Merge branch 'bugfix/html-only-mail' into 'master'

add parsing support for incoming html email

## What does this MR do?
Fixes #18388 by adding support for parsing HTML email

## Are there points in the code the reviewer needs to double check?
The new class, Gitlab::Email::HTMLParser, which needs to translate the HTML content to text and also delete replies, as they are not necessarily in the correct format to be caught by EmailReplyParser. The solution I found that should work for any HTML-formatted email is to remove all `<table>` and `<blockquote>` tags. Actual `<table>` elements (to be interpreted by markdown) should already be encoded with e.g. `&lt;table&gt;` - the only failure mode is if there is an *actual* HTML table in the content itself, which we wouldn't be able to support easily anyways.

The gem `html2text` traverses the HTML tree and outputs text - and markdown in the case of HTML links or images.

See merge request !7397

1 files changed, 4 insertions, 0 deletions

diff --git a/spec/lib/gitlab/email/reply_parser_spec.rb b/spec/lib/gitlab/email/reply_parser_spec.rb
index 6f8e9a4be64..c7a0139d32a 100644
--- a/spec/lib/gitlab/email/reply_parser_spec.rb
+++ b/spec/lib/gitlab/email/reply_parser_spec.rb
@@ -206,5 +206,9 @@ describe Gitlab::Email::ReplyParser, lib: true do
     it "properly renders email reply from MS Outlook client" do
       expect(test_parse_body(fixture_file("emails/outlook.eml"))).to eq("Microsoft Outlook 2010")
     end
+
+    it "properly renders html-only email from MS Outlook" do
+      expect(test_parse_body(fixture_file("emails/outlook_html.eml"))).to eq("Microsoft Outlook 2010")
+    end
   end
 end