4 files changed, 24 insertions, 21 deletions
diff --git a/activestorage/lib/active_storage/analyzer.rb b/activestorage/lib/active_storage/analyzer.rb
index caa25418a5..26414ffbc2 100644
--- a/activestorage/lib/active_storage/analyzer.rb
+++ b/activestorage/lib/active_storage/analyzer.rb
@@ -24,14 +24,14 @@ module ActiveStorage
     private
       # Downloads the blob to a tempfile on disk. Yields the tempfile.
       def download_blob_to_tempfile(&block) #:doc:
-        blob.open tempdir: tempdir, &block
+        blob.open tmpdir: tmpdir, &block
       end
 
       def logger #:doc:
         ActiveStorage.logger
       end
 
-      def tempdir #:doc:
+      def tmpdir #:doc:
         Dir.tmpdir
       end
   end
diff --git a/activestorage/lib/active_storage/downloader.rb b/activestorage/lib/active_storage/downloader.rb
index 87be6efb05..4d7e832af5 100644
--- a/activestorage/lib/active_storage/downloader.rb
+++ b/activestorage/lib/active_storage/downloader.rb
@@ -2,24 +2,23 @@
 
 module ActiveStorage
   class Downloader #:nodoc:
-    def initialize(blob, tempdir: nil)
-      @blob    = blob
-      @tempdir = tempdir
+    attr_reader :service
+
+    def initialize(service)
+      @service = service
     end
 
-    def download_blob_to_tempfile
-      open_tempfile do |file|
-        download_blob_to file
-        verify_integrity_of file
+    def open(key, checksum:, name: "ActiveStorage-", tmpdir: nil)
+      open_tempfile(name, tmpdir) do |file|
+        download key, file
+        verify_integrity_of file, checksum: checksum
         yield file
       end
     end
 
     private
-      attr_reader :blob, :tempdir
-
-      def open_tempfile
-        file = Tempfile.open([ "ActiveStorage-#{blob.id}-", blob.filename.extension_with_delimiter ], tempdir)
+      def open_tempfile(name, tmpdir = nil)
+        file = Tempfile.open(name, tmpdir)
 
         begin
           yield file
@@ -28,15 +27,15 @@ module ActiveStorage
         end
       end
 
-      def download_blob_to(file)
+      def download(key, file)
         file.binmode
-        blob.download { |chunk| file.write(chunk) }
+        service.download(key) { |chunk| file.write(chunk) }
         file.flush
         file.rewind
       end
 
-      def verify_integrity_of(file)
-        unless Digest::MD5.file(file).base64digest == blob.checksum
+      def verify_integrity_of(file, checksum:)
+        unless Digest::MD5.file(file).base64digest == checksum
           raise ActiveStorage::IntegrityError
         end
       end
diff --git a/activestorage/lib/active_storage/previewer.rb b/activestorage/lib/active_storage/previewer.rb
index 95a041fd16..af6bcadd4c 100644
--- a/activestorage/lib/active_storage/previewer.rb
+++ b/activestorage/lib/active_storage/previewer.rb
@@ -26,7 +26,7 @@ module ActiveStorage
     private
       # Downloads the blob to a tempfile on disk. Yields the tempfile.
       def download_blob_to_tempfile(&block) #:doc:
-        blob.open tempdir: tempdir, &block
+        blob.open tmpdir: tmpdir, &block
       end
 
       # Executes a system command, capturing its binary output in a tempfile. Yields the tempfile.
@@ -42,7 +42,7 @@ module ActiveStorage
       #     end
       #   end
       #
-      # The output tempfile is opened in the directory returned by #tempdir.
+      # The output tempfile is opened in the directory returned by #tmpdir.
       def draw(*argv) #:doc:
         open_tempfile do |file|
           instrument :preview, key: blob.key do
@@ -54,7 +54,7 @@ module ActiveStorage
       end
 
       def open_tempfile
-        tempfile = Tempfile.open("ActiveStorage-", tempdir)
+        tempfile = Tempfile.open("ActiveStorage-", tmpdir)
 
         begin
           yield tempfile
@@ -77,7 +77,7 @@ module ActiveStorage
         ActiveStorage.logger
       end
 
-      def tempdir #:doc:
+      def tmpdir #:doc:
         Dir.tmpdir
       end
   end
diff --git a/activestorage/lib/active_storage/service.rb b/activestorage/lib/active_storage/service.rb
index c18fccbb1d..aac1e62e7f 100644
--- a/activestorage/lib/active_storage/service.rb
+++ b/activestorage/lib/active_storage/service.rb
@@ -82,6 +82,10 @@ module ActiveStorage
       raise NotImplementedError
     end
 
+    def open(*args, &block)
+      ActiveStorage::Downloader.new(self).open(*args, &block)
+    end
+
     # Delete the file at the +key+.
     def delete(key)
       raise NotImplementedError