Function to compare package versions added

lib/deb_importer.rb

@@ -149,4 +149,71 @@ module DebImporter
     end # Enumerator
   end # def
 
+  # Determine which version string denotes the newer package
+  # v1: version of the first package
+  # v2: version of the second package
+  # op: the comparison operator (default: 'gt' / greater-than)
+  #
+  # The algorithm is described in the Debian Policy at
+  # https://www.debian.org/doc/debian-policy/ch-controlfields.html#s-f-Version
+  # The reference implementation is "dpkg --compare-versions …"
+  def dpkg_compare_version(v1, v2, op: 'gt')
+    system("dpkg --compare-versions #{v1} #{op} #{v2}")
+  end
+
+  class Version
+    def initialize(version_string)
+      @version_string = version_string
+      # Split into "[epoch:]version[-revision]"
+      unless version_string =~ /^(?<epoch>(\d+)\:)?(?<version>.+)(?<revision>\-[\+\.~]+)?/
+        raise ArgumentError, "Cannot parse version string: #{version_string}"
+      end
+      @epoch = epoch if epoch
+      @version = version
+      @revision = revision if revision
+    end # /def
+
+    def to_s
+      @version
+    end
+
+    def >(a,b)
+      return true if a.epoch > b.epoch
+      return true if version_compare(a.version, b.version)
+      return true if version_compare(a.revision, b.revision)
+    end
+
+    private
+
+    def version_compare(x,y)
+      # Compare a version string (like the upstream_version or
+      # debian_revision string) against another version string.
+      # The algorithm works like this:
+      #
+      # The strings are compared from left to right.
+      # First the initial part of each string consisting entirely of non-digit
+      # characters is determined. These two parts (one of which may be empty)
+      # are compared lexically. If a difference is found it is returned.
+      # The lexical comparison is a comparison of ASCII values modified so
+      # that all the letters sort earlier than all the non-letters and so that
+      # a tilde sorts before anything, even the end of a part.
+      # For example, the following parts are in sorted order from
+      # earliest to latest: ~~, ~~a, ~, the empty part, a.[37]
+      #
+      # Then the initial part of the remainder of each string which
+      # consists entirely of digit characters is determined. The
+      # numerical values of these two parts are compared, and any
+      # difference found is returned as the result of the comparison.
+      # For these purposes an empty string (which can only occur at
+      # the end of one or both version strings being compared) counts as zero.
+      #
+      # These two steps (comparing and removing initial non-digit strings
+      # and initial digit strings) are repeated until a difference is
+      # found or both strings are exhausted.
+
+      (x.chars).zip(y.chars) do |xchar,ychar|
+        puts xchar, ychar
+      end
+    end
+  end # /class
 end # module

test/lib/deb_importer_test.rb

@@ -8,10 +8,20 @@ include DebImporter
 
 class PackagesHelperTest < ActionView::TestCase
 
+  test "should detect the proper order of package versions" do
+    assert(DebImporter::Version.new('2') > DebImporter::Version.new('1'))
+    assert(DebImporter::Version.new('1.0') > DebImporter::Version.new('0.9'))
+    assert(DebImporter::Version.new('2:1') > DebImporter::Version.new('1:2'))
+    assert(DebImporter::Version.new('1.0c') > DebImporter::Version.new('1.0aa'))
+    assert(DebImporter::Version.new('1.0.1') > DebImporter::Version.new('1.0.0.1'))
+    assert(DebImporter::Version.new('1.0c') > DebImporter::Version.new('1.0.0'))
+    assert(DebImporter::Version.new('1.0') > DebImporter::Version.new('1.0~pre'))
+  end
+
   test "should be able to parse local Debian repository test files" do
     Rails.logger = Logger.new(STDOUT)
-    Rails.logger.level = Logger::ERROR
+    # Rails.logger.level = Logger::ERROR
-    # Rails.logger.level = Logger::INFO
+    Rails.logger.level = Logger::INFO
     # Rails.logger.level = Logger::DEBUG
 
     # Load information about test repository from environments/test.rb