diff --git a/.travis.yml b/.travis.yml
index 52e1d3436..47d00e916 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -1,20 +1,12 @@
 rvm:
-  - 2.0
   - 2.1
   - 2.2
 
 script: "bundle exec rake clean spec cucumber"
 
 gemfile:
-  - gemfiles/3.2.awsv2.1.gemfile
-  - gemfiles/4.1.awsv2.1.gemfile
   - gemfiles/4.2.awsv2.1.gemfile
-  - gemfiles/3.2.awsv2.0.gemfile
-  - gemfiles/4.1.awsv2.0.gemfile
   - gemfiles/4.2.awsv2.0.gemfile
-  - gemfiles/3.2.awsv1.gemfile
-  - gemfiles/4.1.awsv1.gemfile
-  - gemfiles/4.2.awsv1.gemfile
 
 sudo: false
 cache: bundler
diff --git a/Appraisals b/Appraisals
index 240977dd6..bdfd8bbc0 100644
--- a/Appraisals
+++ b/Appraisals
@@ -1,44 +1,17 @@
-appraise "3.2.awsv2.1" do
-  gem "rails", "~> 3.2.0"
-  gem "aws-sdk", "~> 2.1.0"
-end
-
-appraise "4.1.awsv2.1" do
-  gem "rails", "~> 4.1.0"
-  gem "aws-sdk", "~> 2.1.0"
-end
-
 appraise "4.2.awsv2.1" do
   gem "rails", "~> 4.2.0"
-  gem "aws-sdk", "~> 2.1.0"
-end
-
-appraise "3.2.awsv2.0" do
-  gem "rails", "~> 3.2.0"
-  gem "aws-sdk", "~> 2.0.0"
-end
+  gem "aws-sdk-s3", "~> 1"
 
-appraise "4.1.awsv2.0" do
-  gem "rails", "~> 4.1.0"
-  gem "aws-sdk", "~> 2.0.0"
+  group :development, :test do
+    gem 'mime-types', '>= 1.16', '< 4'
+  end
 end
 
 appraise "4.2.awsv2.0" do
   gem "rails", "~> 4.2.0"
-  gem "aws-sdk", "~> 2.0.0"
-end
-
-appraise "3.2.awsv1" do
-  gem "rails", "~> 3.2.0"
-  gem "aws-sdk", "~> 1.5"
-end
+  gem "aws-sdk-s3", "~> 1"
 
-appraise "4.1.awsv1" do
-  gem "rails", "~> 4.1.0"
-  gem "aws-sdk", "~> 1.5"
-end
-
-appraise "4.2.awsv1" do
-  gem "rails", "~> 4.2.0"
-  gem "aws-sdk", "~> 1.5"
+  group :development, :test do
+    gem 'mime-types', '>= 1.16', '< 4'
+  end
 end
diff --git a/Gemfile b/Gemfile
index bdeb5f71b..98ee80d44 100644
--- a/Gemfile
+++ b/Gemfile
@@ -9,7 +9,7 @@ gem 'pry'
 # Prevents bundler from taking a long-time to resolve
 group :development, :test do
   gem 'activerecord-import'
-  gem 'mime-types', '~> 1.16'
+  gem 'mime-types'
   gem 'builder'
   gem 'rubocop', require: false
 end
diff --git a/LICENSE b/LICENSE
index 49c7d45a3..68bcce33f 100644
--- a/LICENSE
+++ b/LICENSE
@@ -3,7 +3,7 @@ LICENSE
 
 The MIT License
 
-Copyright (c) 2008-2015 Jon Yurek and thoughtbot, inc.
+Copyright (c) 2008-2016 Jon Yurek and thoughtbot, inc.
 
 Permission is hereby granted, free of charge, to any person obtaining a copy
 of this software and associated documentation files (the "Software"), to deal
diff --git a/NEWS b/NEWS
index dc8ada6b3..c50a24e49 100644
--- a/NEWS
+++ b/NEWS
@@ -1,5 +1,6 @@
 master:
 
+* Drops support to end-of-life'd ruby 2.0.
 * Improvement: Paperclip now supports aws-sdk v2
   @betesh, @davetchen,
   https://github.com/thoughtbot/paperclip/pull/1903
@@ -9,14 +10,10 @@ master:
   s3_region may be nested in s3_credentials, and (if not nested in
   s3_credentials) it may be a Proc.
 
-4.3.1 (2015-09-09):
+4.3
 
-* Backport of bugfix to `remove_column`, so it works in Rails 3 and 4
-  c740fb171fe2f88c60b999d2a1c2122f2b8f43e9
-* Fix GeometryParser regex for usage of '@>' flag
-* `url` on a unpersisted record returns default_url
-* spec deprecation warnings and failures
-* README adjustments
+See patch versions in v4.3 NEWS:
+https://github.com/thoughtbot/paperclip/blob/v4.3/NEWS
 
 4.3.0 (2015-06-18):
 
diff --git a/README.md b/README.md
index 4191dd4a9..d66b6f64f 100644
--- a/README.md
+++ b/README.md
@@ -22,6 +22,7 @@ Paperclip
   - [Deleting an Attachment](#deleting-an-attachment)
 - [Usage](#usage)
 - [Validations](#validations)
+- [Internationalization (I18n)](#internationalization-i18n)
 - [Security Validations](#security-validations)
 - [Defaults](#defaults)
 - [Migrations](#migrations-1)
@@ -400,6 +401,12 @@ inferred content_type, regardless of the actual contents of the file.
 
