Improve and finish the fallback to the In-Reply-To and References header for the reply-by-email feature2364-fallback-to-in-reply-to-header

A few things to note:
- The IncomingEmail feature is now enabled even without a
  correctly-formatted sub-address
- Message-ID for new thread mail are kept the same so that subsequent
  notifications to this thread are grouped in the thread by the email
  service that receives the notification
  (i.e. In-Reply-To of the answer == Message-ID of the first thread message)
- To maximize our chance to be able to retrieve the reply key, we look
  for it in the In-Reply-To header and the References header
- The pattern for the fallback reply message id is "reply-[key]@[gitlab_host]"
- Improve docs thanks to Axil

1 files changed, 67 insertions, 10 deletions

diff --git a/spec/mailers/shared/notify.rb b/spec/mailers/shared/notify.rb
index eafc5e5044b..56a6dbf96f9 100644
--- a/spec/mailers/shared/notify.rb
+++ b/spec/mailers/shared/notify.rb
@@ -10,6 +10,13 @@ shared_context 'gitlab email notification' do
     ActionMailer::Base.deliveries.clear
     email = recipient.emails.create(email: "notifications@example.com")
     recipient.update_attribute(:notification_email, email.email)
+    stub_incoming_email_setting(enabled: true, address: "reply+%{key}@#{Gitlab.config.gitlab.host}")
+  end
+end
+
+shared_context 'reply-by-email is enabled with incoming address without %{key}' do
+  before do
+    stub_incoming_email_setting(enabled: true, address: "reply@#{Gitlab.config.gitlab.host}")
   end
 end
 
@@ -46,26 +53,76 @@ shared_examples 'an email with X-GitLab headers containing project details' do
   end
 end
 
-shared_examples 'an email starting a new thread' do |message_id_prefix|
-  include_examples 'an email with X-GitLab headers containing project details'
+shared_examples 'a new thread email with reply-by-email enabled' do
+  let(:regex) { /\A<reply\-(.*)@#{Gitlab.config.gitlab.host}>\Z/ }
+
+  it 'has a Message-ID header' do
+    is_expected.to have_header 'Message-ID', "<#{model.class.model_name.singular_route_key}_#{model.id}@#{Gitlab.config.gitlab.host}>"
+  end
 
-  it 'has a discussion identifier' do
-    is_expected.to have_header 'Message-ID',  /<reply\+(.*)@#{Gitlab.config.gitlab.host}>/
-    is_expected.to have_header 'References',  /<#{message_id_prefix}(.*)@#{Gitlab.config.gitlab.host}>/
+  it 'has a References header' do
+    is_expected.to have_header 'References', regex
   end
 end
 
-shared_examples 'an answer to an existing thread' do |thread_id_prefix|
+shared_examples 'a thread answer email with reply-by-email enabled' do
   include_examples 'an email with X-GitLab headers containing project details'
+  let(:regex) { /\A<#{model.class.model_name.singular_route_key}_#{model.id}@#{Gitlab.config.gitlab.host}> <reply\-(.*)@#{Gitlab.config.gitlab.host}>\Z/ }
+
+  it 'has a Message-ID header' do
+    is_expected.to have_header 'Message-ID', /\A<(.*)@#{Gitlab.config.gitlab.host}>\Z/
+  end
+
+  it 'has a In-Reply-To header' do
+    is_expected.to have_header 'In-Reply-To', "<#{model.class.model_name.singular_route_key}_#{model.id}@#{Gitlab.config.gitlab.host}>"
+  end
+
+  it 'has a References header' do
+    is_expected.to have_header 'References', regex
+  end
 
   it 'has a subject that begins with Re: ' do
     is_expected.to have_subject /^Re: /
   end
+end
+
+shared_examples 'an email starting a new thread with reply-by-email enabled' do
+  include_examples 'an email with X-GitLab headers containing project details'
+  include_examples 'a new thread email with reply-by-email enabled'
+
+  context 'when reply-by-email is enabled with incoming address with %{key}' do
+    it 'has a Reply-To header' do
+      is_expected.to have_header 'Reply-To', /<reply+(.*)@#{Gitlab.config.gitlab.host}>\Z/
+    end
+  end
+
+  context 'when reply-by-email is enabled with incoming address without %{key}' do
+    include_context 'reply-by-email is enabled with incoming address without %{key}'
+    include_examples 'a new thread email with reply-by-email enabled'
+
+    it 'has a Reply-To header' do
+      is_expected.to have_header 'Reply-To', /<reply@#{Gitlab.config.gitlab.host}>\Z/
+    end
+  end
+end
+
+shared_examples 'an answer to an existing thread with reply-by-email enabled' do
+  include_examples 'an email with X-GitLab headers containing project details'
+  include_examples 'a thread answer email with reply-by-email enabled'
+
+  context 'when reply-by-email is enabled with incoming address with %{key}' do
+    it 'has a Reply-To header' do
+      is_expected.to have_header 'Reply-To', /<reply+(.*)@#{Gitlab.config.gitlab.host}>\Z/
+    end
+  end
+
+  context 'when reply-by-email is enabled with incoming address without %{key}' do
+    include_context 'reply-by-email is enabled with incoming address without %{key}'
+    include_examples 'a thread answer email with reply-by-email enabled'
 
-  it 'has headers that reference an existing thread' do
-    is_expected.to have_header 'Message-ID',  /<(.*)@#{Gitlab.config.gitlab.host}>/
-    is_expected.to have_header 'References',  /<#{thread_id_prefix}(.*)@#{Gitlab.config.gitlab.host}>/
-    is_expected.to have_header 'In-Reply-To', /<#{thread_id_prefix}(.*)@#{Gitlab.config.gitlab.host}>/
+    it 'has a Reply-To header' do
+      is_expected.to have_header 'Reply-To', /<reply@#{Gitlab.config.gitlab.host}>\Z/
+    end
   end
 end