Expose chunked downloads

lib/active_storage/blob.rb

@@ -56,8 +56,8 @@ class ActiveStorage::Blob < ActiveRecord::Base
     service.upload(key, io, checksum: checksum)
   end
 
-  def download
-    service.download key
+  def download(&block)
+    service.download key, &block
   end
 
 

lib/active_storage/service/disk_service.rb

@@ -20,8 +20,8 @@ class ActiveStorage::Service::DiskService < ActiveStorage::Service
   def download(key)
     if block_given?
       instrument :streaming_download, key do
-        File.open(path_for(key)) do |file|
-          while data = file.binread(64.kilobytes)
+        File.open(path_for(key), 'rb') do |file|
+          while data = file.read(64.kilobytes)
             yield data
           end
         end
@@ -55,7 +55,7 @@ class ActiveStorage::Service::DiskService < ActiveStorage::Service
     instrument :url, key do |payload|
       verified_key_with_expiration = ActiveStorage::VerifiedKeyWithExpiration.encode(key, expires_in: expires_in)
 
-      generated_url = 
+      generated_url =
         if defined?(Rails) && defined?(Rails.application)
           Rails.application.routes.url_helpers.rails_disk_blob_path(verified_key_with_expiration, disposition: disposition, filename: filename)
         else
@@ -63,7 +63,7 @@ class ActiveStorage::Service::DiskService < ActiveStorage::Service
         end
 
       payload[:url] = generated_url
-      
+
       generated_url
     end
   end

test/blob_test.rb

@@ -12,6 +12,19 @@ class ActiveStorage::BlobTest < ActiveSupport::TestCase
     assert_equal Digest::MD5.base64digest(data), blob.checksum
   end
 
+  test "download yields chunks" do
+    blob   = create_blob data: 'a' * 75.kilobytes
+    chunks = []
+
+    blob.download do |chunk|
+      chunks << chunk
+    end
+
+    assert_equal 2, chunks.size
+    assert_equal 'a' * 64.kilobytes, chunks.first
+    assert_equal 'a' * 11.kilobytes, chunks.second
+  end
+
   test "urls expiring in 5 minutes" do
     blob = create_blob