 ---
 
+Internationalization (I18n)
+---------------------------
+
+For using or adding locale files in different languages, check the project
+https://github.com/thoughtbot/paperclip-i18n.
+
 Security Validations
 ====================
 
@@ -554,7 +561,7 @@ Storage
 Paperclip ships with 3 storage adapters:
 
 * File Storage
-* S3 Storage (via `aws-sdk` or `aws-sdk-v1`)
+* S3 Storage (via `aws-sdk`)
 * Fog Storage
 
 If you would like to use Paperclip with another storage, you can install these
@@ -584,10 +591,6 @@ the `aws-sdk` gem in your Gemfile:
 ```ruby
 gem 'aws-sdk', '>= 2.0.0' # If using paperclip `master` (upcoming v5.0)
 ```
-or
-```ruby
-gem 'aws-sdk-v1' # If using paperclip <= v4.3.1
-```
 
 And then you can specify using S3 from `has_attached_file`.
 You can find more information about configuring and using S3 storage in
@@ -967,7 +970,7 @@ Thank you to all [the contributors](https://github.com/thoughtbot/paperclip/grap
 License
 -------
 
-Paperclip is Copyright © 2008-2015 thoughtbot, inc. It is free software, and may be
+Paperclip is Copyright © 2008-2016 thoughtbot, inc. It is free software, and may be
 redistributed under the terms specified in the MIT-LICENSE file.
 
 About thoughtbot
diff --git a/UPGRADING b/UPGRADING
index 44a2739a3..d997a83b6 100644
--- a/UPGRADING
+++ b/UPGRADING
@@ -12,8 +12,3 @@ changes:
   note that the format of the permissions changed from using an underscore to
   using a hyphen. For example, `:public_read` needs to be changed to
   `public-read`.
-
-If you want to continue using an earlier version of aws-sdk, replace
- aws-sdk with aws-sdk-v1 in your Gemfile.
-
-If both are in your Gemfile, paperclip will use aws-sdk v2.
diff --git a/gemfiles/3.2.awsv1.gemfile b/gemfiles/3.2.awsv1.gemfile
deleted file mode 100644
index a40423302..000000000
--- a/gemfiles/3.2.awsv1.gemfile
+++ /dev/null
@@ -1,17 +0,0 @@
-# This file was generated by Appraisal
-
-source "https://rubygems.org"
-
-gem "sqlite3", "~> 1.3.8", platforms: :ruby
-gem "pry"
-gem "rails", "~> 3.2.0"
-gem "aws-sdk", "~> 1.5"
-
-group :development, :test do
-  gem "activerecord-import"
-  gem "mime-types", "~> 1.16"
-  gem "builder"
-  gem "rubocop", :require => false
-end
-
-gemspec path: "../"
diff --git a/gemfiles/3.2.awsv2.0.gemfile b/gemfiles/3.2.awsv2.0.gemfile
deleted file mode 100644
index 8c7cd14a8..000000000
--- a/gemfiles/3.2.awsv2.0.gemfile
+++ /dev/null
@@ -1,17 +0,0 @@
-# This file was generated by Appraisal
-
-source "https://rubygems.org"
-
-gem "sqlite3", "~> 1.3.8", platforms: :ruby
-gem "pry"
-gem "rails", "~> 3.2.0"
-gem "aws-sdk", "~> 2.0.0"
-
-group :development, :test do
-  gem "activerecord-import"
-  gem "mime-types", "~> 1.16"
-  gem "builder"
-  gem "rubocop", :require => false
-end
-
-gemspec path: "../"
diff --git a/gemfiles/3.2.awsv2.1.gemfile b/gemfiles/3.2.awsv2.1.gemfile
deleted file mode 100644
index 1b586574c..000000000
--- a/gemfiles/3.2.awsv2.1.gemfile
+++ /dev/null
@@ -1,17 +0,0 @@
-# This file was generated by Appraisal
-
-source "https://rubygems.org"
-
-gem "sqlite3", "~> 1.3.8", platforms: :ruby
-gem "pry"
-gem "rails", "~> 3.2.0"
-gem "aws-sdk", "~> 2.1.0"
-
-group :development, :test do
-  gem "activerecord-import"
-  gem "mime-types", "~> 1.16"
-  gem "builder"
-  gem "rubocop", :require => false
-end
-
-gemspec path: "../"
diff --git a/gemfiles/4.1.awsv1.gemfile b/gemfiles/4.1.awsv1.gemfile
deleted file mode 100644
index 278659d4b..000000000
--- a/gemfiles/4.1.awsv1.gemfile
+++ /dev/null
@@ -1,17 +0,0 @@
-# This file was generated by Appraisal
-
-source "https://rubygems.org"
-
-gem "sqlite3", "~> 1.3.8", platforms: :ruby
-gem "pry"
-gem "rails", "~> 4.1.0"
-gem "aws-sdk", "~> 1.5"
-
-group :development, :test do
-  gem "activerecord-import"
-  gem "mime-types", "~> 1.16"
-  gem "builder"
-  gem "rubocop", :require => false
-end
-
-gemspec path: "../"
diff --git a/gemfiles/4.1.awsv2.0.gemfile b/gemfiles/4.1.awsv2.0.gemfile
deleted file mode 100644
index 7295e2937..000000000
--- a/gemfiles/4.1.awsv2.0.gemfile
+++ /dev/null
@@ -1,17 +0,0 @@
-# This file was generated by Appraisal
-
-source "https://rubygems.org"
-
-gem "sqlite3", "~> 1.3.8", platforms: :ruby
-gem "pry"
-gem "rails", "~> 4.1.0"
-gem "aws-sdk", "~> 2.0.0"
-
-group :development, :test do
-  gem "activerecord-import"
-  gem "mime-types", "~> 1.16"
-  gem "builder"
-  gem "rubocop", :require => false
-end
-
-gemspec path: "../"
diff --git a/gemfiles/4.1.awsv2.1.gemfile b/gemfiles/4.1.awsv2.1.gemfile
deleted file mode 100644
index 9ab82b0ca..000000000
--- a/gemfiles/4.1.awsv2.1.gemfile
+++ /dev/null
@@ -1,17 +0,0 @@
-# This file was generated by Appraisal
-
-source "https://rubygems.org"
-
-gem "sqlite3", "~> 1.3.8", platforms: :ruby
-gem "pry"
-gem "rails", "~> 4.1.0"
-gem "aws-sdk", "~> 2.1.0"
-
-group :development, :test do
-  gem "activerecord-import"
-  gem "mime-types", "~> 1.16"
-  gem "builder"
-  gem "rubocop", :require => false
-end
-
-gemspec path: "../"
diff --git a/gemfiles/4.2.awsv1.gemfile b/gemfiles/4.2.awsv1.gemfile
deleted file mode 100644
index 8b423c951..000000000
--- a/gemfiles/4.2.awsv1.gemfile
+++ /dev/null
@@ -1,17 +0,0 @@
-# This file was generated by Appraisal
-
-source "https://rubygems.org"
-
-gem "sqlite3", "~> 1.3.8", platforms: :ruby
-gem "pry"
-gem "rails", "~> 4.2.0"
-gem "aws-sdk", "~> 1.5"
-
-group :development, :test do
-  gem "activerecord-import"
-  gem "mime-types", "~> 1.16"
-  gem "builder"
-  gem "rubocop", :require => false
-end
-
-gemspec path: "../"
diff --git a/gemfiles/4.2.awsv2.0.gemfile b/gemfiles/4.2.awsv2.0.gemfile
index 528906aec..ef705dfd6 100644
--- a/gemfiles/4.2.awsv2.0.gemfile
+++ b/gemfiles/4.2.awsv2.0.gemfile
@@ -9,7 +9,7 @@ gem "aws-sdk", "~> 2.0.0"
 
