Mirror: explicit primary service and list of mirrors

Pass separate primary service and list of mirrors rather than treating
the first of the services list as the primary. Nice fit for keyword args,
and something we've long wanted in the equivalent Basecamp file repository.

Upload returns the results of the underlying service uploads rather than
the io.rewind result. Rewind before uploading rather than afterward, and
demonstrate that behavior with a test.

Test that more than one mirror works.

1 files changed, 9 insertions, 10 deletions

diff --git a/lib/active_storage/service/mirror_service.rb b/lib/active_storage/service/mirror_service.rb
index 1ec0930e6c..7ec166aace 100644
--- a/lib/active_storage/service/mirror_service.rb
+++ b/lib/active_storage/service/mirror_service.rb
@@ -1,18 +1,17 @@
 require "active_support/core_ext/module/delegation"
 
 class ActiveStorage::Service::MirrorService < ActiveStorage::Service
-  attr_reader :services
+  attr_reader :primary, :mirrors
 
-  delegate :download, :exist?, :url, to: :primary_service
+  delegate :download, :exist?, :url, to: :primary
 
-  def initialize(services:)
-    @services = services
+  def initialize(primary:, mirrors:)
+    @primary, @mirrors = primary, mirrors
   end
 
   def upload(key, io, checksum: nil)
-    services.collect do |service|
-      service.upload key, io, checksum: checksum
-      io.rewind
+    each_service.collect do |service|
+      service.upload key, io.tap(&:rewind), checksum: checksum
     end
   end
 
@@ -21,13 +20,13 @@ class ActiveStorage::Service::MirrorService < ActiveStorage::Service
   end
 
   private
-    def primary_service
-      services.first
+    def each_service(&block)
+      [ primary, *mirrors ].each(&block)
     end
 
     def perform_across_services(method, *args)
       # FIXME: Convert to be threaded
-      services.collect do |service|
+      each_service.collect do |service|
         service.public_send method, *args
       end
     end