Set email content with maintype when needed and correctly set Content-Language header

When the content is not a string, EmailMessage.set_content requires a maintype
argument but not when it is a string. The maintype is then deduced using the
mimetypes module.
The Content-Language of content or alternate must be set using the headers
parameter instead of params which is for the Content-Type.
And finally the Content-Language must be set on the main message only if it
contains multiparts otherwise it is set twice.

Closes #14028

trytond/setup.py

@@ -53,7 +53,7 @@ else:
     download_url = 'http://downloads.tryton.org/%s.%s/' % (
         major_version, minor_version)
 
-tests_require = ['pillow', 'pydot']
+tests_require = ['pillow', 'pydot', 'html2text']
 
 setup(name=name,
     version=version,

trytond/trytond/report/report.py

@@ -4,6 +4,7 @@ import datetime
 import inspect
 import logging
 import math
+import mimetypes
 import operator
 import os
 import pathlib
@@ -594,7 +595,7 @@ def get_email(report, record, languages):
     converter = None
     title = None
     msg = EmailMessage()
-    msg.add_header('Content-Language', ', '.join(l.code for l in languages))
+    header_factory = msg.policy.header_factory
     for alternative, language in enumerate(languages):
         with Transaction().set_context(
                 language=language.code, with_rec_name=False):
@@ -603,21 +604,36 @@ def get_email(report, record, languages):
                     'action_id': report_id,
                     'language': language,
                     })
-        if ext == 'txt':
-            ext = 'plain'
-        if ext == 'html' and html2text:
+        for map in [mimetypes.types_map, mimetypes.common_types]:
+            if '.' + ext in map:
+                mimetype = map['.' + ext]
+                maintype, subtype = mimetype.split('/')
+                break
+        else:
+            maintype, subtype = 'application', ext
+        if maintype == 'text' and subtype == 'html' and html2text:
             if not converter:
                 converter = html2text.HTML2Text()
             content_text = converter.handle(content)
-            msg.add_alternative(content_text, subtype='plain', params={
-                    'Content-Language': language.code,
-                    })
+            msg.add_alternative(content_text, subtype='plain', headers=[
+                    header_factory('Content-Language', language.code),
+                    ])
+        types = {
+            'subtype': subtype,
+            }
+        if not isinstance(content, str):
+            types['maintype'] = maintype
         if alternative or msg.is_multipart():
-            msg.add_alternative(content, subtype=ext, params={
-                    'Content-Language': language.code,
-                    })
+            msg.add_alternative(
+                content, **types, headers=[
+                    header_factory('Content-Language', language.code),
+                    ])
         else:
-            msg.set_content(content, subtype=ext, params={
-                    'Content-Language': language.code,
-                    })
+            msg.set_content(
+                content, **types, headers=[
+                    header_factory('Content-Language', language.code),
+                    ])
+    if msg.is_multipart():
+        msg.add_header(
+            'Content-Language', ', '.join(l.code for l in languages))
     return msg, title

trytond/trytond/tests/test_report.py

@@ -1,12 +1,15 @@
 # This file is part of Tryton.  The COPYRIGHT file at the top level of
 # this repository contains the full copyright notices and license terms.
 import datetime
+from email.message import EmailMessage
+from unittest.mock import Mock, patch
 
 from trytond.model.exceptions import AccessError
 from trytond.pool import Pool
-from trytond.report.report import Report
+from trytond.report.report import Report, get_email
 from trytond.tests.test_tryton import (
     TestCase, activate_module, with_transaction)
+from trytond.transaction import Transaction
 
 
 class ReportTestCase(TestCase):
@@ -84,6 +87,115 @@ class ReportTestCase(TestCase):
         with self.assertRaises(AccessError):
             Report.execute([1], {'model': 'test.access'})
 
