From f799b8bfb1af20275bc7bc9af1362192aa6dd699 Mon Sep 17 00:00:00 2001
From: David Taylor <david@taylorhq.com>
Date: Wed, 8 Dec 2021 11:17:20 +0000
Subject: [PATCH] FIX: Ensure MessageIdService can handle hostname changes and
 multisite (#15231)

---
 lib/email/message_id_service.rb     | 6 +++---
 spec/lib/message_id_service_spec.rb | 8 ++++++++
 2 files changed, 11 insertions(+), 3 deletions(-)

diff --git a/lib/email/message_id_service.rb b/lib/email/message_id_service.rb
index a3ba96424ae..4143d00d8de 100644
--- a/lib/email/message_id_service.rb
+++ b/lib/email/message_id_service.rb
@@ -80,11 +80,11 @@ module Email
       end
 
       def message_id_post_id_regexp
-        @message_id_post_id_regexp ||= Regexp.new "topic/\\d+/(\\d+|\\d+\.\\w+)@#{Regexp.escape(host)}"
+        Regexp.new "topic/\\d+/(\\d+|\\d+\.\\w+)@#{Regexp.escape(host)}"
       end
 
       def message_id_topic_id_regexp
-        @message_id_topic_id_regexp ||= Regexp.new "topic/(\\d+|\\d+\.\\w+)@#{Regexp.escape(host)}"
+        Regexp.new "topic/(\\d+|\\d+\.\\w+)@#{Regexp.escape(host)}"
       end
 
       def message_id_rfc_format(message_id)
@@ -100,7 +100,7 @@ module Email
       end
 
       def host
-        @host ||= Email::Sender.host_for(Discourse.base_url)
+        Email::Sender.host_for(Discourse.base_url)
       end
     end
   end
diff --git a/spec/lib/message_id_service_spec.rb b/spec/lib/message_id_service_spec.rb
index 65077ca5818..3b8a581faac 100644
--- a/spec/lib/message_id_service_spec.rb
+++ b/spec/lib/message_id_service_spec.rb
@@ -120,4 +120,12 @@ describe Email::MessageIdService do
       expect(Email::MessageIdService.message_id_clean(message_id)).to eq(message_id)
     end
   end
+
+  describe "#host" do
+    it "handles hostname changes at runtime" do
+      expect(Email::MessageIdService.host).to eq("test.localhost")
+      SiteSetting.force_hostname = "other.domain.example.com"
+      expect(Email::MessageIdService.host).to eq("other.domain.example.com")
+    end
+  end
 end