 group :development, :test do
   gem "activerecord-import"
-  gem "mime-types", "~> 1.16"
+  gem "mime-types", ">= 1.16", "< 4"
   gem "builder"
   gem "rubocop", :require => false
 end
diff --git a/gemfiles/4.2.awsv2.1.gemfile b/gemfiles/4.2.awsv2.1.gemfile
index 361cfa09c..9b52119cf 100644
--- a/gemfiles/4.2.awsv2.1.gemfile
+++ b/gemfiles/4.2.awsv2.1.gemfile
@@ -9,7 +9,7 @@ gem "aws-sdk", "~> 2.1.0"
 
 group :development, :test do
   gem "activerecord-import"
-  gem "mime-types", "~> 1.16"
+  gem "mime-types", ">= 1.16", "< 4"
   gem "builder"
   gem "rubocop", :require => false
 end
diff --git a/lib/paperclip/attachment.rb b/lib/paperclip/attachment.rb
index 87f26d5a8..9dcf72754 100644
--- a/lib/paperclip/attachment.rb
+++ b/lib/paperclip/attachment.rb
@@ -427,7 +427,7 @@ def initialize_storage #:nodoc:
     def assign_attributes
       @queued_for_write[:original] = @file
       assign_file_information
-      assign_fingerprint(@file.fingerprint)
+      assign_fingerprint { @file.fingerprint }
       assign_timestamps
     end
 
@@ -437,9 +437,9 @@ def assign_file_information
       instance_write(:file_size, @file.size)
     end
 
-    def assign_fingerprint(fingerprint)
+    def assign_fingerprint
       if instance_respond_to?(:fingerprint)
-        instance_write(:fingerprint, fingerprint)
+        instance_write(:fingerprint, yield)
       end
     end
 
@@ -465,7 +465,7 @@ def dirty!
 
