add get_encoding() and encode_text()

app/email_utils.py

@@ -1,5 +1,7 @@
+import base64
 import email
 import os
+import quopri
 import random
 import re
 from email.header import decode_header
@@ -671,6 +673,33 @@ def is_valid_email(email_address: str) -> bool:
     )
 
 
+def get_encoding(msg: Message) -> str:
+    """
+    Return the message encoding, possible values:
+    - quoted-printable
+    - base64: default if unknown
+    """
+    cte = str(msg.get("content-transfer-encoding", "")).lower()
+    if cte == "":
+        return "base64"
+
+    if cte == "quoted-printable" or cte == "base64":
+        return cte
+
+    LOG.exception("Unknown encoding %s", cte)
+
+    return "base64"
+
+
+def encode_text(text: str, encoding: str = "base64") -> str:
+    if encoding == "quoted-printable":
+        encoded = quopri.encodestring(text.encode("utf-8"))
+        return str(encoded, "utf-8")
+    else:  # use base64 by default
+        encoded = base64.b64encode(text.encode("utf-8"))
+        return str(encoded, "utf-8")
+
+
 def add_header(msg: Message, text_header, html_header) -> Message:
     if msg.get_content_type() == "text/plain":
         payload = msg.get_payload()

tests/test_email_utils.py

@@ -18,6 +18,8 @@ from app.email_utils import (
     to_bytes,
     generate_reply_email,
     normalize_reply_email,
+    get_encoding,
+    encode_text,
 )
 from app.extensions import db
 from app.models import User, CustomDomain
@@ -416,3 +418,23 @@ def test_generate_reply_email(flask_client):
 def test_normalize_reply_email(flask_client):
     assert normalize_reply_email("re+abcd@sl.local") == "re+abcd@sl.local"
     assert normalize_reply_email('re+"ab cd"@sl.local') == "re+_ab_cd_@sl.local"
+
+
+def test_get_encoding():
+    msg = email.message_from_string("")
+    assert get_encoding(msg) == "base64"
+
+    msg = email.message_from_string("Content-TRANSFER-encoding: Invalid")
+    assert get_encoding(msg) == "base64"
+
+    msg = email.message_from_string("Content-TRANSFER-encoding: quoted-printable")
+    assert get_encoding(msg) == "quoted-printable"
+
+
+def test_encode_text():
+    assert encode_text("") == ""
+    assert encode_text("ascii") == "YXNjaWk="
+    assert encode_text("ascii", "quoted-printable") == "ascii"
+
+    assert encode_text("mèo méo") == "bcOobyBtw6lv"
+    assert encode_text("mèo méo", "quoted-printable") == "m=C3=A8o m=C3=A9o"