Extract `BaseDownloader` and use it on other classes

`BaseDownloader` is now the base class for `FileDownloader`,
`JobArtifactDownloader`, and `LfsDownloader`

ee/lib/gitlab/geo/replication/base_downloader.rb

+# frozen_string_literal: true
+
+module Gitlab
+  module Geo
+    module Replication
+      class BaseDownloader
+        attr_reader :object_type, :object_db_id
+
+        def initialize(object_type, object_db_id)
+          @object_type = object_type
+          @object_db_id = object_db_id
+        end
+
+        class Result
+          attr_reader :success, :bytes_downloaded, :primary_missing_file, :failed_before_transfer
+
+          def self.from_transfer_result(transfer_result)
+            Result.new(success: transfer_result.success,
+                       primary_missing_file: transfer_result.primary_missing_file,
+                       bytes_downloaded: transfer_result.bytes_downloaded)
+          end
+
+          def initialize(success:, bytes_downloaded:, primary_missing_file: false, failed_before_transfer: false)
+            @success = success
+            @bytes_downloaded = bytes_downloaded
+            @primary_missing_file = primary_missing_file
+            @failed_before_transfer = failed_before_transfer
+          end
+        end
+
+        private
+
+        def fail_before_transfer
+          Result.new(success: false, bytes_downloaded: 0, failed_before_transfer: true)
+        end
+
+        def missing_on_primary
+          Result.new(success: true, bytes_downloaded: 0, primary_missing_file: true)
+        end
+      end
+    end
+  end
+end

ee/lib/gitlab/geo/replication/file_downloader.rb

@@ -8,23 +8,13 @@ module Gitlab
       #   * Requesting and downloading the Upload's file from the primary
       #   * Returning a detailed Result
       #
-      # TODO: Rearrange things so this class not inherited by JobArtifactDownloader and LfsDownloader
-      # Maybe rename it so it doesn't seem generic. It only works with Upload records.
-      class FileDownloader
-        attr_reader :object_type, :object_db_id
-
-        def initialize(object_type, object_db_id)
-          @object_type = object_type
-          @object_db_id = object_db_id
-        end
-
+      class FileDownloader < BaseDownloader
         # Executes the actual file download
         #
         # Subclasses should return the number of bytes downloaded,
         # or nil or -1 if a failure occurred.
-        # rubocop: disable CodeReuse/ActiveRecord
         def execute
-          upload = Upload.find_by(id: object_db_id)
+          upload = find_resource
           return fail_before_transfer unless upload.present?
           return missing_on_primary if upload.model.nil?
 
@@ -32,34 +22,15 @@ module Gitlab
           Result.from_transfer_result(transfer.download_from_primary)
         end
 
-        # rubocop: enable CodeReuse/ActiveRecord
-
-        class Result
-          attr_reader :success, :bytes_downloaded, :primary_missing_file, :failed_before_transfer
-
-          def self.from_transfer_result(transfer_result)
-            Result.new(success: transfer_result.success,
-                       primary_missing_file: transfer_result.primary_missing_file,
-                       bytes_downloaded: transfer_result.bytes_downloaded)
-          end
-
-          def initialize(success:, bytes_downloaded:, primary_missing_file: false, failed_before_transfer: false)
-            @success = success
-            @bytes_downloaded = bytes_downloaded
-            @primary_missing_file = primary_missing_file
-            @failed_before_transfer = failed_before_transfer
-          end
-        end
-
         private
 
-        def fail_before_transfer
-          Result.new(success: false, bytes_downloaded: 0, failed_before_transfer: true)
-        end
+        # rubocop: disable CodeReuse/ActiveRecord
 
-        def missing_on_primary
-          Result.new(success: true, bytes_downloaded: 0, primary_missing_file: true)
+        def find_resource
+          Upload.find_by(id: object_db_id)
         end
+
+        # rubocop: enable CodeReuse/ActiveRecord
       end
     end
   end

ee/lib/gitlab/geo/replication/job_artifact_downloader.rb

@@ -8,16 +8,23 @@ module Gitlab
       #   * Requesting and downloading the JobArtifact's file from the primary
       #   * Returning a detailed Result
       #
-      # TODO: Rearrange things so this class does not inherit FileDownloader
-      class JobArtifactDownloader < FileDownloader
-        # rubocop: disable CodeReuse/ActiveRecord
+      class JobArtifactDownloader < BaseDownloader
         def execute
-          job_artifact = ::Ci::JobArtifact.find_by(id: object_db_id)
+          job_artifact = find_resource
           return fail_before_transfer unless job_artifact.present?
 
           transfer = ::Gitlab::Geo::Replication::JobArtifactTransfer.new(job_artifact)
           Result.from_transfer_result(transfer.download_from_primary)
         end
+
+        private
+
+        # rubocop: disable CodeReuse/ActiveRecord
+
+        def find_resource
+          ::Ci::JobArtifact.find_by(id: object_db_id)
+        end
+
         # rubocop: enable CodeReuse/ActiveRecord
       end
     end

ee/lib/gitlab/geo/replication/lfs_downloader.rb

@@ -8,16 +8,23 @@ module Gitlab
       #   * Requesting and downloading the LfsObject's file from the primary
       #   * Returning a detailed Result
       #
-      # TODO: Rearrange things so this class does not inherit FileDownloader
-      class LfsDownloader < FileDownloader
-        # rubocop: disable CodeReuse/ActiveRecord
+      class LfsDownloader < BaseDownloader
         def execute
-          lfs_object = LfsObject.find_by(id: object_db_id)
+          lfs_object = find_resource
           return fail_before_transfer unless lfs_object.present?
 
           transfer = ::Gitlab::Geo::Replication::LfsTransfer.new(lfs_object)
           Result.from_transfer_result(transfer.download_from_primary)
         end
+
+        private
+
+        # rubocop: disable CodeReuse/ActiveRecord
+
+        def find_resource
+          LfsObject.find_by(id: object_db_id)
+        end
+
         # rubocop: enable CodeReuse/ActiveRecord
       end
     end