     def reset_file_if_original_reprocessed
       instance_write(:file_size, @queued_for_write[:original].size)
-      assign_fingerprint(@queued_for_write[:original].fingerprint)
+      assign_fingerprint { @queued_for_write[:original].fingerprint }
       reset_updater
     end
 
@@ -523,6 +523,10 @@ def post_process_style(name, style) #:nodoc:
         @queued_for_write[name] = style.processors.inject(@queued_for_write[:original]) do |file, processor|
           file = Paperclip.processor(processor).make(file, style.processor_options, self)
           intermediate_files << file unless file == @queued_for_write[:original]
+          # if we're processing the original, close + unlink the source tempfile
+          if name == :original
+            @queued_for_write[:original].close(true)
+          end
           file
         end
 
diff --git a/lib/paperclip/content_type_detector.rb b/lib/paperclip/content_type_detector.rb
index 782ed9e7c..6c98baada 100644
--- a/lib/paperclip/content_type_detector.rb
+++ b/lib/paperclip/content_type_detector.rb
@@ -50,17 +50,22 @@ def empty_file?
     alias :empty? :empty_file?
 
     def calculated_type_matches
-      possible_types.select do |content_type|
-        content_type == type_from_file_contents
-      end
+      possible_types & types_from_file_contents
     end
 
     def possible_types
       MIME::Types.type_for(@filepath).collect(&:content_type)
     end
 
+    def types_from_file_contents
+      [type_from_file_command, type_from_mime_magic].compact
+    rescue Errno::ENOENT => e
+      Paperclip.log("Error while determining content type: #{e}")
+      SENSIBLE_DEFAULT
+    end
+
     def type_from_file_contents
-      type_from_mime_magic || type_from_file_command
+      type_from_file_command || type_from_mime_magic
     rescue Errno::ENOENT => e
       Paperclip.log("Error while determining content type: #{e}")
       SENSIBLE_DEFAULT
diff --git a/lib/paperclip/glue.rb b/lib/paperclip/glue.rb
index 2d14c627a..c8d9e89a3 100644
--- a/lib/paperclip/glue.rb
+++ b/lib/paperclip/glue.rb
@@ -8,7 +8,7 @@ def self.included(base)
       base.extend ClassMethods
       base.send :include, Callbacks
       base.send :include, Validators
-      base.send :include, Schema if defined? ActiveRecord
+      base.send :include, Schema if defined? ActiveRecord::Base
 
       locale_path = Dir.glob(File.dirname(__FILE__) + "/locales/*.{rb,yml}")
       I18n.load_path += locale_path unless I18n.load_path.include?(locale_path)
diff --git a/lib/paperclip/io_adapters/abstract_adapter.rb b/lib/paperclip/io_adapters/abstract_adapter.rb
index 189778e67..ada5dbe96 100644
--- a/lib/paperclip/io_adapters/abstract_adapter.rb
+++ b/lib/paperclip/io_adapters/abstract_adapter.rb
@@ -4,7 +4,7 @@ module Paperclip
   class AbstractAdapter
     OS_RESTRICTED_CHARACTERS = %r{[/:]}
 
-    attr_reader :content_type, :original_filename, :size
+    attr_reader :content_type, :original_filename, :size, :tempfile
     delegate :binmode, :binmode?, :close, :close!, :closed?, :eof?, :path, :rewind, :unlink, :to => :@tempfile
     alias :length :size
 
diff --git a/lib/paperclip/io_adapters/attachment_adapter.rb b/lib/paperclip/io_adapters/attachment_adapter.rb
index 8319617f6..ff7695082 100644
--- a/lib/paperclip/io_adapters/attachment_adapter.rb
+++ b/lib/paperclip/io_adapters/attachment_adapter.rb
@@ -24,7 +24,13 @@ def copy_to_tempfile(source)
       if source.staged?
         FileUtils.cp(source.staged_path(@style), destination.path)
       else
-        source.copy_to_local_file(@style, destination.path)
+        begin
+          source.copy_to_local_file(@style, destination.path)
+        rescue Errno::EACCES => e
+          # clean up lingering tempfile if we cannot access source file
+          destination.close(true)
+          raise
+        end
       end
       destination
     end
diff --git a/lib/paperclip/schema.rb b/lib/paperclip/schema.rb
index dafb715f9..311d23920 100644
--- a/lib/paperclip/schema.rb
+++ b/lib/paperclip/schema.rb
@@ -38,8 +38,7 @@ def remove_attachment(table_name, *attachment_names)
         options = attachment_names.extract_options!
 
