Add CarrierWave::MagicMimeTypes mixin

This module extracts the file content-type using ruby-filemagic gem
for more accurate results

lib/carrierwave/processing.rb

@@ -1,3 +1,4 @@
 require "carrierwave/processing/rmagick"
 require "carrierwave/processing/mini_magick"
 require "carrierwave/processing/mime_types"
+require "carrierwave/processing/magic_mime_types"

lib/carrierwave/processing/magic_mime_types.rb

@@ -0,0 +1,71 @@
+# encoding: utf-8
+
+module CarrierWave
+  ##
+  # This module simplifies the use of ruby-filemagic gem to intelligently
+  # and correctly guess and set the content-type of a file. If you want 
+  # to use this, you'll need to require this file:
+  #
+  #    require 'carrierwave/processing/magic_mime_types'
+  #
+  # And then include it in your uploader:
+  #
+  #   class MyUploader < CarrierWave::Uploader::Base
+  #     include CarrierWave::MagicMimeTypes
+  #   end
+  #
+  # You can use the provided helper:
+  #
+  #   class MyUploader < CarrierWave::Uploader::Base
+  #     include CarrierWave::MagicMimeTypes
+  #
+  #     process :set_content_type
+  #   end
+  module MagicMimeTypes
+    extend ActiveSupport::Concern
+
+    included do
+      begin
+        require "filemagic"
+      rescue LoadError => e
+        e.message << " (You may need to install the ruby-filemagic gem)"
+        raise e
+      end
+    end
+
+    module ClassMethods
+      def set_content_type(override=false)
+        process :set_content_type => override
+      end
+    end
+
+    ##
+    # Changes the file content_type using the ruby-filemagic gem
+    #
+    # === Parameters
+    #
+    # [override (Boolean)] wheter or not to override the file's content_type
+    #                      if it is already set, false by default
+    def set_content_type(override=false)
+      if override || file.content_type.blank?
+        File.open(file.path) do |fd|
+          data = fd.read(1024) || ""
+          new_content_type = filemagic.buffer(data)
+          if file.respond_to?(:content_type=)
+            file.content_type = new_content_type
+          else
+            file.instance_variable_set(:@content_type, new_content_type)
+          end
+        end
+      end
+    end
+
+    ##
+    # FileMagic object with the MAGIC_MIME_TYPE flag set
+    #
+    # @return [FileMagic] a filemagic object
+    def filemagic
+      @filemagic ||= FileMagic.new(FileMagic::MAGIC_MIME_TYPE)
+    end
+  end
+end

spec/processing/magic_mime_types_spec.rb

@@ -0,0 +1,49 @@
+# encoding: utf-8
+
+require 'spec_helper'
+
+describe CarrierWave::MagicMimeTypes do
+
+  before do
+    @klass = Class.new(CarrierWave::Uploader::Base) do
+      attr_accessor :content_type
+      include CarrierWave::MagicMimeTypes
+    end
+    @instance = @klass.new
+    FileUtils.cp(file_path('ruby.gif'), file_path('ruby_copy.gif'))
+    @instance.stub(:original_filename).and_return file_path('ruby_copy.gif')
+    @instance.stub(:file).and_return CarrierWave::SanitizedFile.new(file_path('ruby_copy.gif'))
+    @file = @instance.file
+  end
+
+  after do
+    FileUtils.rm(file_path('ruby_copy.gif'))
+  end
+
+  describe "#set_content_type" do
+    it "does not set the content_type if already set" do
+      @instance.file.content_type = 'image/jpeg'
+      @instance.file.should_not_receive(:content_type=)
+      @instance.set_content_type
+    end
+
+    it "sets content_type if content_type is nil" do
+      pending
+      @instance.file.content_type = nil
+      @instance.file.should_receive(:content_type=).with('image/png')
+      @instance.set_content_type
+    end
+
+    it "sets content_type if content_type is blank" do
+      @instance.file.content_type = ''
+      @instance.file.should_receive(:content_type=).with('image/png')
+      @instance.set_content_type
+    end
+
+    it "sets content_type if override is true" do
+      @instance.file.content_type = 'image/png'
+      @instance.file.should_receive(:content_type=).with('image/png')
+      @instance.set_content_type(true)
+    end
+  end
+end