Only generate repository push email once

The repository push email can be very expensive to generate, especially
with syntax-highlighted diffs. Instead of generating the email for each
recipient, generate one email object and reset the Message-Id and To
headers for each recipient. (Cloning would also be expensive in the case
of large emails, although probably not as bad as generating from
scratch.)

2 files changed, 23 insertions, 7 deletions

diff --git a/app/mailers/emails/projects.rb b/app/mailers/emails/projects.rb
index 377c2999d6c..5489283432b 100644
--- a/app/mailers/emails/projects.rb
+++ b/app/mailers/emails/projects.rb
@@ -59,9 +59,9 @@ module Emails
            subject: subject("Project was moved"))
     end
 
-    def repository_push_email(project_id, recipient, opts = {})
+    def repository_push_email(project_id, opts = {})
       @message =
-        Gitlab::Email::Message::RepositoryPush.new(self, project_id, recipient, opts)
+        Gitlab::Email::Message::RepositoryPush.new(self, project_id, opts)
 
       # used in notify layout
       @target_url = @message.target_url
@@ -72,7 +72,6 @@ module Emails
 
       mail(from:      sender(@message.author_id, @message.send_from_committer_email?),
            reply_to:  @message.reply_to,
-           to:        @message.recipient,
            subject:   @message.subject)
     end
   end
diff --git a/app/workers/emails_on_push_worker.rb b/app/workers/emails_on_push_worker.rb
index c4d8595d45d..6ebcba5f39b 100644
--- a/app/workers/emails_on_push_worker.rb
+++ b/app/workers/emails_on_push_worker.rb
@@ -1,6 +1,8 @@
 class EmailsOnPushWorker
   include Sidekiq::Worker
 
+  attr_reader :email, :skip_premailer
+
   def perform(project_id, recipients, push_data, options = {})
     options.symbolize_keys!
     options.reverse_merge!(
@@ -41,11 +43,11 @@ class EmailsOnPushWorker
       end
     end
 
-    recipients.split(" ").each do |recipient|
+    recipients.split.each do |recipient|
       begin
-        Notify.repository_push_email(
-          project_id,
+        send_email(
           recipient,
+          project_id,
           author_id:                  author_id,
           ref:                        ref,
           action:                     action,
@@ -53,14 +55,29 @@ class EmailsOnPushWorker
           reverse_compare:            reverse_compare,
           send_from_committer_email:  send_from_committer_email,
           disable_diffs:              disable_diffs
-        ).deliver_now
+        )
+
       # These are input errors and won't be corrected even if Sidekiq retries
       rescue Net::SMTPFatalError, Net::SMTPSyntaxError => e
         logger.info("Failed to send e-mail for project '#{project.name_with_namespace}' to #{recipient}: #{e}")
       end
     end
   ensure
+    @email = nil
     compare = nil
     GC.start
   end
+
+  private
+
+  def send_email(recipient, project_id, options)
+    # Generating the body of this email can be expensive, so only do it once
+    @skip_premailer ||= email.present?
+    @email ||= Notify.repository_push_email(project_id, options)
+
+    email.to = recipient
+    email.add_message_id
+    email.header[:skip_premailer] = true if skip_premailer
+    email.deliver_now
+  end
 end