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diff --git a/trunk/lib/rubygems/indexer/abstract_index_builder.rb b/trunk/lib/rubygems/indexer/abstract_index_builder.rb
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+++ b/trunk/lib/rubygems/indexer/abstract_index_builder.rb
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+require 'zlib'
+
+require 'rubygems/indexer'
+
+# Abstract base class for building gem indicies.  Uses the template pattern
+# with subclass specialization in the +begin_index+, +end_index+ and +cleanup+
+# methods.
+class Gem::Indexer::AbstractIndexBuilder
+
+  # Directory to put index files in
+  attr_reader :directory
+
+  # File name of the generated index
+  attr_reader :filename
+
+  # List of written files/directories to move into production
+  attr_reader :files
+
+  def initialize(filename, directory)
+    @filename = filename
+    @directory = directory
+    @files = []
+  end
+
+  ##
+  # Build a Gem index.  Yields to block to handle the details of the
+  # actual building.  Calls +begin_index+, +end_index+ and +cleanup+ at
+  # appropriate times to customize basic operations.
+
+  def build
+    FileUtils.mkdir_p @directory unless File.exist? @directory
+    raise "not a directory: #{@directory}" unless File.directory? @directory
+
+    file_path = File.join @directory, @filename
+
+    @files << @filename
+
+    File.open file_path, "wb" do |file|
+      @file = file
+      start_index
+      yield
+      end_index
+    end
+
+    cleanup
+  ensure
+    @file = nil
+  end
+
+  ##
+  # Compress the given file.
+
+  def compress(filename, ext="rz")
+    data = open filename, 'rb' do |fp| fp.read end
+
+    zipped = zip data
+
+    File.open "#{filename}.#{ext}", "wb" do |file|
+      file.write zipped
+    end
+  end
+
+  # Called immediately before the yield in build.  The index file is open and
+  # available as @file.
+  def start_index
+  end
+
+  # Called immediately after the yield in build.  The index file is still open
+  # and available as @file.
+  def end_index
+  end
+
+  # Called from within builder after the index file has been closed.
+  def cleanup
+  end
+
+  # Return an uncompressed version of a compressed string.
+  def unzip(string)
+    Zlib::Inflate.inflate(string)
+  end
+
+  # Return a compressed version of the given string.
+  def zip(string)
+    Zlib::Deflate.deflate(string)
+  end
+
+end
+