def call(env)
      start_time = Time.now.to_f
      time_elapsed = lambda { ((Time.now.to_f - start_time) * 1000).to_i }

      unless ALLOWED_REQUEST_METHODS.include? env['REQUEST_METHOD']
        return method_not_allowed_response
      end

      msg = "Served asset #{env['PATH_INFO']} -"

      # Extract the path from everything after the leading slash
      path = Rack::Utils.unescape(env['PATH_INFO'].to_s.sub(/^\//, ''))

      unless path.valid_encoding?
        return bad_request_response(env)
      end

      # Strip fingerprint
      if fingerprint = path_fingerprint(path)
        path = path.sub("-#{fingerprint}", '')
      end

      # URLs containing a `".."` are rejected for security reasons.
      if forbidden_request?(path)
        return forbidden_response(env)
      end

      if fingerprint
        if_match = fingerprint
      elsif env['HTTP_IF_MATCH']
        if_match = env['HTTP_IF_MATCH'][/"(\w+)"$/, 1]
      end

      if env['HTTP_IF_NONE_MATCH']
        if_none_match = env['HTTP_IF_NONE_MATCH'][/"(\w+)"$/, 1]
      end

      # Look up the asset.
      asset = find_asset(path)

      if asset.nil?
        status = :not_found
      elsif fingerprint && asset.etag != fingerprint
        status = :not_found
      elsif if_match && asset.etag != if_match
        status = :precondition_failed
      elsif if_none_match && asset.etag == if_none_match
        status = :not_modified
      else
        status = :ok
      end

      case status
      when :ok
        logger.info "#{msg} 200 OK (#{time_elapsed.call}ms)"
        ok_response(asset, env)
      when :not_modified
        logger.info "#{msg} 304 Not Modified (#{time_elapsed.call}ms)"
        not_modified_response(env, if_none_match)
      when :not_found
        logger.info "#{msg} 404 Not Found (#{time_elapsed.call}ms)"
        not_found_response(env)
      when :precondition_failed
        logger.info "#{msg} 412 Precondition Failed (#{time_elapsed.call}ms)"
        precondition_failed_response(env)
      end
    rescue Exception => e
      logger.error "Error compiling asset #{path}:"
      logger.error "#{e.class.name}: #{e.message}"

      case File.extname(path)
      when ".js"
        # Re-throw JavaScript asset exceptions to the browser
        logger.info "#{msg} 500 Internal Server Error\n\n"
        return javascript_exception_response(e)
      when ".css"
        # Display CSS asset exceptions in the browser
        logger.info "#{msg} 500 Internal Server Error\n\n"
        return css_exception_response(e)
      else
        raise
      end
    end
def call(env)
      start_time = Time.now.to_f
      time_elapsed = lambda { ((Time.now.to_f - start_time) * 1000).to_i }

      unless ALLOWED_REQUEST_METHODS.include? env['REQUEST_METHOD']
        return method_not_allowed_response
      end

      msg = "Served asset #{env['PATH_INFO']} -"

      # Extract the path from everything after the leading slash
      path = Rack::Utils.unescape(env['PATH_INFO'].to_s.sub(/^\//, ''))

      unless path.valid_encoding?
        return bad_request_response(env)
      end

      # Strip fingerprint
      if fingerprint = path_fingerprint(path)
        path = path.sub("-#{fingerprint}", '')
      end

      # URLs containing a `".."` are rejected for security reasons.
      if forbidden_request?(path)
        return forbidden_response(env)
      end

      if fingerprint
        if_match = fingerprint
      elsif env['HTTP_IF_MATCH']
        if_match = env['HTTP_IF_MATCH'][/"(\w+)"$/, 1]
      end

      if env['HTTP_IF_NONE_MATCH']
        if_none_match = env['HTTP_IF_NONE_MATCH'][/"(\w+)"$/, 1]
      end

      # Look up the asset.
      asset = find_asset(path)

      if asset.nil?
        status = :not_found
      elsif fingerprint && asset.etag != fingerprint
        status = :not_found
      elsif if_match && asset.etag != if_match
        status = :precondition_failed
      elsif if_none_match && asset.etag == if_none_match
        status = :not_modified
      else
        status = :ok
      end

      case status
      when :ok
        logger.info "#{msg} 200 OK (#{time_elapsed.call}ms)"
        ok_response(asset, env)
      when :not_modified
        logger.info "#{msg} 304 Not Modified (#{time_elapsed.call}ms)"
        not_modified_response(env, if_none_match)
      when :not_found
        logger.info "#{msg} 404 Not Found (#{time_elapsed.call}ms)"
        not_found_response(env)
      when :precondition_failed
        logger.info "#{msg} 412 Precondition Failed (#{time_elapsed.call}ms)"
        precondition_failed_response(env)
      end
    rescue Exception => e
      logger.error "Error compiling asset #{path}:"
      logger.error "#{e.class.name}: #{e.message}"

      case File.extname(path)
      when ".js"
        # Re-throw JavaScript asset exceptions to the browser
        logger.info "#{msg} 500 Internal Server Error\n\n"
        return javascript_exception_response(e)
      when ".css"
        # Display CSS asset exceptions in the browser
        logger.info "#{msg} 500 Internal Server Error\n\n"
        return css_exception_response(e)
      else
        raise
      end
    end
`call` implements the Rack 1.x specification which accepts an
 `env` Hash and returns a three item tuple with the status code,
 headers, and body.

 Mapping your environment at a url prefix will serve all assets
 in the path.

     map "/assets" do
       run Sprockets::Environment.new
     end

 A request for `"/assets/foo/bar.js"` will search your
 environment for `"foo/bar.js"`.