download

# File lib/rubygems/remote_fetcher.rb, line 115
  def download(spec, source_uri, install_dir = Gem.dir)
    cache_dir =
      if Dir.pwd == install_dir  # see fetch_command
        install_dir
      elsif File.writable? install_dir
        File.join install_dir, "cache"
      else
        File.join Gem.user_dir, "cache"
      end

    gem_file_name = File.basename spec.cache_file
    local_gem_path = File.join cache_dir, gem_file_name

    FileUtils.mkdir_p cache_dir rescue nil unless File.exist? cache_dir

    # Always escape URI's to deal with potential spaces and such
    # It should also be considered that source_uri may already be
    # a valid URI with escaped characters. e.g. "{DESede}" is encoded
    # as "%7BDESede%7D". If this is escaped again the percentage
    # symbols will be escaped.
    unless source_uri.is_a?(URI::Generic)
      begin
        source_uri = URI.parse(source_uri)
      rescue
        source_uri = URI.parse(URI::DEFAULT_PARSER.escape(source_uri.to_s))
      end
    end

    scheme = source_uri.scheme

    # URI.parse gets confused by MS Windows paths with forward slashes.
    scheme = nil if scheme =~ /^[a-z]$/

    # REFACTOR: split this up and dispatch on scheme (eg download_http)
    # REFACTOR: be sure to clean up fake fetcher when you do this... cleaner
    case scheme
    when 'http', 'https', 's3' then
      unless File.exist? local_gem_path
        begin
          verbose "Downloading gem #{gem_file_name}"

          remote_gem_path = source_uri + "gems/#{gem_file_name}"

          self.cache_update_path remote_gem_path, local_gem_path
        rescue Gem::RemoteFetcher::FetchError
          raise if spec.original_platform == spec.platform

          alternate_name = "#{spec.original_name}.gem"

          verbose "Failed, downloading gem #{alternate_name}"

          remote_gem_path = source_uri + "gems/#{alternate_name}"

          self.cache_update_path remote_gem_path, local_gem_path
        end
      end
    when 'file' then
      begin
        path = source_uri.path
        path = File.dirname(path) if File.extname(path) == '.gem'

        remote_gem_path = correct_for_windows_path(File.join(path, 'gems', gem_file_name))

        FileUtils.cp(remote_gem_path, local_gem_path)
      rescue Errno::EACCES
        local_gem_path = source_uri.to_s
      end

      verbose "Using local gem #{local_gem_path}"
    when nil then # TODO test for local overriding cache
      source_path = if Gem.win_platform? && source_uri.scheme &&
                       !source_uri.path.include?(':')
                      "#{source_uri.scheme}:#{source_uri.path}"
                    else
                      source_uri.path
                    end

      source_path = Gem::UriFormatter.new(source_path).unescape

      begin
        FileUtils.cp source_path, local_gem_path unless
          File.identical?(source_path, local_gem_path)
      rescue Errno::EACCES
        local_gem_path = source_uri.to_s
      end

      verbose "Using local gem #{local_gem_path}"
    else
      raise ArgumentError, "unsupported URI scheme #{source_uri.scheme}"
    end

    local_gem_path
  end