A ruby method to quickly generate s3 direct upload hash

s3_directupload_helper.gemspec

Gem::Specification.new do |s|
  s.name        = 's3-directupload-helper'
  s.version     = '0.0.1'
  s.platform    = Gem::Platform::RUBY
  s.author      = 'Raykin'
  s.email       = 'raykincoldxiao@gmail.com'
  s.summary     = 'easy create s3 directupload form in rails'
  s.description = 'clear and easy'
  s.files         = ['s3_directupload_helper.rb']
  s.require_path  = '.'
end

s3_directupload_helper.rb

module S3DirectuploadHelper

  class AccessConfig < Struct.new(:access_key_id, :secret_access_key, :bucket, :region)
    include Singleton
  end

  # setup s3 config in config/initializers/an_override_file.rb works
  def self.access_config
    if block_given?
      yield AccessConfig.instance
    end
    AccessConfig.instance
  end

  def self.access_config_blank?
    access_config.access_key_id.nil?
  end

  # setup s3 config by ENV works too
  def self.init_access_config
    access_config do |config|
      config.access_key_id     = ENV['s3_access_key_id'] || ENV['S3_ACCESS_KEY_ID']
      config.secret_access_key = ENV['s3_secret_access_key'] || ENV['S3_SECRET_ACCESS_KEY']
      config.bucket            = ENV['s3_bucket'] || ENV['S3_BUCKET']
    end
  end

  class Uploader
    def initialize(options)
      S3DirectuploadHelper.init_access_config if S3DirectuploadHelper.access_config_blank?
      @options = options.reverse_merge(
                                       aws_access_key_id: S3DirectuploadHelper.access_config.access_key_id,
                                       aws_secret_access_key: S3DirectuploadHelper.access_config.secret_access_key,
                                       bucket: S3DirectuploadHelper.access_config.bucket,
                                       region: S3DirectuploadHelper.access_config.region || "s3",
                                       acl: "public-read",
                                       expiration: 10.hours.from_now.utc.iso8601,
                                       max_file_size: 500.megabytes,
                                       as: "file",
                                       key: default_key
                                       )
    end

    def form_options
      {
        id: @options[:id],
        class: @options[:class],
        method: "post",
        authenticity_token: false,
        multipart: true,
        data: {
          post: @options[:post],
          as: @options[:as]
        }.reverse_merge(@options[:data] || {})
      }
    end

    def fields
      {
        :key => @options[:key] || default_key,
        :acl => @options[:acl],
        "AWSAccessKeyId" => @options[:aws_access_key_id],
        :policy => policy,
        :signature => signature,
        :success_action_status => "201",
        'X-Requested-With' => 'xhr',
        :utf8 => true,
        'Content-Type' => ''
      }
    end

    def default_key
      @key ||= "uploads/#{DateTime.now.utc.strftime("%Y%m%dT%H%MZ")}_#{SecureRandom.hex}/${filename}"
    end

    def url
      "https://#{@options[:region]}.amazonaws.com/#{@options[:bucket]}/"
    end

    def policy
      Base64.encode64(policy_data.to_json).gsub("\n", "")
    end

    def policy_data
      @policy_data ||= {
        expiration: @options[:expiration],
        conditions: [
                     ["starts-with", "$utf8", ""],
                     ["starts-with", "$key", ""],
                     ["starts-with", "$x-requested-with", ""],
                     ["content-length-range", 0, @options[:max_file_size]],
                     ["starts-with","$Content-Type",""],
                     {bucket: @options[:bucket]},
                     {acl: @options[:acl]},
                     {success_action_status: "201"}
                    ]
      }
    end

    def add_success_action_redirect(url)
      policy_data[:conditions] << { success_action_redirect: url }
    end

    def signature
      Base64.encode64(
                      OpenSSL::HMAC.digest(
                                           OpenSSL::Digest.new('sha1'),
                                           @options[:aws_secret_access_key], policy
                                           )
                      ).gsub("\n", "")
    end
  end

end

usage.md

Usage:

include gem 's3-directupload-helper', :git => "git://gist.github.com/5202809.git", :require => "s3_directupload_helper" in your Gemfile

S3DirectuploadHelper::Uploader.new({}).fields contains the signature.