1 files changed, 38 insertions, 0 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
new file mode 100644
index 0000000000..244a2e439b
--- /dev/null
+++ b/actionmailbox/app/models/action_mailbox/inbound_email/message_id.rb
@@ -0,0 +1,38 @@
+# frozen_string_literal: true
+
+# The `Message-ID` as specified by rfc822 is supposed to be a unique identifier for that individual email.
+# That makes it an ideal tracking token for debugging and forensics, just like `X-Request-Id` does for
+# web request.
+#
+# If an inbound email does not, against the rfc822 mandate, specify a Message-ID, one will be generated
+# using the approach from `Mail::MessageIdField`.
+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! message_id: extract_message_id(source), **options do |inbound_email|
+        inbound_email.raw_email.attach io: StringIO.new(source), filename: "message.eml", content_type: "message/rfc822"
+      end
+    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}"
+      end
+    end
+end