Ensure Action Mailbox processes an email only once when received multiple times

This also adds a new column, message_checksum, to the action_mailbox_inbound_emails table
for storing SHA1 digest of the email source. Additionally, it makes generating the missing
message id deterministic and adds a unique index on message_checksum and message_id to
detect duplicate emails.

1 files changed, 11 insertions, 11 deletions

diff --git a/actionmailbox/app/models/action_mailbox/inbound_email/message_id.rb b/actionmailbox/app/models/action_mailbox/inbound_email/message_id.rb
index 57b4a2445d..470b93ca20 100644
--- a/actionmailbox/app/models/action_mailbox/inbound_email/message_id.rb
+++ b/actionmailbox/app/models/action_mailbox/inbound_email/message_id.rb
@@ -9,30 +9,30 @@
 module ActionMailbox::InboundEmail::MessageId
   extend ActiveSupport::Concern
 
-  included do
-    before_save :generate_missing_message_id
-  end
-
   class_methods do
     # Create a new +InboundEmail+ from the raw +source+ of the email, which be uploaded as a Active Storage
     # attachment called +raw_email+. Before the upload, extract the Message-ID from the +source+ and set
     # it as an attribute on the new +InboundEmail+.
     def create_and_extract_message_id!(source, **options)
-      create! options.merge(message_id: extract_message_id(source)) do |inbound_email|
+      message_checksum = Digest::SHA1.hexdigest(source)
+      message_id = extract_message_id(source) || generate_missing_message_id(message_checksum)
+
+      create! options.merge(message_id: message_id, message_checksum: message_checksum) do |inbound_email|
         inbound_email.raw_email.attach io: StringIO.new(source), filename: "message.eml", content_type: "message/rfc822"
       end
+    rescue ActiveRecord::RecordNotUnique
+      nil
     end
 
     private
       def extract_message_id(source)
         Mail.from_source(source).message_id rescue nil
       end
-  end
 
-  private
-    def generate_missing_message_id
-      self.message_id ||= Mail::MessageIdField.new.message_id.tap do |message_id|
-        logger.warn "Message-ID couldn't be parsed or is missing. Generated a new Message-ID: #{message_id}"
+      def generate_missing_message_id(message_checksum)
+        Mail::MessageIdField.new("<#{message_checksum}@#{::Socket.gethostname}.mail>").message_id.tap do |message_id|
+          logger.warn "Message-ID couldn't be parsed or is missing. Generated a new Message-ID: #{message_id}"
+        end
       end
-    end
+  end
 end