Close #334 - test mails with broken header encoding

The mail gem below 2.7.0 is not able to handle emails with broken
charset encoding in headers.

This is an issue that must be fixed in the mail gem, but we are
adding a test to document this and be sure to not have regressions
with future versions of mail.

CHANGELOG.md

@@ -12,6 +12,9 @@ This project adheres to [Semantic Versioning](http://semver.org/).
 * Do not anymore fail on emails containing any PGP boundaries as part of their plain text. As a sideeffect we will not anymore validate an email a second time. Hence, a message part containing an additional signature within an encrypted (and possibly signed) email won't be validated and removed. (#261)
 * Exit with code 1 if a CLI-subcommand was not found (#339).
 
+### Known issues
+
+* With the current used mail library version schleuder uses, there are certain malformed emails that can't be parsed. See #334 for background. This will be fixed in future releases of the mail library.
 
 ### Changed
 

spec/fixtures/mails/broken_utf8_charset.eml

+Return-Path: <le.savoirmagnetisme@gmail.com>
+Delivered-To: example@example.org
+Received: from mail.example.org (mail.example.org [192.168.1.2])
+	(using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits))
+	(No client certificate requested)
+	by trebuchet.example.org (Postfix) with ESMTPS id 2C8A1A0403
+	for <example@example.org>; Sat, 10 Mar 2018 02:52:58 +0100 (CET)
+Received: from [127.0.0.1] (localhost [127.0.0.1])example.org (mx.example.org [192.168.1.1])
+	(using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits))
+	(No client certificate requested)
+	by mail.example.org (Postfix) with ESMTPS id 7FB4610F
+	for <example@example.org>; Sat, 10 Mar 2018 02:52:57 +0100 (CET)
+Received: from [127.0.0.1] (localhost [127.0.0.1])ng TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits))
+	(No client certificate requested)
+	by mx2.example.org (Postfix) with ESMTPS id DA6D2880A0
+	for <example@example.org>; Sat, 10 Mar 2018 02:52:54 +0100 (CET)
+Received: from [127.0.0.1] (localhost [127.0.0.1])novol420-pc (unknown [192.168.1.3])
+	by smtp1-g21.free.fr (Postfix) with SMTP id 95E05B0051B
+	for <example@example.org>; Sat, 10 Mar 2018 02:52:51 +0100 (CET)
+Message-ID: <afccb596bc81341399153df738c8788c@gmail.com>
+From: "Invitation" <le.savoirmagnetisme@gmail.com>
+To: <example@example.org>
+Subject: =?windows-1258?B?c29pcull?=
+Date: Sat, 10 Mar 2018 02:52:36 +0100
+MIME-Version: 1.0
+Content-Type: multipart/alternative;
+	boundary="----=MailPart0000_0010_0A37C499"
+
+This is a multi-part message in MIME format.
+
+------=MailPart0000_0010_0A37C499
+Content-Type: text/plain;
+	charset="windows-1258"
+Content-Transfer-Encoding: quoted-printable
+
+
+
+
+=20
+
+
+
+
+
+=20
+
+
+
+------=MailPart0000_0010_0A37C499--
+

spec/schleuder/runner_spec.rb

@@ -395,6 +395,28 @@ describe Schleuder::Runner do
 
       teardown_list_and_mailer(list)
     end
+
+    it 'does not throw an error on emails with broken utf-8' do
+      list = create(:list, send_encrypted_only: false)
+      list.subscribe("admin@example.org", nil, true)
+      mail = File.read('spec/fixtures/mails/broken_utf8_charset.eml')
+
+      # From mail 2.7.0 this is handled correctly
+      # See #334 for background
+      if Gem::Version.new(Mail::VERSION.version) < Gem::Version.new('2.7.0')
+        expect{
+          Schleuder::Runner.new().run(mail, list.email)
+        }.to raise_error(ArgumentError)
+      else
+        Schleuder::Runner.new().run(mail, list.email)
+        message = Mail::TestMailer.deliveries.first
+
+        output = process_mail(message.to_s, list.email)
+        expect(output).to be nil
+      end
+
+      teardown_list_and_mailer(list)
+    end
   end
   context 'after keyword parsing' do
     it 'falls back to default charset per RFC if none is set' do