handlers.rb

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# Copyright (c) 2005 Zed A. Shaw 
# You can redistribute it and/or modify it under the same terms as Ruby.
#
# Additional work donated by contributors.  See http://mongrel.rubyforge.org/attributions.html 
# for more information.

require 'mongrel/stats'
require 'zlib'
require 'yaml'


module Mongrel

  # You implement your application handler with this.  It's very light giving
  # just the minimum necessary for you to handle a request and shoot back 
  # a response.  Look at the HttpRequest and HttpResponse objects for how
  # to use them.
  #
  # This is used for very simple handlers that don't require much to operate.
  # More extensive plugins or those you intend to distribute as GemPlugins 
  # should be implemented using the HttpHandlerPlugin mixin.
  #
  class HttpHandler
    attr_reader :request_notify
    attr_accessor :listener

    # This will be called by Mongrel if HttpHandler.request_notify set to *true*.
    # You only get the parameters for the request, with the idea that you'd "bound"
    # the beginning of the request processing and the first call to process.
    def request_begins(params)
    end

    # Called by Mongrel for each IO chunk that is received on the request socket
    # from the client, allowing you to track the progress of the IO and monitor
    # the input.  This will be called by Mongrel only if HttpHandler.request_notify
    # set to *true*.
    def request_progress(params, clen, total)
    end

    def process(request, response)
    end

  end


  # This is used when your handler is implemented as a GemPlugin.
  # The plugin always takes an options hash which you can modify
  # and then access later.  They are stored by default for 
  # the process method later.
  module HttpHandlerPlugin
    attr_reader :options
    attr_reader :request_notify
    attr_accessor :listener

    def request_begins(params)
    end

    def request_progress(params, clen, total)
    end

    def initialize(options={})
      @options = options
      @header_only = false
    end

    def process(request, response)
    end

  end


  # The server normally returns a 404 response if an unknown URI is requested, but it
  # also returns a lame empty message.  This lets you do a 404 response
  # with a custom message for special URIs.
  class Error404Handler < HttpHandler

    # Sets the message to return.  This is constructed once for the handler
    # so it's pretty efficient.
    def initialize(msg)
      @response = Const::ERROR_404_RESPONSE + msg
    end

    # Just kicks back the standard 404 response with your special message.
    def process(request, response)
      response.socket.write(@response)
    end

  end


  # Serves the contents of a directory.  You give it the path to the root
  # where the files are located, and it tries to find the files based on 
  # the PATH_INFO inside the directory.  If the requested path is a
  # directory then it returns a simple directory listing.
  #
  # It does a simple protection against going outside it's root path by
  # converting all paths to an absolute expanded path, and then making sure
  # that the final expanded path includes the root path.  If it doesn't
  # than it simply gives a 404.
  #
  # The default content type is "text/plain; charset=ISO-8859-1" but you
  # can change it anything you want using the DirHandler.default_content_type
  # attribute.
  class DirHandler < HttpHandler
    attr_accessor :default_content_type
    attr_reader :path

    MIME_TYPES_FILE = "mime_types.yml"
    MIME_TYPES = YAML.load_file(File.join(File.dirname(__FILE__), MIME_TYPES_FILE))

    ONLY_HEAD_GET="Only HEAD and GET allowed.".freeze

    # You give it the path to the directory root and an (optional) 
    def initialize(path, listing_allowed=true, index_html="index.html")
      @path = File.expand_path(path)
      @listing_allowed=listing_allowed
      @index_html = index_html
      @default_content_type = "application/octet-stream".freeze
    end

    # Checks if the given path can be served and returns the full path (or nil if not).
    def can_serve(path_info)
      req_path = File.expand_path(File.join(@path,HttpRequest.unescape(path_info)), @path)

      if req_path.index(@path) == 0 and File.exist? req_path
        # it exists and it's in the right location
        if File.directory? req_path
          # the request is for a directory
          index = File.join(req_path, @index_html)
          if File.exist? index
            # serve the index
            return index
          elsif @listing_allowed
            # serve the directory
            return req_path
          else
            # do not serve anything
            return nil
          end
        else
          # it's a file and it's there
          return req_path
        end
      else
        # does not exist or isn't in the right spot
        return nil
      end
    end


    # Returns a simplistic directory listing if they're enabled, otherwise a 403.
    # Base is the base URI from the REQUEST_URI, dir is the directory to serve 
    # on the file system (comes from can_serve()), and response is the HttpResponse
    # object to send the results on.
    def send_dir_listing(base, dir, response)
      # take off any trailing / so the links come out right
      base = HttpRequest.unescape(base)
      base.chop! if base[-1] == "/"[-1]

      if @listing_allowed
        response.start(200) do |head,out|
          head[Const::CONTENT_TYPE] = "text/html"
          out << "<html><head><title>Directory Listing</title></head><body>"
          Dir.entries(dir).each do |child|
            next if child == "."
            out << "<a href=\"#{base}/#{ HttpRequest.escape(child)}\">"
            out << (child == ".." ? "Up to parent.." : child)
            out << "</a><br/>"
          end
          out << "</body></html>"
        end
      else
        response.start(403) do |head,out|
          out.write("Directory listings not allowed")
        end
      end
    end


    # Sends the contents of a file back to the user. Not terribly efficient since it's
    # opening and closing the file for each read.
    def send_file(req_path, request, response, header_only=false)

      stat = File.stat(req_path)

      # Set the last modified times as well and etag for all files
      mtime = stat.mtime
      # Calculated the same as apache, not sure how well the works on win32
      etag = Const::ETAG_FORMAT % [mtime.to_i, stat.size, stat.ino]

      modified_since = request.params[Const::HTTP_IF_MODIFIED_SINCE]
      none_match = request.params[Const::HTTP_IF_NONE_MATCH]

      # test to see if this is a conditional request, and test if
      # the response would be identical to the last response
      same_response = case
                      when modified_since && !last_response_time = Time.httpdate(modified_since) rescue nil : false
                      when modified_since && last_response_time > Time.now                                  : false
                      when modified_since && mtime > last_response_time                                     : false
                      when none_match     && none_match == '*'                                              : false
                      when none_match     && !none_match.strip.split(/\s*,\s*/).include?(etag)              : false
                      else modified_since || none_match  # validation successful if we get this far and at least one of the header exists
                      end

      header = response.header
      header[Const::ETAG] = etag

      if same_response
        response.start(304) {}
      else
        # first we setup the headers and status then we do a very fast send on the socket directly
        response.status = 200
        header[Const::LAST_MODIFIED] = mtime.httpdate

        # set the mime type from our map based on the ending
        dot_at = req_path.rindex('.')
        if dot_at
          header[Const::CONTENT_TYPE] = MIME_TYPES[req_path[dot_at .. -1]] || @default_content_type
        else
          header[Const::CONTENT_TYPE] = @default_content_type
        end

        # send a status with out content length
        response.send_status(stat.size)
        response.send_header

        if not header_only