An HTTP importer for Sass

sass_http.rb

# Additional caching and such might be helpful for performance.
# Sass's regeneration only on changed files should work as long as the server provides the Last-Modified header

require 'net/http'
require 'time'
require 'sass'

module Sass
  module Importers
    # Importer which issues HTTP requests
    class HTTP < Base
      def initialize(root)
        @root = URI.parse(root)
        unless @root.absolute? && @root.scheme == 'http'
          raise ArgumentError, "Absolute HTTP URIs only"
        end
      end

      def find_relative(uri, base, options)
        _find(@root + base + uri, options)
      end

      def find(uri, options)
        _find(@root + uri, options)
      end

      def mtime(uri, options)
        uri = URI.parse(uri)
        return unless uri.absolute? && uri.scheme == 'http'
        Net::HTTP.start(uri.host, uri.port) do |http|
          response = http.head(uri.request_uri)

          if response.is_a?(Net::HTTPOK) && response['Last-Modified']
            Time.parse(response['Last-Modified'])
          elsif response.is_a? Net::HTTPOK
            # we must assume that it just changed
            Time.now
          else
            nil
          end
        end
      end

      def key(uri, options)
        [self.class.name, uri]
      end

      def to_s
        @root.to_s
      end

      protected

      def extensions
        {'.sass' => :sass, '.scss' => :scss}
      end

      private

      def exists?(uri)
        Net::HTTP.start(uri.host, uri.port) do |http|
          http.head(uri.request_uri).is_a? Net::HTTPOK
        end
      end

      def _find(uri, options)
        return unless uri.absolute? && uri.scheme == 'http'

        # determine the syntax being used
        ext = File.extname(uri.path)
        syntax = extensions[ext]

        # this must not be the full path: try another
        if syntax.nil?
          ext, syntax = extensions.find do |possible_ext, possible_syntax|
            new_uri = uri.dup
            new_uri.path += possible_ext
            exists? new_uri
          end

          return if syntax.nil?
          uri.path += ext
        end

        # fetch the content
        Net::HTTP.start(uri.host, uri.port) do |http|
          response = http.get(uri.request_uri)
          response.value

          options[:importer] = self
          options[:filename] = uri.to_s
          options[:syntax] = syntax
          Sass::Engine.new(response.body, options)
        end
      rescue
        nil
      end
    end
  end
end

Jeremy,
I had a great use for this the other day, and spent a day or so just packaging it up into a gem here: https://github.com/joeellis/remote-sass , complete with tests, README, some minor changes, etc. If it suits you, I'd like to add you in as an author as i didn't really make too many changes to your original code, so I believe you should have credit for that. Anyways, just let me know.