         attachment_names.each do |attachment_name|
-          COLUMNS.each_pair do |column_name, column_type|
-            column_options = options.merge(options[column_name.to_sym] || {})
+          COLUMNS.keys.each do |column_name|
             remove_column(table_name, "#{attachment_name}_#{column_name}")
           end
         end
diff --git a/lib/paperclip/storage/s3.rb b/lib/paperclip/storage/s3.rb
index 50caf1b29..bb8772233 100644
--- a/lib/paperclip/storage/s3.rb
+++ b/lib/paperclip/storage/s3.rb
@@ -41,7 +41,7 @@ module Storage
     # * +s3_permissions+: This is a String that should be one of the "canned" access
     #   policies that S3 provides (more information can be found here:
     #   http://docs.aws.amazon.com/AmazonS3/latest/dev/ACLOverview.html)
-    #   The default for Paperclip is :public_read (aws-sdk v1) / public-read (aws-sdk v2).
+    #   The default for Paperclip is public-read.
     #
     #   You can set permission on a per style bases by doing the following:
     #     :s3_permissions => {
@@ -112,22 +112,23 @@ module Storage
     #     :s3_storage_class => :reduced_redundancy
 
     module S3
+      SEMAPHORE = Mutex.new
+
       def self.extended base
-        unless defined?(AWS_CLASS)
-          begin
-            require 'aws-sdk'
-            const_set('AWS_CLASS', defined?(::Aws) ? ::Aws : ::AWS)
-            const_set('AWS_BASE_ERROR',
-              defined?(::Aws) ? Aws::Errors::ServiceError : AWS::Errors::Base)
-            const_set('DEFAULT_PERMISSION',
-              defined?(::AWS) ? :public_read : :'public-read')
-
-          rescue LoadError => e
-            e.message << " (You may need to install the aws-sdk gem)"
-            raise e
-          end
-          if Gem::Version.new(AWS_CLASS::VERSION) >= Gem::Version.new(2) && Gem::Version.new(AWS_CLASS::VERSION) <= Gem::Version.new("2.0.33")
-            raise LoadError, "paperclip does not support aws-sdk versions 2.0.0 - 2.0.33.  Please upgrade aws-sdk to a newer version."
+        SEMAPHORE.synchronize do
+          unless defined?(AWS_CLASS)
+            begin
+              require 'aws-sdk-s3'
+              const_set('AWS_CLASS', defined?(::Aws) ? ::Aws : ::AWS)
+              const_set('AWS_BASE_ERROR',
+                defined?(::Aws) ? Aws::Errors::ServiceError : AWS::Errors::Base)
+              const_set('DEFAULT_PERMISSION',
+                defined?(::AWS) ? :public_read : :'public-read')
+
+            rescue LoadError => e
+              e.message << " (You may need to install the aws-sdk gem)"
+              raise e
+            end
           end
         end
 
@@ -182,10 +183,10 @@ def sanitize_hash(hash)
           "#{attachment.s3_protocol(style, true)}//#{attachment.s3_host_alias}/#{attachment.path(style).sub(%r{\A/}, "".freeze)}"
         end unless Paperclip::Interpolations.respond_to? :s3_alias_url
         Paperclip.interpolates(:s3_path_url) do |attachment, style|
-          "#{attachment.s3_protocol(style, true)}//#{attachment.s3_host_name}/#{attachment.bucket_name}/#{attachment.path(style).sub(%r{\A/}, "".freeze)}"
+          "#{attachment.s3_protocol(style, true)}//#{attachment.s3_host_name}/#{attachment.bucket_name(style)}/#{attachment.path(style).sub(%r{\A/}, "".freeze)}"
         end unless Paperclip::Interpolations.respond_to? :s3_path_url
         Paperclip.interpolates(:s3_domain_url) do |attachment, style|
-          "#{attachment.s3_protocol(style, true)}//#{attachment.bucket_name}.#{attachment.s3_host_name}/#{attachment.path(style).sub(%r{\A/}, "".freeze)}"
+          "#{attachment.s3_protocol(style, true)}//#{attachment.bucket_name(style)}.#{attachment.s3_host_name}/#{attachment.path(style).sub(%r{\A/}, "".freeze)}"
         end unless Paperclip::Interpolations.respond_to? :s3_domain_url
         Paperclip.interpolates(:asset_host) do |attachment, style|
           "#{attachment.path(style).sub(%r{\A/}, "".freeze)}"
@@ -194,13 +195,11 @@ def sanitize_hash(hash)
 
       def expiring_url(time = 3600, style_name = default_style)
         if path(style_name)
-          if aws_v1?
-            base_options = { :expires => time, :secure => use_secure_protocol?(style_name) }
-            s3_object(style_name).url_for(:read, base_options.merge(s3_url_options)).to_s
-          else
-            base_options = { :expires_in => time }
-            s3_object(style_name).presigned_url(:get, base_options.merge(s3_url_options)).to_s
-          end
+          base_options = { expires_in: time }
+          s3_object(style_name).presigned_url(
+            :get,
+            base_options.merge(s3_url_options),
+          ).to_s
         else
           url(style_name)
         end
@@ -217,9 +216,10 @@ def s3_host_name
         host_name || s3_credentials[:s3_host_name] || "s3.amazonaws.com".freeze
       end
 
-      def s3_region
+      def s3_region(style = :original)
         region = @options[:s3_region]
         region = region.call(self) if region.is_a?(Proc)
+        region = styles[style][:region] if styles[style] && styles[style][:region]
 
         region || s3_credentials[:s3_region]
       end
@@ -236,55 +236,42 @@ def s3_url_options
         s3_url_options
       end
 
