Extending Web Services Using Other Web Services

Listing 3. xmlrpc-lookup.rb

#!/usr/bin/ruby

require 'net/http'
require 'rexml/document'
require 'xmlrpc/server'

# Set our regular expressions
not_in_collection_re = /class="yourEntryWouldBeHereData"/ix
on_shelf_re = /CHECK\s+SHELF/ix
checked_out_re = /DUE /ix

# ------------------------------------------------------------
# XML-RPC
# ------------------------------------------------------------

# Start an HTTP server on port 8080, to listen for clients
server = XMLRPC::Server.new(8080)

server.add_handler(name="atf.books",
                   signature=['array', 'array']) do |isbns|

  output = [ ]

  # Iterate through each of our arguments
  isbns.each do |isbn|

    isbn_output = {'ISBN' => isbn}

    # Ignore non-ISBN arguments
    if not isbn.match(/^[0-9xX]{10}$/)
      isbn_output['message'] = "ISBN #{isbn} is invalid."
      output << isbn_output
      next
    end

    # ------------------------------------------------------------
    # Amazon
    # ------------------------------------------------------------

    # Put together an Amazon parameter string
    amazon_params = {'Service' => 'AWSECommerceService',
      'Operation' => 'ItemLookup',
      'AWSAccessKeyId' => 'XXX',
      'ItemId' => isbn,
      'ResponseGroup' => 'Medium,OfferFull',
      'MerchantId' => 'All'}.map {|key,value|
"#{key}=#{value}"}.join("&")

    # Ask Amazon what it knows about our ISBN
    amazon_response = Net::HTTP.get_response('webservices.amazon.com',
                                             '/onca/xml?' <<
amazon_params)

    xml = REXML::Document.new(amazon_response.body)

    # Get the lowest new, used, and collectible prices
    new_price =
xml.root.elements["Items/Item/OfferSummary/LowestNewPrice/FormattedPrice"]
    if new_price.nil?
      isbn_output['New'] = "None available"
    else
      isbn_output['New'] = new_price.text
    end

    used_price =
xml.root.elements["Items/Item/OfferSummary/LowestUsedPrice/FormattedPrice"]
    if used_price.nil?
      isbn_output['Used'] = "None available"
    else
      isbn_output['Used'] = used_price.text
    end

    collectible_price =
xml.root.elements["Items/Item/OfferSummary/LowestCollectiblePrice/FormattedPrice"]
    if collectible_price.nil?
      isbn_output['Collectible'] = "None available"
    else
      isbn_output['Collectible'] = collectible_price.text
    end

    # ------------------------------------------------------------
    # Library
    # ------------------------------------------------------------

    # Ask the library what it knows about our ISBN
    library_response = Net::HTTP.get_response('catalog.skokie.lib.il.us',
                                              "/search~S4/i?SEARCH=#{isbn}")

    # Check our regular expressions against the HTML response
    if not_in_collection_re.match(library_response.body)
      isbn_output['Library'] = "Library: Not in the Skokie collection."
    elsif checked_out_re.match(library_response.body)
      isbn_output['Library'] = "Checked out."
    elsif on_shelf_re.match(library_response.body)
      isbn_output['Library'] = "On the shelf."
    else
      isbn_output['Library'] = "Unparseable response."
    end

    output << isbn_output
  end

  output
end

server.serve