Allow UploadedFileAdapter to force the use of `file`

* Based on rfc2822's commit ed05dc6b85f52ad88a83bc18e1986f3b75176740.

lib/paperclip.rb

@@ -40,6 +40,7 @@ require 'paperclip/attachment'
 require 'paperclip/attachment_options'
 require 'paperclip/storage'
 require 'paperclip/callbacks'
+require 'paperclip/file_command_content_type_detector'
 require 'paperclip/content_type_detector'
 require 'paperclip/glue'
 require 'paperclip/errors'

lib/paperclip/content_type_detector.rb

@@ -49,18 +49,7 @@ module Paperclip
     end
 
     def type_from_file_command
-      type = begin
-        # On BSDs, `file` doesn't give a result code of 1 if the file doesn't exist.
-        Paperclip.run("file", "-b --mime :file", :file => @filename)
-      rescue Cocaine::CommandLineError => e
-        Paperclip.log("Error while determining content type: #{e}")
-        SENSIBLE_DEFAULT
-      end
-
-      if type.nil? || type.match(/\(.*?\)/)
-        type = SENSIBLE_DEFAULT
-      end
-      type.split(/[:;\s]+/)[0]
+      FileCommandContentTypeDetector.new(@filename).detect
     end
 
   end

lib/paperclip/file_command_content_type_detector.rb

+module Paperclip
+  class FileCommandContentTypeDetector
+    SENSIBLE_DEFAULT = "application/octet-stream"
+
+    def initialize(filename)
+      @filename = filename
+    end
+
+    def detect
+      type_from_file_command
+    end
+
+    private
+
+    def type_from_file_command
+      type = begin
+        # On BSDs, `file` doesn't give a result code of 1 if the file doesn't exist.
+        Paperclip.run("file", "-b --mime :file", :file => @filename)
+      rescue Cocaine::CommandLineError => e
+        Paperclip.log("Error while determining content type: #{e}")
+        SENSIBLE_DEFAULT
+      end
+
+      if type.nil? || type.match(/\(.*?\)/)
+        type = SENSIBLE_DEFAULT
+      end
+      type.split(/[:;\s]+/)[0]
+    end
+
+  end
+end
+

lib/paperclip/io_adapters/uploaded_file_adapter.rb

@@ -11,13 +11,29 @@ module Paperclip
       end
     end
 
+    class << self
+      attr_accessor :content_type_detector
+    end
+
     private
 
     def cache_current_values
       @original_filename = @target.original_filename
-      @content_type = @target.content_type.to_s.strip
+      @content_type = determine_content_type
       @size = File.size(@target.path)
     end
+
+    def content_type_detector
+      self.class.content_type_detector
+    end
+
+    def determine_content_type
+      content_type = @target.content_type.to_s.strip
+      if content_type_detector
+        content_type = content_type_detector.new(@target.path).detect
+      end
+      content_type
+    end
   end
 end
 

test/content_type_detector_test.rb

@@ -37,10 +37,4 @@ class ContentTypeDetectorTest < Test::Unit::TestCase
       assert_equal "application/octet-stream", Paperclip::ContentTypeDetector.new(@filename).detect
     end
   end
-
-  should 'return a sensible default on the odd change that run returns nil' do
-    Paperclip.stubs(:run).returns(nil)
-    assert_equal "application/octet-stream",
-                 Paperclip::ContentTypeDetector.new("windows").detect
-  end
 end

test/file_command_content_type_detector_test.rb

+require './test/helper'
+
+class FileCommandContentTypeDetectorTest < Test::Unit::TestCase
+  should 'return a content type based on the content of the file' do
+    tempfile = Tempfile.new("something")
+    tempfile.write("This is a file.")
+    tempfile.rewind
+
+    assert_equal "text/plain", Paperclip::FileCommandContentTypeDetector.new(tempfile.path).detect
+  end
+
+  should 'return a sensible default when the file command is missing' do
+    Paperclip.stubs(:run).raises(Cocaine::CommandLineError.new)
+    @filename = "/path/to/something"
+    assert_equal "application/octet-stream",
+      Paperclip::FileCommandContentTypeDetector.new(@filename).detect
+  end
+
+  should 'return a sensible default on the odd chance that run returns nil' do
+    Paperclip.stubs(:run).returns(nil)
+    assert_equal "application/octet-stream",
+      Paperclip::FileCommandContentTypeDetector.new("windows").detect
+  end
+end
+

test/io_adapters/uploaded_file_adapter_test.rb

@@ -4,13 +4,15 @@ class UploadedFileAdapterTest < Test::Unit::TestCase
   context "a new instance" do
     context "with UploadedFile responding to #tempfile" do
       setup do
+        Paperclip::UploadedFileAdapter.content_type_detector = nil
+
         class UploadedFile < OpenStruct; end
         tempfile = File.new(fixture_file("5k.png"))
         tempfile.binmode
 
         @file = UploadedFile.new(
           :original_filename => "5k.png",
-          :content_type => "image/png\r",
+          :content_type => "image/x-png-by-browser\r",
           :head => "",
           :tempfile => tempfile,
           :path => tempfile.path
@@ -27,7 +29,7 @@ class UploadedFileAdapterTest < Test::Unit::TestCase
       end
 
       should "get the content type" do
-        assert_equal "image/png", @subject.content_type
+        assert_equal "image/x-png-by-browser", @subject.content_type
       end
 
       should "get the file's size" do
@@ -52,10 +54,12 @@ class UploadedFileAdapterTest < Test::Unit::TestCase
 
     context "with UploadFile responding to #path" do
       setup do
+        Paperclip::UploadedFileAdapter.content_type_detector = nil
+
         class UploadedFile < OpenStruct; end
         @file = UploadedFile.new(
           :original_filename => "5k.png",
-          :content_type => "image/png",
+          :content_type => "image/x-png-by-browser",
           :head => "",
           :path => fixture_file("5k.png")
         )
@@ -71,7 +75,7 @@ class UploadedFileAdapterTest < Test::Unit::TestCase
       end
 
       should "get the content type" do
-        assert_equal "image/png", @subject.content_type
+        assert_equal "image/x-png-by-browser", @subject.content_type
       end
 
       should "get the file's size" do
@@ -94,6 +98,26 @@ class UploadedFileAdapterTest < Test::Unit::TestCase
         assert expected.length > 0
         assert_equal expected, @subject.read
       end
+
+      context "don't trust client-given MIME type" do
+        setup do
+          Paperclip::UploadedFileAdapter.content_type_detector =
+            Paperclip::FileCommandContentTypeDetector
+
+          class UploadedFile < OpenStruct; end
+          @file = UploadedFile.new(
+            :original_filename => "5k.png",
+            :content_type => "image/x-png-by-browser",
+            :head => "",
+            :path => fixture_file("5k.png")
+          )
+          @subject = Paperclip.io_adapters.for(@file)
+        end
+
+        should "get the content type" do
+          assert_equal "image/png", @subject.content_type
+        end
+      end
     end
   end
 end