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diff --git a/jni/ruby/lib/rubygems/commands/unpack_command.rb b/jni/ruby/lib/rubygems/commands/unpack_command.rb
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+++ b/jni/ruby/lib/rubygems/commands/unpack_command.rb
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+require 'rubygems/command'
+require 'rubygems/installer'
+require 'rubygems/version_option'
+require 'rubygems/remote_fetcher'
+
+class Gem::Commands::UnpackCommand < Gem::Command
+
+  include Gem::VersionOption
+
+  def initialize
+    require 'fileutils'
+
+    super 'unpack', 'Unpack an installed gem to the current directory',
+          :version => Gem::Requirement.default,
+          :target  => Dir.pwd
+
+    add_option('--target=DIR',
+               'target directory for unpacking') do |value, options|
+      options[:target] = value
+    end
+
+    add_option('--spec', 'unpack the gem specification') do |value, options|
+      options[:spec] = true
+    end
+
+    add_version_option
+  end
+
+  def arguments # :nodoc:
+    "GEMNAME       name of gem to unpack"
+  end
+
+  def defaults_str # :nodoc:
+    "--version '#{Gem::Requirement.default}'"
+  end
+
+  def description
+    <<-EOF
+The unpack command allows you to examine the contents of a gem or modify
+them to help diagnose a bug.
+
+You can add the contents of the unpacked gem to the load path using the
+RUBYLIB environment variable or -I:
+
+  $ gem unpack my_gem
+  Unpacked gem: '.../my_gem-1.0'
+  [edit my_gem-1.0/lib/my_gem.rb]
+  $ ruby -Imy_gem-1.0/lib -S other_program
+
+You can repackage an unpacked gem using the build command.  See the build
+command help for an example.
+    EOF
+  end
+
+  def usage # :nodoc:
+    "#{program_name} GEMNAME"
+  end
+
+  #--
+  # TODO: allow, e.g., 'gem unpack rake-0.3.1'.  Find a general solution for
+  # this, so that it works for uninstall as well.  (And check other commands
+  # at the same time.)
+
+  def execute
+    get_all_gem_names.each do |name|
+      dependency = Gem::Dependency.new name, options[:version]
+      path = get_path dependency
+
+      unless path then
+        alert_error "Gem '#{name}' not installed nor fetchable."
+        next
+      end
+
+      if @options[:spec] then
+        spec, metadata = get_metadata path
+
+        if metadata.nil? then
+          alert_error "--spec is unsupported on '#{name}' (old format gem)"
+          next
+        end
+
+        spec_file = File.basename spec.spec_file
+
+        open spec_file, 'w' do |io|
+          io.write metadata
+        end
+      else
+        basename = File.basename path, '.gem'
+        target_dir = File.expand_path basename, options[:target]
+
+        package = Gem::Package.new path
+        package.extract_files target_dir
+
+        say "Unpacked gem: '#{target_dir}'"
+      end
+    end
+  end
+
+  ##
+  #
+  # Find cached filename in Gem.path. Returns nil if the file cannot be found.
+  #
+  #--
+  # TODO: see comments in get_path() about general service.
+
+  def find_in_cache(filename)
+    Gem.path.each do |path|
+      this_path = File.join(path, "cache", filename)
+      return this_path if File.exist? this_path
+    end
+
+    return nil
+  end
+
+  ##
+  # Return the full path to the cached gem file matching the given
+  # name and version requirement.  Returns 'nil' if no match.
+  #
+  # Example:
+  #
+  #   get_path 'rake', '> 0.4' # "/usr/lib/ruby/gems/1.8/cache/rake-0.4.2.gem"
+  #   get_path 'rake', '< 0.1' # nil
+  #   get_path 'rak'           # nil (exact name required)
+  #--
+  # TODO: This should be refactored so that it's a general service. I don't
+  # think any of our existing classes are the right place though.  Just maybe
+  # 'Cache'?
+  #
+  # TODO: It just uses Gem.dir for now.  What's an easy way to get the list of
+  # source directories?
+
+  def get_path dependency
+    return dependency.name if dependency.name =~ /\.gem$/i
+
+    specs = dependency.matching_specs
+
+    selected = specs.max_by { |s| s.version }
+
+    return Gem::RemoteFetcher.fetcher.download_to_cache(dependency) unless
+      selected
+
+    return unless dependency.name =~ /^#{selected.name}$/i
+
+    # We expect to find (basename).gem in the 'cache' directory.  Furthermore,
+    # the name match must be exact (ignoring case).
+
+    path = find_in_cache File.basename selected.cache_file
+
+    return Gem::RemoteFetcher.fetcher.download_to_cache(dependency) unless path
+
+    path
+  end
+
+  ##
+  # Extracts the Gem::Specification and raw metadata from the .gem file at
+  # +path+.
+  #--
+  # TODO move to Gem::Package as #raw_spec or something
+
+  def get_metadata path
+    format = Gem::Package.new path
+    spec = format.spec
+
+    metadata = nil
+
+    open path, Gem.binary_mode do |io|
+      tar = Gem::Package::TarReader.new io
+      tar.each_entry do |entry|
+        case entry.full_name
+        when 'metadata' then
+          metadata = entry.read
+        when 'metadata.gz' then
+          metadata = Gem.gunzip entry.read
+        end
+      end
+    end
+
+    return spec, metadata
+  end
+
+end
+