-      def bucket_name
+      def bucket_name(style = default_style)
         @bucket = @options[:bucket] || s3_credentials[:bucket]
         @bucket = @bucket.call(self) if @bucket.respond_to?(:call)
+        @bucket = styles[style][:bucket] if styles[style] && styles[style][:bucket]
         @bucket or raise ArgumentError, "missing required :bucket option"
       end
 
-      def s3_interface
-        @s3_interface ||= begin
-          config = if aws_v1?
-            { :s3_endpoint => s3_host_name }
-          else
-            { :region => s3_region }
-          end
-
-          if using_http_proxy?
+      def s3_interface(style = default_style)
+        config = { region: s3_region(style) }
 
-            proxy_opts = { :host => http_proxy_host }
-            proxy_opts[:port] = http_proxy_port if http_proxy_port
-            if http_proxy_user
-              userinfo = http_proxy_user.to_s
-              userinfo += ":#{http_proxy_password}" if http_proxy_password
-              proxy_opts[:userinfo] = userinfo
-            end
-            config[:proxy_uri] = URI::HTTP.build(proxy_opts)
-          end
+        if using_http_proxy?
 
-          [:access_key_id, :secret_access_key, :credential_provider, :credentials].each do |opt|
-            config[opt] = s3_credentials[opt] if s3_credentials[opt]
+          proxy_opts = { :host => http_proxy_host }
+          proxy_opts[:port] = http_proxy_port if http_proxy_port
+          if http_proxy_user
+            userinfo = http_proxy_user.to_s
+            userinfo += ":#{http_proxy_password}" if http_proxy_password
+            proxy_opts[:userinfo] = userinfo
           end
+          config[:proxy_uri] = URI::HTTP.build(proxy_opts)
+        end
 
-          obtain_s3_instance_for(config.merge(@s3_options))
+        [:access_key_id, :secret_access_key, :credential_provider, :credentials].each do |opt|
+          config[opt] = s3_credentials[opt] if s3_credentials[opt]
         end
+
+        obtain_s3_instance_for(config.merge(@s3_options))
       end
 
       def obtain_s3_instance_for(options)
         instances = (Thread.current[:paperclip_s3_instances] ||= {})
-        instances[options] ||= if aws_v1?
-          AWS_CLASS::S3.new(options)
-        else
-          AWS_CLASS::S3::Resource.new(options)
-        end
+        instances[options] ||= AWS_CLASS::S3::Resource.new(options)
       end
 
-      def s3_bucket
-        @s3_bucket ||= if aws_v1?
-          s3_interface.buckets[bucket_name]
-        else
-          s3_interface.bucket(bucket_name)
-        end
+      def s3_bucket(style = default_style)
+        s3_interface(style).bucket(bucket_name(style))
       end
 
       def style_name_as_path(style_name)
@@ -292,11 +279,7 @@ def style_name_as_path(style_name)
       end
 
       def s3_object style_name = default_style
-        if aws_v1?
-          s3_bucket.objects[style_name_as_path(style_name)]
-        else
-          s3_bucket.object(style_name_as_path(style_name))
-        end
+        s3_bucket(style_name).object style_name_as_path(style_name)
       end
 
       def using_http_proxy?
@@ -366,24 +349,18 @@ def s3_protocol(style = default_style, with_colon = false)
         end
       end
 
-      def create_bucket
-        if aws_v1?
-          s3_interface.buckets.create(bucket_name)
-        else
-          s3_interface.bucket(bucket_name).create
-        end
+      def create_bucket(style_name)
+        s3_interface(style_name).bucket(bucket_name(style_name)).create
       end
 
       def flush_writes #:nodoc:
-        @queued_for_write.each do |style, file|
+        @queued_for_write.peach(3) do |style, file|
         retries = 0
           begin
             log("saving #{path(style)}")
-            acl = @s3_permissions[style] || @s3_permissions[:default]
-            acl = acl.call(self, style) if acl.respond_to?(:call)
             write_options = {
               :content_type => file.content_type,
-              :acl => acl
+              :acl => s3_permissions(style)
             }
 
             # add storage class for this style if defined
@@ -404,13 +381,10 @@ def flush_writes #:nodoc:
             write_options[:metadata] = @s3_metadata unless @s3_metadata.empty?
             write_options.merge!(@s3_headers)
 
-            if aws_v1?
-              s3_object(style).write(file, write_options)
-            else
-              s3_object(style).upload_file(file.path, write_options)
-            end
+            puts "******* #{s3_object.inspect}"
+            s3_object(style).upload_file(file.path, write_options)
           rescue AWS_CLASS::S3::Errors::NoSuchBucket
-            create_bucket
+            create_bucket(style)
             retry
           rescue AWS_CLASS::S3::Errors::SlowDown
             retries += 1
@@ -431,14 +405,11 @@ def flush_writes #:nodoc:
       end
 
