-dco

[bdwyertech]

With mixlib-archive 0.4.13

Failing

require 'mixlib/archive'

def tempdir
  @tmpdir ||= Dir.mktmpdir("chef-dk")
  File.realpath(@tmpdir)
end

working_dir = ::File.join(tempdir, 'policyfile_services_test_working_dir')

archive_file_path = ::File.join('example-policy-abc123.tgz')

Zlib::GzipWriter.open(archive_file_path) do |gz_file|
  gz_file << "lol this isn't a tar file"
end


def read_tar_magic(io)
  io.rewind
  magic = io.read(512).bytes[257..264].pack("C*")
  io.rewind
  magic
end

def is_tar_archive?(io)
   !(read_tar_magic(io) =~ /ustar\s{0,2}\x00/).nil?
end


raw = ::File.open(archive_file_path, 'rb')

is_tar_archive?(raw)

Passing (Cast as Array)

require 'mixlib/archive'

def tempdir
  @tmpdir ||= Dir.mktmpdir("chef-dk")
  File.realpath(@tmpdir)
end

working_dir = ::File.join(tempdir, 'policyfile_services_test_working_dir')

archive_file_path = ::File.join('example-policy-abc123.tgz')

Zlib::GzipWriter.open(archive_file_path) do |gz_file|
  gz_file << "lol this isn't a tar file"
end


def read_tar_magic(io)
  io.rewind
  magic = Array(io.read(512).bytes[257..264]).pack("C*")
  io.rewind
  magic
end

def is_tar_archive?(io)
   !(read_tar_magic(io) =~ /ustar\s{0,2}\x00/).nil?
end


raw = ::File.open(archive_file_path, 'rb')

is_tar_archive?(raw)

[tas50]

Thanks for working this out and explaining it so well in the PR @bdwyertech

[bdwyertech]

You are welcome @tas50 -- Also I updated the PR on ChefDK to 0.4.16 so once this gets released, that should hopefully pass...