dan.thoughts

Amazon has an awesome image service. You can use their product images on your site, adjusting them for you needs. All you have to know – one image url of your product. Having that string will provide you an access to its dynamic image scaling service which i had to use recently.

So, lets say you have books on your website, but you dont have any good images for them. There is 2 ways to solve your problem: 1) download it from whatever place and resize 2) use amazon!

Here goes small overview.

Unfortunately, i didnt have any time to play with image service for different countries, but i assume that wont change that much. Lets take a look on a regular image:

http://ecx.images-amazon.com/images/I/41ygBmdaIfL._SL500_SS100_.jpg

It has different parts:
1) URL base: http://ecx.images-amazon.com/images/I/
2) Image code: 41ygBmdaIfL
3) Size format (surrounded by underscores): _SL500_SS100_
4) Format: jpg/gif/png

Some words about image format. It can vary from square thumbnails to images with specific max width and height. For example: _SX100_ will produce image that 100 pixels wide, height will be calculated proportionally. SH100 will give opposite result, scaled by 100 pixels maximum height, SS100 – 100×100 pixels thumbnail. And so on, you can find other similar crop codes while exploring amazon store on different pages, all you need is to take a look on image sources.

Now, we need to use this with Ruby:

require 'net/http'
 
module Amazon
  # parse amazon image url and get image code and extension
  def self.parse_image(url)
    result = url.scan(/^http:\/\/ecx.images-amazon.com\/images\/I\/([a-z0-9\-\%]{1,})(.*)_.(jpg|jpeg|gif)/i)
    unless result.nil?
      unless result[0].nil?
        match = result.first
        return {:code => match.first.to_s, :extension => match.last.to_s}
      end
    end
  end
 
  # make a new amazon image url based on code and size
  def self.make_image(image, size)
    "http://ecx.images-amazon.com/images/I/#{image[:code]}._#{size.upcase}.#{image[:extension]}"
  end
 
  # check if actual image exists
  def self.check_image(url)
    begin
      uri = URI.parse(url)
      req = Net::HTTP::Get.new(uri.path)
      res = Net::HTTP.start(uri.host, uri.port) { |http| http.request(req) }
      return res.code == '200' && res.content_length.to_i > 0
    rescue Exception
      false
    end
  end
end

And usage:

url = 'http://ecx.images-amazon.com/images/I/51O65dIoZCL._SX117_.jpg'
info = Amazon.parse_image(url)
unless info.nil?
  new_url = Amazon.make_image(info, 'sx100')
  if Amazon.check_image(new_url)
    puts "Cool! Resized image: #{new_url}"
  else
    puts "Sorry, this image does not exist!"
  end
else
  puts "Cant identify image!"
end

Some notes about the process. The only reason why method “check_image” uses GET method instead of HEAD is because if image cannot be generated or not found in amazon`s cache the response is still valid sometimes. I`ve checked it on 50k images and sometimes HEAD request indicates that response is valid while it not supposed to. Otherwise i would use HEAD.

For a long time i was thinking that Amazon`s Simple Storage Service (S3) is very complicated thing. But, it was before i tried it. Couple days ago, i got account to S3 and started exploring API`s and architecture. Now i see how stupid i was It`s really easy to handle all operations with files and buckets. Pricing also comfortable.

Welcome to cloud computing! I started using it with Ruby. Regular gem and docs can be found at http://amazon.rubyforge.org/

So, the first useful tool i decided to created – simple uploader of local files to amazons server.
First, we need to create bucket and make it public:

Bucket.create('NAME_HERE',:access => :public_read)

Here`s the client ruby script:

#!/usr/bin/ruby
 
require 'rubygems'
require 'aws/s3'
 
include AWS::S3
 
$s3_bucket = "BUCKET_NAME"
$s3_key = "API_KEY"
$s3_secret = "API_SECRET"
 
def s3_store(localfile)
	if File.exists?(localfile) && File.readable?(localfile)
		puts "Uploading file [#{localfile}]. Size: #{File.size(localfile)} bytes."
		name = File.basename(localfile)
		Base.establish_connection!(:access_key_id => $s3_key, :secret_access_key => $s3_secret)
		S3Object.store(name, open(localfile), $s3_bucket, :access => :public_read)
		puts "Download link: http://s3.amazonaws.com/#{$s3_bucket}/#{name}"
	else
		puts "File not exists or not accessible. Please check file and try again!"
	end
end
 
path = ARGV[0]
if !path
	"Please specify the file to upload."
else
	s3_store(path)
end

Download script: http://files.sosedoff.com/036cfedd/

BTW, I found cool firefox add-on to manage S3 objects/files. It`s pretty easy.
Link to extension – http://www.s3fox.net
Screenshot:

On my small project i was looking for web service to get media covers from. I found that i can use Amazon Web Services API. The documentation for this ECommerce Service is pretty old, but it still works.
More detailed information about API you can find here

#!/usr/bin/ruby
 
require 'rubygems'
require 'net/http'
require 'cgi'
require 'xmlsimple'
 
$amazon_key = "12DR2PGAQT303YTEWP02" # NOT MY KEY (FOUND ON INTERNET)
$amazon_host = "webservices.amazon.com"
 
def fetch_cover(artist, album)
	artist = CGI.escape(artist)
	album = CGI.escape(album)
 
	path = "/onca/xml?Service=AWSECommerceService&AWSAccessKeyId=#{$amazon_key}&Operation=ItemSearch&SearchIndex=Music&Artist=#{artist}&ResponseGroup=Images&Keywords=#{album}"
	data = Net::HTTP.get($amazon_host, path)
	xml = XmlSimple.xml_in(data)
	if xml['Items'][0]['TotalResults'].to_s.to_i then
		cover = {
			:small => xml['Items'][0]['Item'][0]['SmallImage'][0]['URL'],
			:medium => xml['Items'][0]['Item'][0]['MediumImage'][0]['URL'],
			:big => xml['Items'][0]['Item'][0]['LargeImage'][0]['URL']
		}
		return cover
	end
	return nil
end

So, after execution of this function you will get array with 3 different images (small, medium, big).
I use XML-Simple gem for ruby. Can be installed this way

sudo gem install xml-simple

That`s it. Download script