       def flush_deletes #:nodoc:
+        # TODO figure out style from path
         @queued_for_delete.each do |path|
           begin
             log("deleting #{path}")
-            if aws_v1?
-              s3_bucket.objects[path.sub(%r{\A/},'')]
-            else
-              s3_bucket.object(path.sub(%r{\A/},''))
-            end.delete
+            s3_bucket.object(path.sub(%r{\A/}, "")).delete
           rescue AWS_BASE_ERROR => e
             # Ignore this.
           end
@@ -449,7 +420,7 @@ def flush_deletes #:nodoc:
       def copy_to_local_file(style, local_dest_path)
         log("copying #{path(style)} to local file #{local_dest_path}")
         ::File.open(local_dest_path, 'wb') do |local_file|
-          s3_object(style).send(aws_v1? ? :read : :get) do |chunk|
+          s3_object(style).get do |chunk|
             local_file.write(chunk)
           end
         end
@@ -460,10 +431,6 @@ def copy_to_local_file(style, local_dest_path)
 
       private
 
-      def aws_v1?
-        Gem::Version.new(AWS_CLASS::VERSION) < Gem::Version.new(2)
-      end
-
       def find_credentials creds
         case creds
         when File
diff --git a/lib/paperclip/url_generator.rb b/lib/paperclip/url_generator.rb
index bed60f2ab..2b528a8ee 100644
--- a/lib/paperclip/url_generator.rb
+++ b/lib/paperclip/url_generator.rb
@@ -2,6 +2,13 @@
 
 module Paperclip
   class UrlGenerator
+    class << self
+      def encoder
+        @encoder ||= URI::RFC2396_Parser.new
+      end
+      delegate :escape, :unescape, to: :encoder
+    end
+
     def initialize(attachment, attachment_options)
       @attachment = attachment
       @attachment_options = attachment_options
@@ -61,7 +68,7 @@ def escape_url(url)
       if url.respond_to?(:escape)
         url.escape
       else
-        URI.escape(url).gsub(escape_regex){|m| "%#{m.ord.to_s(16).upcase}" }
+        self.class.escape(url).gsub(escape_regex){|m| "%#{m.ord.to_s(16).upcase}" }
       end
     end
 
diff --git a/lib/paperclip/validators/media_type_spoof_detection_validator.rb b/lib/paperclip/validators/media_type_spoof_detection_validator.rb
index d3699acc1..4bbe9dff9 100644
--- a/lib/paperclip/validators/media_type_spoof_detection_validator.rb
+++ b/lib/paperclip/validators/media_type_spoof_detection_validator.rb
@@ -8,6 +8,7 @@ def validate_each(record, attribute, value)
         if Paperclip::MediaTypeSpoofDetector.using(adapter, value.original_filename, value.content_type).spoofed?
           record.errors.add(attribute, :spoofed_media_type)
         end
+        adapter.tempfile.close(true) if adapter.tempfile
       end
     end
 
diff --git a/paperclip.gemspec b/paperclip.gemspec
index da32719cc..f330af1dc 100644
--- a/paperclip.gemspec
+++ b/paperclip.gemspec
@@ -17,7 +17,7 @@ Gem::Specification.new do |s|
   s.executables   = `git ls-files -- bin/*`.split("\n").map{ |f| File.basename(f) }
   s.require_paths = ["lib"]
 
-  if File.exists?('UPGRADING')
+  if File.exist?('UPGRADING')
     s.post_install_message = File.read("UPGRADING")
   end
 
@@ -28,7 +28,7 @@ Gem::Specification.new do |s|
   s.add_dependency('activesupport', '>= 3.2.0')
   s.add_dependency('cocaine', '~> 0.5.5')
   s.add_dependency('mime-types')
-  s.add_dependency('mimemagic', '0.3.0')
+  s.add_dependency('mimemagic', '~> 0.3.0')
 
   s.add_development_dependency('activerecord', '>= 3.2.0')
   s.add_development_dependency('shoulda')
diff --git a/spec/paperclip/attachment_spec.rb b/spec/paperclip/attachment_spec.rb
index 7dbf79fed..ac8015c5a 100644
--- a/spec/paperclip/attachment_spec.rb
+++ b/spec/paperclip/attachment_spec.rb
@@ -1374,6 +1374,12 @@ def call(filename)
     end
 
     it "does not calculate fingerprint" do
+      Digest::MD5.stubs(:file)
+      @dummy.avatar = @file
+      expect(Digest::MD5).to have_received(:file).never
+    end
+
+    it "does not assign fingerprint" do
       @dummy.avatar = @file
       assert_nil @dummy.avatar.fingerprint
     end
diff --git a/spec/paperclip/integration_spec.rb b/spec/paperclip/integration_spec.rb
index e820e494d..b4118f272 100644
--- a/spec/paperclip/integration_spec.rb
+++ b/spec/paperclip/integration_spec.rb
@@ -3,14 +3,25 @@
 require 'open-uri'
 
