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

Gemfile

@@ -330,6 +330,7 @@ gem 'octokit', '~> 4.3.0'
 gem 'mail_room', '~> 0.9.0'
 
 gem 'email_reply_parser', '~> 0.5.8'
+gem 'html2text'
 
 gem 'ruby-prof', '~> 0.16.2'
 

Gemfile.lock

@@ -345,6 +345,8 @@ GEM
     html-pipeline (1.11.0)
       activesupport (>= 2)
       nokogiri (~> 1.4)
+    html2text (0.2.0)
+      nokogiri (~> 1.6)
     htmlentities (4.3.4)
     httparty (0.13.7)
       json (~> 1.8)
@@ -881,6 +883,7 @@ DEPENDENCIES
   health_check (~> 2.2.0)
   hipchat (~> 1.5.0)
   html-pipeline (~> 1.11.0)
+  html2text
   httparty (~> 0.13.3)
   influxdb (~> 0.2)
   jira-ruby (~> 1.1.2)

changelogs/unreleased/bugfix-html-only-mail.yml

+---
+title: Add support for reply-by-email when the email only contains HTML
+merge_request: 7397
+author:

lib/gitlab/email/html_parser.rb

+module Gitlab
+  module Email
+    class HTMLParser
+      def self.parse_reply(raw_body)
+        new(raw_body).filtered_text
+      end
+
+      attr_reader :raw_body
+      def initialize(raw_body)
+        @raw_body = raw_body
+      end
+
+      def document
+        @document ||= Nokogiri::HTML.parse(raw_body)
+      end
+
+      def filter_replies!
+        document.xpath('//blockquote').each(&:remove)
+        document.xpath('//table').each(&:remove)
+      end
+
+      def filtered_html
+        @filtered_html ||= begin
+          filter_replies!
+          document.inner_html
+        end
+      end
+
+      def filtered_text
+        @filtered_text ||= Html2Text.convert(filtered_html)
+      end
+    end
+  end
+end

lib/gitlab/email/reply_parser.rb

@@ -23,19 +23,26 @@ module Gitlab
       private
 
       def select_body(message)
-        text    = message.text_part if message.multipart?
-        text  ||= message           if message.content_type !~ /text\/html/
+        if message.multipart?
+          part = message.text_part || message.html_part || message
+        else
+          part = message
+        end
 
-        return "" unless text
+        decoded = fix_charset(part)
 
-        text = fix_charset(text)
+        return "" unless decoded
 
         # Certain trigger phrases that means we didn't parse correctly
-        if text =~ /(Content\-Type\:|multipart\/alternative|text\/plain)/
+        if decoded =~ /(Content\-Type\:|multipart\/alternative|text\/plain)/
           return ""
         end
 
-        text
+        if (part.content_type || '').include? 'text/html'
+          HTMLParser.parse_reply(decoded)
+        else
+          decoded
+        end
       end
 
       # Force encoding to UTF-8 on a Mail::Message or Mail::Part

spec/fixtures/emails/outlook_html.eml

+
+MIME-Version: 1.0
+Received: by 10.25.161.144 with HTTP; Tue, 7 Oct 2014 22:17:17 -0700 (PDT)
+X-Originating-IP: [117.207.85.84]
+In-Reply-To: <5434c8b52bb3a_623ff09fec70f049749@discourse-app.mail>
+References: <topic/35@discourse.techapj.com>
+  <5434c8b52bb3a_623ff09fec70f049749@discourse-app.mail>
+Date: Wed, 8 Oct 2014 10:47:17 +0530
+Delivered-To: arpit@techapj.com
+Message-ID: <CAOJeqne=SJ_LwN4sb-0Y95ejc2OpreVhdmcPn0TnmwSvTCYzzQ@mail.gmail.com>
+Subject: Re: [Discourse] [Meta] Welcome to techAPJ's Discourse!
+From: Arpit Jalan <arpit@techapj.com>
+To: Discourse <mail+e1c7f2a380e33840aeb654f075490bad@arpitjalan.com>Accept-Language: en-US
+Content-Language: en-US
+X-MS-Has-Attach:
+X-MS-TNEF-Correlator:
+x-originating-ip: [134.68.31.227]
+Content-Type: multipart/alternative;
+        boundary="_000_B0DFE1BEB3739743BC9B639D0E6BC8FF217A6341IUMSSGMBX104ads_"
+MIME-Version: 1.0
+
+--_000_B0DFE1BEB3739743BC9B639D0E6BC8FF217A6341IUMSSGMBX104ads_
+Content-Type: text/html; charset="utf-8"
+Content-Transfer-Encoding: base64
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+--_000_B0DFE1BEB3739743BC9B639D0E6BC8FF217A6341IUMSSGMBX104ads_--

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