1 files changed, 44 insertions, 0 deletions
diff --git a/activestorage/lib/active_storage/downloader.rb b/activestorage/lib/active_storage/downloader.rb
new file mode 100644
index 0000000000..87be6efb05
--- /dev/null
+++ b/activestorage/lib/active_storage/downloader.rb
@@ -0,0 +1,44 @@
+# frozen_string_literal: true
+
+module ActiveStorage
+  class Downloader #:nodoc:
+    def initialize(blob, tempdir: nil)
+      @blob    = blob
+      @tempdir = tempdir
+    end
+
+    def download_blob_to_tempfile
+      open_tempfile do |file|
+        download_blob_to file
+        verify_integrity_of file
+        yield file
+      end
+    end
+
+    private
+      attr_reader :blob, :tempdir
+
+      def open_tempfile
+        file = Tempfile.open([ "ActiveStorage-#{blob.id}-", blob.filename.extension_with_delimiter ], tempdir)
+
+        begin
+          yield file
+        ensure
+          file.close!
+        end
+      end
+
+      def download_blob_to(file)
+        file.binmode
+        blob.download { |chunk| file.write(chunk) }
+        file.flush
+        file.rewind
+      end
+
+      def verify_integrity_of(file)
+        unless Digest::MD5.file(file).base64digest == blob.checksum
+          raise ActiveStorage::IntegrityError
+        end
+      end
+  end
+end