FEATURE: Attach backup log as upload (#13849)

Discourse automatically sends a private message after backup or
restore finished. The private message used to contain the log inline
even when it was very long. A very long log can create issues because
the length of the post will be over the maximum allowed length of a
post. When that happens, Discourse will try to create an upload with
the logs. If that fails, it will trim the log and inline it.

spec/lib/backup_restore/backuper_spec.rb

@@ -16,4 +16,59 @@ describe BackupRestore::Backuper do
 
     expect(backuper.send(:get_parameterized_title)).to eq("coding-horror")
   end
+
+  describe '#notify_user' do
+    before do
+      freeze_time Time.zone.parse('2010-01-01 12:00')
+    end
+
+    it 'includes logs if short' do
+      SiteSetting.max_export_file_size_kb = 1
+      SiteSetting.export_authorized_extensions = "tar.gz"
+
+      silence_stdout do
+        backuper = BackupRestore::Backuper.new(Discourse.system_user.id)
+
+        expect { backuper.send(:notify_user) }
+          .to change { Topic.private_messages.count }.by(1)
+          .and change { Upload.count }.by(0)
+      end
+
+      expect(Topic.last.first_post.raw).to include("```text\n[2010-01-01 12:00:00] Notifying 'system' of the end of the backup...\n```")
+    end
+
+    it 'include upload if log is long' do
+      SiteSetting.max_post_length = 250
+
+      silence_stdout do
+        backuper = silence_stdout { BackupRestore::Backuper.new(Discourse.system_user.id) }
+
+        expect { backuper.send(:notify_user) }
+          .to change { Topic.private_messages.count }.by(1)
+          .and change { Upload.where(original_filename: "log.txt.zip").count }.by(1)
+      end
+
+      expect(Topic.last.first_post.raw).to include("[log.txt.zip|attachment]")
+    end
+
+    it 'includes trimmed logs if log is long and upload cannot be saved' do
+      SiteSetting.max_post_length = 348
+      SiteSetting.max_export_file_size_kb = 1
+      SiteSetting.export_authorized_extensions = "tar.gz"
+
+      silence_stdout do
+        backuper = BackupRestore::Backuper.new(Discourse.system_user.id)
+
+        1.upto(10).each do |i|
+          backuper.send(:log, "Line #{i}")
+        end
+
+        expect { backuper.send(:notify_user) }
+          .to change { Topic.private_messages.count }.by(1)
+          .and change { Upload.count }.by(0)
+      end
+
+      expect(Topic.last.first_post.raw).to include("```text\n...\n[2010-01-01 12:00:00] Line 10\n[2010-01-01 12:00:00] Notifying 'system' of the end of the backup...\n```")
+    end
+  end
 end