Question

Im looking for a way to map an ActiveResource to SimpleDB

I want to avoid plugins/gems as all I have used are outdated/buggy/not mantained

It doesnt seem hard, I wonder if any of you have succesfully implemented a rails app with simpleDB as an Active Resource. How did you do it? Thanks.

Answer 1

I haven’t worked with SimpleDB, but I have mapped ActiveResource to Amazon’s Flexible Payments Service REST api and just skimming the docs they seem similar so here’s basically what I did, maybe you can use this as a starting point.

require 'base64'
require 'openssl'

class AmazonFlexiblePaymentResource < ActiveResource::Base
  self.site = AMZ_CONFIG['flexible_api_url']

  def self.rest_api(options = {})
    params = common_request_params.update(options)

    sig = compute_signature(AMZ_CONFIG['secret_access_key'], 'get', site, params)

    rest_req = {'Signature' => sig}.update(params)

    # make the http get call
    connection.get("/#{query_string(rest_req)}", headers)
  end

  protected

  # these are the params are common to all rest api calls
  def self.common_request_params
    { 'AWSAccessKeyId' => AMZ_CONFIG['access_key_id'],
      'SignatureVersion' => 2,
      'SignatureMethod' => 'HmacSHA256',
      'Timestamp' => Time.now.utc.iso8601,
      'Version' => '2008-09-17'}
  end

  def self.compute_signature(key, method, end_point_url, params)
    query_str = parameters.sort.collect {|k, v| v.to_query(k)}.join '&'

    # cannot use plus for space, and tilde needs to be reversed
    query_str.gsub!('+', '%20')
    query_str.gsub!('%7E', '~')

    to_sign = [method.upcase, end_point_uri.host.downcase,
        end_point_uri.request_uri, query_str].join "\n"

    digest = OpenSSL::Digest::Digest.new('sha256')
    hmac = OpenSSL::HMAC.digest(digest, key, to_sign)
    Base64.encode64(hmac).chomp
  end
end

Then I just make calls like this

res = AmazonFlexiblePaymentResource.rest_api({ 'Action' => 'GetTransactionStatus', 'TransactionId' => '1234567890ABCDEFGHIJ' })

And the response is a hash of the parsed xml. Again this works for Amazon Flexible Payments Service, so you may need to make adjustments to match the SimpleDB REST API.