S3 downloader (signed URL)

s3-downloader.rb

# encoding : utf-8
#!/usr/bin/env ruby
require 'openssl'
require 'digest/sha1'
require 'base64'
require 'date'
require 'uri'

class S3; end
class <<  S3
  def aws_access_key_id
    "YOUR_ACCESS_KEY"
  end
  def aws_secret_access_key
    "YOUR_SECRET_ACCESS_KEY"
  end

  def bucket
    "YOUR_BUCKET"
  end
end

module Aws
  extend self
  def signed_url(path, expire_date)
    digest = OpenSSL::Digest::Digest.new('sha1')
    can_string = "GET\n\n\n#{expire_date}\n/#{S3.bucket}/#{path}"
    hmac = OpenSSL::HMAC.digest(digest, S3.aws_secret_access_key, can_string)
    signature = URI.escape(Base64.encode64(hmac).strip).encode_signs
    "https://#{S3.bucket}.s3.amazonaws.com/#{path}?AWSAccessKeyId=#{S3.aws_access_key_id}&Expires=#{expire_date}&Signature=#{signature}"
  end
end

class String
  def encode_signs
    signs = {'+' => "%2B", '=' => "%3D", '?' => '%3F', '@' => '%40',
      '$' => '%24', '&' => '%26', ',' => '%2C', '/' => '%2F', ':' => '%3A',
      ';' => '%3B', '?' => '%3F'}
    signs.keys.each do |key|
      self.gsub!(key, signs[key])
    end
    self
  end
end

class Downloader
  def pathes
    (01..36).to_a.map{|x| "06/backup-20130106.gz.#{x.to_s.rjust(2, '0')}"}
  end

  def date
    @date ||= (Time.now + 10*60*60).to_i # expires in 10 hours
  end

  def signed_urls
    pathes.map do |path|
      signed_url = Aws.signed_url(path, date)
    end
  end

  def filename(url)
    File.basename(url.split('?').first)
  end

  def commands
    cmds = signed_urls.map do |url|
      fname   = filename(url)
      next if File.exists?(fname) and !File.exists?(fname + ".aria2") # download really finished
      #cmd = %Q{wget --no-check-certificate -O=#{filename} "#{url}"}
      cmd = %Q{aria2c -s 10  -o #{fname} "#{url}"}
    end
    (cmds - [nil])
  end

  def run(should_run=false)
    commands.each do |cmd|
      if should_run
        sh(cmd)
      else
        puts cmd
      end
    end
  end

  # simplified copy of rake`s sh
  def sh(cmd)
    puts cmd
    IO.popen(cmd) do |pipe|
      while str = pipe.gets
        puts str
      end
    end
    $?.success?
  end
end

should_run = ARGV[0] ? true : false
Downloader.new.run(should_run)