+    @with_transaction()
+    def test_get_email_html(self):
+        "Test get email"
+        class FakeReport(Report):
+            @classmethod
+            def execute(cls, *args, **kwargs):
+                return (
+                    'html', '<!doctype html><title>Test</title>', False,
+                    "Title")
+
+        record = Mock()
+        language = Mock()
+        language.code = 'en'
+        msg, title = get_email(FakeReport, record, [language])
+
+        self.assertEqual(title, "Title")
+        self.assertIsInstance(msg, EmailMessage)
+        self.assertEqual(msg['Content-Language'], 'en')
+        self.assertTrue(msg.is_multipart())
+
+        plain = msg.get_body(preferencelist=('plain',))
+        self.assertEqual(plain['Content-Language'], 'en')
+        self.assertEqual(plain.get_content().strip(), "Test")
+
+        html = msg.get_body(preferencelist=('html',))
+        self.assertEqual(html['Content-Language'], 'en')
+        self.assertEqual(
+            html.get_content().strip(),
+            '<!doctype html><title>Test</title>')
+
+    @with_transaction()
+    @patch('trytond.report.report.html2text')
+    def test_get_email_html_without_html2text(self, html2text):
+        html2text.__bool__.side_effect = lambda: False
+
+        class FakeReport(Report):
+            @classmethod
+            def execute(cls, *args, **kwargs):
+                return (
+                    'html', '<!doctype html><title>Test</title>', False,
+                    "Title")
+
+        record = Mock()
+        language = Mock()
+        language.code = 'en'
+        msg, title = get_email(FakeReport, record, [language])
+
+        self.assertEqual(title, "Title")
+        self.assertIsInstance(msg, EmailMessage)
+        self.assertEqual(msg['Content-Language'], 'en')
+        self.assertFalse(msg.is_multipart())
+        self.assertEqual(
+            msg.get_content().strip(),
+            '<!doctype html><title>Test</title>')
+
+    @with_transaction()
+    def test_get_email_html_multilanguage(self):
+        "Test get email multi-language"
+        class FakeReport(Report):
+            @classmethod
+            def execute(cls, *args, **kwargs):
+                language = Transaction().language
+                return (
+                    'html', f'<!doctype html><title>{language}</title>',
+                    False, language.upper())
+
+        record = Mock()
+        french = Mock()
+        french.code = 'fr'
+        english = Mock()
+        english.code = 'en'
+        msg, title = get_email(FakeReport, record, [french, english])
+
+        self.assertEqual(title, "EN")
+        self.assertIsInstance(msg, EmailMessage)
+        self.assertEqual(msg['Content-Language'], 'fr, en')
+        self.assertTrue(msg.is_multipart())
+        self.assertEqual(len(list(msg.walk())), 5)
+
+        plain = msg.get_body(preferencelist=('plain',))
+        self.assertEqual(plain['Content-Language'], 'fr')
+        self.assertEqual(plain.get_content().strip(), "fr")
+
+        html = msg.get_body(preferencelist=('html',))
+        self.assertEqual(html['Content-Language'], 'fr')
+        self.assertEqual(
+            html.get_content().strip(),
+            '<!doctype html><title>fr</title>')
+
+    @with_transaction()
+    def test_get_email_binary(self):
+        "Test get email binary"
+        class FakeReport(Report):
+            @classmethod
+            def execute(cls, *args, **kwargs):
+                return 'pdf', b'PDF', False, "Title"
+
+        record = Mock()
+        language = Mock()
+        language.code = 'en'
+        msg, title = get_email(FakeReport, record, [language])
+
+        self.assertEqual(title, "Title")
+        self.assertIsInstance(msg, EmailMessage)
+        self.assertEqual(msg['Content-Language'], 'en')
+        self.assertFalse(msg.is_multipart())
+        self.assertEqual(msg.get_content_maintype(), 'application')
+        self.assertEqual(msg.get_content_subtype(), 'pdf')
+
 
 def create_test_format_timedelta(i, in_, out):
     @with_transaction()