Add DOSTime#absolute_time?.

This method returns `true` if the time instance was created with accurate
timezone information. Ultimately, only those times parsed from binary
DOS format are missing accurate timezone information, but we need this
flag because ruby `Time` objects (from which `DOSTime` is decended) always
have a timezone set (usually whatever is local at the time).

lib/zip/dos_time.rb

@@ -16,6 +16,14 @@ class DOSTime < Time # :nodoc:all
     # bits 5-8 month (1-12)
     # bits 9-15 year (four digit year minus 1980)
 
+    attr_writer :absolute_time # :nodoc:
+
+    def absolute_time?
+      # If absolute time is not set, we can assume it is an absolute time
+      # because times do have timezone information by default.
+      @absolute_time.nil? ? true : @absolute_time
+    end
+
     def to_binary_dos_time
       (sec / 2) +
         (min << 5) +
@@ -53,7 +61,9 @@ def self.parse_binary_dos_format(bin_dos_date, bin_dos_time)
       month  = (0b111100000 & bin_dos_date) >> 5
       year   = ((0b1111111000000000 & bin_dos_date) >> 9) + 1980
 
-      local(year, month, day, hour, minute, second)
+      time = local(year, month, day, hour, minute, second)
+      time.absolute_time = false
+      time
     end
 
     if defined? JRUBY_VERSION && Gem::Version.new(JRUBY_VERSION) < '9.2.18.0'

test/dos_time_test.rb

@@ -0,0 +1,86 @@
+# frozen_string_literal: true
+
+require 'test_helper'
+require 'zip/dos_time'
+
+class DOSTimeTest < MiniTest::Test
+  def setup
+    @dos_time = Zip::DOSTime.new(2022, 1, 1, 12, 0, 0)
+  end
+
+  def test_new
+    dos_time = Zip::DOSTime.new
+    assert(dos_time.absolute_time?)
+
+    dos_time = Zip::DOSTime.new(2022, 1, 1, 12, 0, 0)
+    assert(dos_time.absolute_time?)
+
+    dos_time = Zip::DOSTime.new(2022, 1, 1, 12, 0, 0, 0)
+    assert(dos_time.absolute_time?)
+  end
+
+  def test_now
+    dos_time = Zip::DOSTime.now
+    assert(dos_time.absolute_time?)
+  end
+
+  def test_utc
+    dos_time = Zip::DOSTime.utc(2022, 1, 1, 12, 0, 0)
+    assert(dos_time.absolute_time?)
+  end
+
+  def test_gm
+    dos_time = Zip::DOSTime.gm(2022, 1, 1, 12, 0, 0)
+    assert(dos_time.absolute_time?)
+  end
+
+  def test_mktime
+    dos_time = Zip::DOSTime.mktime(2022, 1, 1, 12, 0, 0)
+    assert(dos_time.absolute_time?)
+  end
+
+  def test_from_time
+    time = Time.new(2022, 1, 1, 12, 0, 0)
+    dos_time = Zip::DOSTime.from_time(time)
+    assert_equal(@dos_time, dos_time)
+    assert(dos_time.absolute_time?)
+  end
+
+  def test_parse_binary_dos_format
+    bin_dos_date = 0b101010000100001
+    bin_dos_time = 0b110000000000000
+    dos_time = Zip::DOSTime.parse_binary_dos_format(bin_dos_date, bin_dos_time)
+    assert_equal(@dos_time, dos_time)
+    refute(dos_time.absolute_time?)
+  end
+
+  def test_at
+    time = Time.at(1_641_038_400)
+    dos_time = Zip::DOSTime.at(1_641_038_400)
+    assert_equal(time, dos_time)
+    assert(dos_time.absolute_time?)
+  end
+
+  def test_local
+    dos_time = Zip::DOSTime.local(2022, 1, 1, 12, 0, 0)
+    assert(dos_time.absolute_time?)
+  end
+
+  def test_comparison
+    time = Time.new(2022, 1, 1, 12, 0, 0)
+    assert_equal(0, @dos_time <=> time)
+  end
+
+  def test_jruby_cmp
+    return unless defined? JRUBY_VERSION && Gem::Version.new(JRUBY_VERSION) < '9.2.18.0'
+
+    time = Time.new(2022, 1, 1, 12, 0, 0)
+    assert(@dos_time == time)
+    assert(@dos_time <= time)
+    assert(@dos_time >= time)
+
+    time = Time.new(2022, 1, 1, 12, 1, 1)
+    assert(time > @dos_time)
+    assert(@dos_time < time)
+  end
+end