 describe 'Paperclip' do
+  around do |example|
+    files, files2 = nil, nil
+    files = ObjectSpace.each_object(Tempfile).select{|x| x.path && File.file?(x.path)}
+    example.run
+    files2 = ObjectSpace.each_object(Tempfile).select{|x| x.path && File.file?(x.path)}
+    diff = files2-files
+    expect(diff).to eq([]), "Leaked tempfiles: #{diff.inspect}"
+  end
+
   context "Many models at once" do
     before do
       rebuild_model
       @file = File.new(fixture_file("5k.png"), 'rb')
       # Deals with `Too many open files` error
-      Dummy.import 100.times.map { Dummy.new avatar: @file }
-      Dummy.import 100.times.map { Dummy.new avatar: @file }
-      Dummy.import 100.times.map { Dummy.new avatar: @file }
+      dummies = 300.times.map { Dummy.new avatar: @file }
+      Dummy.import dummies
+      # save attachment instances to run after hooks including tempfile cleanup
+      # since activerecord-import does not use our usually hooked-in hooks (such as after_save)
+      dummies.each{|d| d.avatar.save }
     end
 
     after { @file.close }
@@ -159,7 +170,11 @@
       assert_not_equal File.size(@file.path), @dummy.avatar.size
     end
 
-    after { @file.close }
+    after do
+      @file.close
+      # save attachment instance to run after hooks (including tempfile cleanup)
+      @dummy.avatar.save
+    end
   end
 
   context "A model with attachments scoped under an id" do
@@ -347,6 +362,8 @@
     it "is not ok with bad files" do
       @dummy.avatar = @bad_file
       assert ! @dummy.valid?
+      # save attachment instance to run after hooks (including tempfile cleanup)
+      @dummy.avatar.save
     end
 
     it "knows the difference between good files, bad files, and not files when validating" do
@@ -354,8 +371,13 @@
       @d2 = Dummy.find(@dummy.id)
       @d2.avatar = @file
       assert  @d2.valid?, @d2.errors.full_messages.inspect
+      # save attachment instance to run after hooks (including tempfile cleanup)
+      @d2.avatar.save
+
       @d2.avatar = @bad_file
       assert ! @d2.valid?
+      # save attachment instance to run after hooks (including tempfile cleanup)
+      @d2.avatar.save
     end
 
     it "is able to reload without saving and not have the file disappear" do
diff --git a/spec/paperclip/paperclip_spec.rb b/spec/paperclip/paperclip_spec.rb
index c47dfdbc6..6d87b5b4f 100644
--- a/spec/paperclip/paperclip_spec.rb
+++ b/spec/paperclip/paperclip_spec.rb
@@ -123,33 +123,6 @@ class ::Four; end
       end
     end
 
-    if using_protected_attributes?
-      context "that is attr_protected" do
-        before do
-          Dummy.class_eval do
-            attr_protected :avatar
-          end
-          @dummy = Dummy.new
-        end
-
-        it "does not assign the avatar on mass-set" do
-          @dummy.attributes = { other: "I'm set!",
-                                avatar: @file }
-
-          assert_equal "I'm set!", @dummy.other
-          assert ! @dummy.avatar?
-        end
-
-        it "allows assigment on normal set" do
-          @dummy.other  = "I'm set!"
-          @dummy.avatar = @file
-
-          assert_equal "I'm set!", @dummy.other
-          assert @dummy.avatar?
-        end
-      end
-    end
-
     context "with a subclass" do
       before do
         class ::SubDummy < Dummy; end
diff --git a/spec/paperclip/storage/s3_spec.rb b/spec/paperclip/storage/s3_spec.rb
index c361bfc35..82fbf612e 100644
--- a/spec/paperclip/storage/s3_spec.rb
+++ b/spec/paperclip/storage/s3_spec.rb
@@ -1,5 +1,5 @@
 require 'spec_helper'
-require 'aws-sdk'
+require 'aws-sdk-s3'
 
 describe Paperclip::Storage::S3 do
   before do
@@ -14,6 +14,19 @@ def aws2_add_region
     defined?(::Aws) ? { s3_region: 'us-east-1' } : {}
   end
 
+  context "multithreaded initialization" do
+    it "should not fail on missing constants" do
+      10.times.map do |i|
+        Thread.new do
+          ActiveRecord::Base.connection_pool.with_connection do |_|
+            rebuild_model (aws2_add_region).merge storage: :s3
+            Dummy.new.avatar
+          end
+        end
+      end.map{|t| t.join}
+    end
+  end
+
   context "Parsing S3 credentials" do
     before do
       @proxy_settings = {host: "127.0.0.1", port: 8888, user: "foo", password: "bar"}
diff --git a/spec/spec_helper.rb b/spec/spec_helper.rb
index 887b432ad..036770123 100644
--- a/spec/spec_helper.rb
+++ b/spec/spec_helper.rb
@@ -37,7 +37,6 @@
   config.include ModelReconstruction
   config.include TestData
   config.extend VersionHelper
-  config.extend RailsHelpers::ClassMethods
   config.mock_framework = :mocha
   config.before(:all) do
     rebuild_model
diff --git a/spec/support/rails_helpers.rb b/spec/support/rails_helpers.rb
deleted file mode 100644
index fb45bff1f..000000000
--- a/spec/support/rails_helpers.rb
+++ /dev/null
@@ -1,7 +0,0 @@
-module RailsHelpers
-  module ClassMethods
-    def using_protected_attributes?
-      ActiveRecord::VERSION::MAJOR < 4
-    end
-  end
-end